Troubleshooting - IP Service

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Troubleshooting - IP Service
Quidway S9300 Terabit Routing Switch
V100R003C00
Troubleshooting - IP Service
Issue
01
Date
2010-07-15
HUAWEI TECHNOLOGIES CO., LTD.
Copyright © Huawei Technologies Co., Ltd. 2010. All rights reserved.
No part of this document may be reproduced or transmitted in any form or by any means without prior written
consent of Huawei Technologies Co., Ltd.
Trademarks and Permissions
and other Huawei trademarks are trademarks of Huawei Technologies Co., Ltd.
All other trademarks and trade names mentioned in this document are the property of their respective holders.
Notice
The purchased products, services and features are stipulated by the contract made between Huawei and the
customer. All or part of the products, services and features described in this document may not be within the
purchase scope or the usage scope. Unless otherwise specified in the contract, all statements, information,
and recommendations in this document are provided "AS IS" without warranties, guarantees or representations
of any kind, either express or implied.
The information in this document is subject to change without notice. Every effort has been made in the
preparation of this document to ensure accuracy of the contents, but all statements, information, and
recommendations in this document do not constitute the warranty of any kind, express or implied.
Huawei Technologies Co., Ltd.
Address:
Huawei Industrial Base
Bantian, Longgang
Shenzhen 518129
People's Republic of China
Website:
http://www.huawei.com
Email:
[email protected]
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About This Document
About This Document
Intended Audience
This document describes the process of troubleshooting the IP address, and UDP Helper, and
provides typical troubleshooting cases.
This document is intended for:
l
Network planning engineers
l
Hardware installation engineers
l
Commissioning engineers
l
Data configuration engineers
Symbol Conventions
The symbols that may be found in this document are defined as follows.
Symbol
Description
DANGER
WARNING
CAUTION
Issue 01 (2010-07-15)
Indicates a hazard with a high level of risk, which if not
avoided, will result in death or serious injury.
Indicates a hazard with a medium or low level of risk, which
if not avoided, could result in minor or moderate injury.
Indicates a potentially hazardous situation, which if not
avoided, could result in equipment damage, data loss,
performance degradation, or unexpected results.
TIP
Indicates a tip that may help you solve a problem or save
time.
NOTE
Provides additional information to emphasize or supplement
important points of the main text.
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About This Document
Command Conventions
The command conventions that may be found in this document are defined as follows.
Convention
Description
Boldface
The keywords of a command line are in boldface.
Italic
Command arguments are in italics.
[]
Items (keywords or arguments) in brackets [ ] are optional.
{ x | y | ... }
Optional items are grouped in braces and separated by
vertical bars. One item is selected.
[ x | y | ... ]
Optional items are grouped in brackets and separated by
vertical bars. One item is selected or no item is selected.
{ x | y | ... }*
Optional items are grouped in braces and separated by
vertical bars. A minimum of one item or a maximum of all
items can be selected.
[ x | y | ... ]*
Optional items are grouped in brackets and separated by
vertical bars. Several items or no item can be selected.
&<1-n>
The parameter before the & sign can be repeated 1 to n times.
#
A line starting with the # sign is comments.
Change History
Changes between document issues are cumulative. Therefore, the latest document issue contains
all changes made in previous issues.
Changes in Issue 01 (2010-07-15)
Initial commercial release.
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Contents
Contents
About This Document...................................................................................................................iii
1 IP Addressing Troubleshooting..............................................................................................1-1
1.1 IP Addressing Overview.................................................................................................................................1-2
1.1.1 Classification of IP Addresses................................................................................................................1-2
1.1.2 IP Address Unnumbered........................................................................................................................1-5
1.1.3 References..............................................................................................................................................1-5
1.2 Configuring the IP Address of an Interface Troubleshooting.........................................................................1-5
1.2.1 Typical Networking................................................................................................................................1-5
1.2.2 Configuration Notes...............................................................................................................................1-6
1.2.3 Troubleshooting Flowchart....................................................................................................................1-6
1.2.4 Troubleshooting Procedure....................................................................................................................1-7
1.3 Configuring the IP Address Unnumbered of an Interface Troubleshooting...................................................1-8
1.3.1 Typical Networking................................................................................................................................1-8
1.3.2 Configuration Notes...............................................................................................................................1-8
1.3.3 Troubleshooting Flowchart....................................................................................................................1-9
1.3.4 Troubleshooting Procedure....................................................................................................................1-9
1.4 Troubleshooting Cases..................................................................................................................................1-10
1.4.1 Can not Borrow an IP Address.............................................................................................................1-11
2 DHCP Troubleshooting............................................................................................................2-1
2.1 Introduction to DHCP.....................................................................................................................................2-2
2.1.1 DHCP Server..........................................................................................................................................2-2
2.1.2 DHCP Relay...........................................................................................................................................2-3
2.1.3 DHCP Proxy...........................................................................................................................................2-3
2.1.4 Procedure for Obtaining the IP Address from the DHCP Server or the DHCP Relay Agent................2-4
2.1.5 DHCP Proxy Procedure.........................................................................................................................2-6
2.2 Troubleshooting of the DHCP Server Based on the Global Address Pool.....................................................2-7
2.2.1 Typical Networking................................................................................................................................2-7
2.2.2 Configuration Notes...............................................................................................................................2-8
2.2.3 Troubleshooting Flowchart....................................................................................................................2-9
2.2.4 Troubleshooting Procedure..................................................................................................................2-11
2.3 DHCP Relay Troubleshooting......................................................................................................................2-12
2.3.1 Typical Networking..............................................................................................................................2-12
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2.3.2 Configuration Notes.............................................................................................................................2-13
2.3.3 Troubleshooting Flowchart..................................................................................................................2-13
2.3.4 Troubleshooting Procedure..................................................................................................................2-14
2.4 Troubleshooting Cases..................................................................................................................................2-15
2.4.1 IP Address Assigned by the DHCP Server to a DHCP Client Conflicts with That of Another DHCP Client
.......................................................................................................................................................................2-15
2.4.2 DHCP Client Cannot Obtain an IP Address from the DHCP Server...................................................2-17
2.4.3 DHCP Client Cannot Obtain an IP Address Through the DHCP Relay Agent...................................2-18
3 DHCPv6 Troubleshooting........................................................................................................3-1
3.1 DHCPv6 Relay Troubleshooting.................................................................................................................... 3-2
3.1.1 Troubleshooting Flowchart....................................................................................................................3-2
3.1.2 Troubleshooting Procedure....................................................................................................................3-4
3.2 Troubleshooting Cases....................................................................................................................................3-5
3.2.1 Clients Cannot Obtain IPv6 Addresses Through DHCPv6 Relay......................................................... 3-5
4 UDP Helper Troubleshooting..................................................................................................4-1
4.1 UDP Helper Overview....................................................................................................................................4-2
4.2 UDP Helper Troubleshooting..........................................................................................................................4-2
4.2.1 Typical Networking................................................................................................................................4-2
4.2.2 Configuration Notes...............................................................................................................................4-3
4.2.3 Troubleshooting Flowchart....................................................................................................................4-4
4.2.4 Troubleshooting Procedure....................................................................................................................4-5
4.3 Troubleshooting Cases....................................................................................................................................4-6
4.3.1 UDP Packets Cannot Be Relayed to the Destination Server..................................................................4-6
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Figures
Figures
Figure 1-1 Five IP address classes.......................................................................................................................1-2
Figure 1-2 Typical Networking diagram of IP address configuration on an interface.........................................1-6
Figure 1-3 Troubleshooting flowchart of IP addressing......................................................................................1-6
Figure 1-4 Typical networking diagram of IP address unnumbered configuration on an interface.....................1-8
Figure 1-5 Troubleshooting flowchart of IP address unnumbered.......................................................................1-9
Figure 1-6 Networking diagram of IP address unnumbered..............................................................................1-11
Figure 2-1 Typical networking diagram of the DHCP server..............................................................................2-2
Figure 2-2 Typical networking diagram of the DHCP relay agent......................................................................2-3
Figure 2-3 Typical networking diagram of DHCP proxy....................................................................................2-4
Figure 2-4 Procedure for obtaining the IP address from the DHCP server or the DHCP relay agent.................2-5
Figure 2-5 DHCP proxy procedure......................................................................................................................2-6
Figure 2-6 Typical networking of the DHCP server............................................................................................2-8
Figure 2-7 Troubleshooting flowchart of the DHCP server based on the global address pool..........................2-10
Figure 2-8 Typical networking of DHCP relay..................................................................................................2-12
Figure 2-9 Troubleshooting flowchart of DHCP relay......................................................................................2-14
Figure 2-10 Conflict of the IP addresses obtained from the DHCP server........................................................2-16
Figure 2-11 Networking where a DHCP client cannot obtain an IP address from the DHCP server................2-17
Figure 2-12 Networking where a DHCP client cannot obtain an IP address through the DHCP relay agent
.............................................................................................................................................................................2-18
Figure 3-1 DHCPv6 relay troubleshooting flowchart..........................................................................................3-3
Figure 3-2 Networking where clients cannot obtain IPv6 addresses...................................................................3-6
Figure 4-1 Typical networking diagram of the UDP helper.................................................................................4-2
Figure 4-2 UDP helper troubleshooting flowchart...............................................................................................4-5
Figure 4-3 Networking diagram of the UDP helper.............................................................................................4-7
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Tables
Tables
Table 1-1 Classification and range of IP addresses..............................................................................................1-3
Table 1-2 Some special IP addresses....................................................................................................................1-4
Table 1-3 Private IP addresses..............................................................................................................................1-5
Table 1-4 Error prompts and the corresponding ways to rectify the faults..........................................................1-7
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1
1 IP Addressing Troubleshooting
IP Addressing Troubleshooting
About This Chapter
Describes the knowledge related to IP address troubleshooting, including IP address overview,
troubleshooting flowchart and troubleshooting procedure in a typical networking,
troubleshooting cases.
1.1 IP Addressing Overview
Describes the knowledge you need to know before troubleshooting the IP addressing.
1.2 Configuring the IP Address of an Interface Troubleshooting
Describes the notes about IP addressing, and provides the relevant troubleshooting flowchart
and the troubleshooting procedure in a typical networking for IP addressing.
1.3 Configuring the IP Address Unnumbered of an Interface Troubleshooting
Describes the notes about IP address unnumbered, provides the relevant troubleshooting
flowchart and the troubleshooting procedure in a typical networking for IP address unnumbered.
1.4 Troubleshooting Cases
This section presents several troubleshooting cases.
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1.1 IP Addressing Overview
Describes the knowledge you need to know before troubleshooting the IP addressing.
1.1.1 Classification of IP Addresses
1.1.2 IP Address Unnumbered
1.1.3 References
1.1.1 Classification of IP Addresses
To communicate with each other in an IP network, each host on the network must be assigned
an IP address. If you want to connect a computer to the Internet, you need to apply an IP address
from the Internet Service Provider (ISP). An IP address has 32 bits, composed of the following
two parts:
l
Network ID field (net-ID): It is applied to distinguish networks. The first bits of the net-ID
are called the class field (or class bits). These bits are used to distinguish the IP address
classes.
l
Host ID field (host-ID): It is applied to distinguish different hosts on the network.
Five IP Address Classes
As shown in Figure 1-1, IP addresses are further classified into five classes to facilitate IP
address management and networking. You can judge the class of an IP address through the first
bits in the network ID field.
Figure 1-1 Five IP address classes
0
15
7
A
0
B
1 0
C
1 1 0
D
1 1 1 0
Multicast-address
E
1 1 1 1
Reserved
Net-id
31
23
Host-id
Net-id
Host-id
Net-id
Host-id
At present, the commonly adopted IP addresses are Class A, Class B, and Class C addresses.
Class D addresses are multicast addresses. Addresses in Class E are reserved. For detailed
description of IP address classification. Refer to RFC 1166.
Some IP addresses are reserved for particular purposes, and they cannot be applied by common
users. Table 1-1 lists the ranges of IP addresses for all five classes.
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Table 1-1 Classification and range of IP addresses
Class
Address
Range
Available IP
Network Range
Description
A
0.0.0.0 to
127.255.255.25
5
1.0.0.0 to
126.0.0.0
The IP addresses with host IDs as all 0s are
network addresses, and are used for
network routing.
The IP addresses with host IDs as all 1s are
broadcast addresses, that is, the broadcast
to all hosts on the network.
The IP address 0.0.0.0 is used only for
temporary communication during system
start-up in the Dynamic Host
Configuration Protocol (DHCP) mode. It
cannot be an effective destination address.
The IP address with network IDs as 0s
represents the current network, which
indicates that the device can use the current
network even if it does not know the
network ID of the network.
The IP addresses with the network ID in
the format of 127.X.Y.Z are reserved for
the loopback test. The packets sent to these
addresses will not be outputted to the
network. The packets are processed
internally and considered as input packets.
B
128.0.0.0 to
191.255.255.25
5
128.1.0.0 to
191.254.0.0
The IP addresses with host IDs as all 0s are
network addresses, and are used for
network routing.
The IP addresses with host IDs as all 1s are
broadcast addresses, that is, the broadcast
to all hosts on the network.
C
192.0.0.0 to
223.255.255.25
5
192.0.1.0 to
223.255.254.0
The IP addresses with host IDs as all 0s are
network addresses, and are used for
network routing.
The IP addresses with host IDs as all 1s are
broadcast addresses, that is, the broadcast
to all hosts on the network.
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D
224.0.0.0 to
239.255.255.25
5
None
The addresses in Class D are multicast
addresses.
E
240.0.0.0 to
255.255.255.25
5
None
The addresses are reserved for future use.
The IP address 255.255.255.255 is used as
the LAN broadcast address.
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Special IP Addresses
In actual applications, some special IP addresses exist. See Table 1-2 to find their ranges and
description.
Table 1-2 Some special IP addresses
Networ
k ID
Subnet
ID
Host ID
Source
Address
Destination
Address
Description
All 0s
-
All 0s
OK
Never
This kind of addresses is
applied to the hosts on the
network.
All 0s
-
Host ID
OK
Never
This kind of addresses is
applied to the specified
hosts on the network.
127
-
Any value
OK
OK
This kind of addresses is
applied to the loopback
addresses.
All 1s
-
All 1s.
Never
OK
This kind of addresses is
applied to the limited
broadcasts (never
forwarded).
net-id
-
All 1s
Never
OK
This kind of addresses is
applied to send broadcast
packets to the network
specified by the net-id.
net-id
subnetid
All 1s
Never
OK
This kind of addresses is
applied to send broadcast
packets to the subnets
specified by the net-id
and subnet-id.
net-id
All 1s
All 1s
Never
OK
This kind of addresses is
applied to send broadcast
packets to all subnets
specified by the net-id.
NOTE
net-id and subnet-id indicate that the corresponding fields that are neither all 0s nor all 1s.
Private IP Addresses
To solve the problem of IP address shortage, the concept of private IP address is introduced.
Private addresses indicate the IP addresses of internal networks or hosts. These IP addresses can
only be used in the internal network, rather than the public network. Three IP address segments
reserved for the private network are described in RFC 1918. The organization responsible for
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IP address allocation reserves the following IP addresses as the private network addresses. See
Table 1-3 for details:
Table 1-3 Private IP addresses
Network Classification
Address Range
A
10.0.0.0 to 10.255.255.255
B
172.16.0.0 to 172.31.255.255
C
192.168.0.0 to 192.168.255.255
1.1.2 IP Address Unnumbered
IP Address Unnumbered can be applied in the following scenario: An interface has no IP address;
then it can utilize the IP address of another interface. The main purpose of IP address unnumbered
is to save IP address resources.
An interface without an IP address cannot generate routes and forward packets. IP address
unnumbered, in essence, is to utilize an interface without the IP address being configured, by
"borrowing" an IP address from another interface.
1.1.3 References
For more information on IP addresses, refer to the following documents:
l
RFC 1166: Internet Numbers
l
RFC 1918: Address Allocation for Private Internets
1.2 Configuring the IP Address of an Interface
Troubleshooting
Describes the notes about IP addressing, and provides the relevant troubleshooting flowchart
and the troubleshooting procedure in a typical networking for IP addressing.
1.2.1 Typical Networking
1.2.2 Configuration Notes
1.2.3 Troubleshooting Flowchart
1.2.4 Troubleshooting Procedure
1.2.1 Typical Networking
Figure 1-2 shows the typical networking diagram of IP address configuration on an interface.
Troubleshooting IP addressing is based on this diagram.
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Figure 1-2 Typical Networking diagram of IP address configuration on an interface
GE1/0/0
VLANIF10
10.1.1.1
GE1/0/0
VLANIF10
10.1.1.2
Internet
SwitchB
SwitchA
1.2.2 Configuration Notes
Item
Notes
Configuring an IP
address
To configure the IP address for an interface, you need to configure the
IP address and the subnet mask at the same time.
To configure an IP address, run the ip address ip-address mask
command in the interface view.
1.2.3 Troubleshooting Flowchart
As to the networking diagram shown in 1.2.1 Typical Networking, if the following error
prompts are displayed, perform based on the flowchart in Figure 1-3:
Figure 1-3 Troubleshooting flowchart of IP addressing
IP addressing
on an
interface fails
A prompt is
displayed?
No
Seek technical
support
Yes
Find a solution
according to the
displayed prompt
Is fault
rectified?
No
Yes
End
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1.2.4 Troubleshooting Procedure
Procedure
Step 1 Check the error prompts and find the corresponding ways to rectify the faults.
Table 1-4 Error prompts and the corresponding ways to rectify the faults
Error Prompt
Description
Error: The specified IP address is
invalid.
The prompt indicates that the IP address is invalid.
The IP address or the subnet mask may be wrongly
configured. Then reconfigure the IP address.
Error: The specified address conflicts
with another address.
The prompt indicates that IP addresses conflict. The
IP address conflict is caused by the repetitious use of
the IP address by another interface in the device.
Please configure a different IP address.
Error: The specified primary address
does not exist.
The prompt indicates that the specific primary IP
address to be deleted does not exist.
Error: Please configure the primary
address in the interface view first.
The prompt indicates that the secondary IP address
cannot be configured. Once IP address unnumbered
is configured, the secondary IP address cannot be
configured.
Error: The number of addresses of the
specified interface reached the upper
limit (32).
The prompt indicates that the number of secondary
IP addresses on an interface exceeds the maximum,
and no more secondary IP address can be configured.
Error: Please delete the sub address in
the interface view first.
The prompt indicates that the primary IP address
cannot be deleted. Before the deletion of a primary IP
address, delete all secondary IP addresses on the
interface.
Error: The specified address cannot
be deleted because it is not the
primary address of this interface.
The prompt indicates that the secondary IP address
cannot be deleted.
Error: The specified sub address does
not exist.
The prompt indicates that the specific secondary IP
address to be deleted does not exist.
Error: The address already exists.
A repetitious secondary IP address is on the interface.
Configure a different secondary IP address.
The secondary IP address cannot be deleted through
the command of the primary IP address deletion. Run
the command of the secondary IP address deletion.
Step 2 No above prompt appears, but you fail to configure the IP address on the interface successfully.
Then contact Huawei technical personnel.
----End
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1.3 Configuring the IP Address Unnumbered of an Interface
Troubleshooting
Describes the notes about IP address unnumbered, provides the relevant troubleshooting
flowchart and the troubleshooting procedure in a typical networking for IP address unnumbered.
1.3.1 Typical Networking
1.3.2 Configuration Notes
1.3.3 Troubleshooting Flowchart
1.3.4 Troubleshooting Procedure
1.3.1 Typical Networking
Figure 1-4 shows the typical networking diagram of IP address unnumbered. Troubleshooting
IP address unnumbered is based on this diagram.
Figure 1-4 Typical networking diagram of IP address unnumbered configuration on an interface
SwitchB
SwitchA
Tunnel
PC1
SwitchC
PC2
1.3.2 Configuration Notes
Item
Notes
Configuring IP
address unnumbered
The Ethernet interface cannot borrow the IP address from another
interface.
The interface with a borrowed IP address has no IP address. So, no
route can be configured for it. The devices should be configured
manually to achieve the interconnection between devices.
To configure IP address unnumbered, run the ip address
unnumbered interface interface-type interface-number command
in the interface view.
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1.3.3 Troubleshooting Flowchart
As to the networking diagram shown in 1.3.1 Typical Networking, if you find any fault in IP
address unnumbered configuration, perform based on the flowchart in Figure 1-5.
Figure 1-5 Troubleshooting flowchart of IP address unnumbered
Fail to borrow an
IP address
Is IP address
unnumbered
configured?
No
Configure IP address
unnumbered on the
interface
Is the fault
rectified?
Yes
No
Yes
Specified
interface has an
IP address?
No
Assign an IP address to
the specified interface
Is the fault
rectified
Yes
No
Yes
Seek technical
support
End
1.3.4 Troubleshooting Procedure
Procedure
Step 1 Check whether IP address unnumbered is configured on the interface.
In the interface view, run the display this command to check whether IP address unnumbered
is configured on the interface. The following is an example:
[S9300A-Tunnel9/0/1] display this
#
interface Tunnel9/0/1
ip address unnumbered interface LoopBack0
#
If IP address unnumbered is not configured, enable the function on the interface.
Step 2 Check whether the interface that needs to lend the IP address has an IP address.
In the interface view, run the display ip interface command to check whether an IP address is
configured on the interface. The following is an example:
[S9300A-Tunnel9/0/1] display ip interface LoopBack 0
LoopBack0 current state : UP
Line protocol current state :UP (spoofing)
The Maximum Transmit Unit : 1500 bytes
input packets : 0, bytes : 0, multicasts : 0
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output packets : 0, bytes : 0, multicasts : 0
Internet Address is 1.1.1.1/32
Broadcast address : 1.1.1.1
TTL invalid packet number:
0
ICMP packet input number:
0
Echo reply:
0
Unreachable:
0
Source quench:
0
Routing redirect:
0
Echo request:
0
Router advert:
0
Router solicit:
0
Time exceed:
0
IP header bad:
0
Timestamp request:
0
Timestamp reply:
0
Information request:
0
Information reply:
0
Netmask request:
0
Netmask reply:
0
Unknown type:
0
If no IP address is configured, configure an IP address on the interface.
Step 3 Check whether information about IP address unnumbered on the interface is correct.
In the interface view, run the display_this_interface command to check whether the interface
can be configured with the IP address unnumbered. The following is an example:
[S9300A-Tunnel9/0/1] display this interface
Tunnel9/0/1 current state : UP
Line protocol current state : DOWN
Description:HUAWEI, Quidway Series, Tunnel9/0/1 Interface
Route Port,The Maximum Transmit Unit is 1500
Internet Address is unnumbered, using address of LoopBack0(1.1.1.1/32)
Encapsulation is TUNNEL, loopback not set
Tunnel protocol is NONE
300 seconds input rate 0 bits/sec, 0 packets/sec
300 seconds output rate 0 bits/sec, 0 packets/sec
0 seconds input rate 0 bits/sec, 0 packets/sec
0 seconds output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes
0 input error
0 packets output, 0 bytes
0 output error
Input:
Unicast: 0 packets, Multicast: 0 packets
Output:
Unicast: 0 packets, Multicast: 0 packets
Input bandwidth utilization : -Output bandwidth utilization : --
If the fault persists, contact Huawei technical personnel.
----End
1.4 Troubleshooting Cases
This section presents several troubleshooting cases.
1.4.1 Can not Borrow an IP Address
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1.4.1 Can not Borrow an IP Address
Fault Symptom
The IP address of the Tunnel interface is ready to be obtained through IP address unnumbered.
The following shows the networking diagram.
Figure 1-6 Networking diagram of IP address unnumbered
SwitchB
SwitchA
Tunnel
PC1
SwitchC
PC2
After the configuration, you find that Tunnel 9/0/1 cannot borrow the IP address of LoopBack0.
Fault Analysis
Check whether Tunnel 9/0/1 is configured with IP address unnumbered. Run the display this
command in the interface view, and you can see the following information:
[S9300-A-Tunnel9/0/1] display this
#
interface Tunnel9/0/1
tunnel-protocol mpls te
mpls te record-route label
mpls te route-pinning
mpls te lsp-tp outbound
#
As shown in the above information, Tunnel 9/0/1 in S9300-A is not configured with the IP
address unnumbered.
Procedure
Step 1 Run the system-view command to enter the system view.
Step 2 Run the interface tunnel 9/0/1 command to enter the Tunnel interface view.
Step 3 Run the ip address unnumbered interface LoopBack 0 command to configure the IP address
unnumbered.
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After the above configuration, you find that Tunnel 9/0/1 on Switch A can borrow the IP address
from LoopBack 0.
----End
Summary
To configure IP address unnumbered, you need:
1-12
l
Firstly ensure that the interface has configured with the IP address unnumbered.
l
Secondly ensure that the lending interface is correctly configured with an IP address.
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2
DHCP Troubleshooting
About This Chapter
This chapter describes troubleshooting of DHCP, including the principle of DHCP, typical
networking, troubleshooting procedure, troubleshooting cases.
2.1 Introduction to DHCP
This section describes the information that you need to know before troubleshooting DHCP.
2.2 Troubleshooting of the DHCP Server Based on the Global Address Pool
This section describes the notes about configuring the DHCP server, and provides the DHCP
snooping troubleshooting flowchart and the troubleshooting procedure in a typical networking
of the DHCP server based on the global address pool.
2.3 DHCP Relay Troubleshooting
This section describes the notes about configuring DHCP relay, and provides the DHCP relay
troubleshooting flowchart and the troubleshooting procedure in a typical DHCP relay
networking.
2.4 Troubleshooting Cases
This section presents the troubleshooting cases.
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2.1 Introduction to DHCP
This section describes the information that you need to know before troubleshooting DHCP.
With the rapid growth in network scales and complexity, for example, the location of hosts
frequently changes (for portable computers or wireless networks) and the number of hosts
exceeds the number of assignable IP addresses, network configurations become more difficult.
The Dynamic Host Configuration Protocol (DHCP) is developed to solve the preceding
problems.
DHCP works in client/server model. The DHCP client requests the DHCP server for the
configuration dynamically, and the DHCP server sends the configuration to the client
dynamically.
2.1.1 DHCP Server
2.1.2 DHCP Relay
2.1.3 DHCP Proxy
2.1.4 Procedure for Obtaining the IP Address from the DHCP Server or the DHCP Relay Agent
2.1.5 DHCP Proxy Procedure
2.1.1 DHCP Server
The S9300 can function as the DHCP server to assign IP addresses to users. Generally, the DHCP
server is used to assign IP addresses in the following scenarios:
l
On a large-scale network, it takes more time to manually assign IP addresses and it is
difficult to manage the entire network
l
The number of hosts on the network is greater than that of the available IP addresses. Thus,
not every host can be assigned a fixed IP address. A large number of clients need to
dynamically obtain IP addresses through the DHCP server. In addition, the number of
concurrent clients is limited.
Figure 2-1 shows a typical networking diagram of the DHCP server.
Figure 2-1 Typical networking diagram of the DHCP server
Switch
GE 1/0/1
Loopback0
10.10.10.100/32
PC
DNS Server
1.1.1.1/24
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2.1.2 DHCP Relay
The early DHCP protocol applies to the situation where the DHCP client and DHCP server are
located on the same network segment. Thus, it is necessary but uneconomical to configure a
DHCP server on each network segment to perform dynamic host configuration.
The DHCP relay function addresses the preceding problem. Through the DHCP relay function,
clients can share DHCP servers on other network segments, and thus obtain valid IP addresses.
In this manner, DHCP clients on different network segments can use the same DHCP server.
This reduces costs and implements centralized management.Figure 2-2 shows a typical
networking diagram of DHCP relay.
Figure 2-2 Typical networking diagram of the DHCP relay agent
DHCP Server A
10.10.10.1/24
Internet
DHCP Server B
10.10.10.2/24
Switch
DHCP Relay
GE1/0/1
DHCP
Client
VLANIF100
20.20.20.1/24
DHCP
Client
DHCP
Client
VLAN100
2.1.3 DHCP Proxy
To manage DHCP users, the S9300 provides the DHCP proxy function. DHCP proxy manages
users as follows:
l
DHCP proxy authenticates and authorizes access users with the local, remote (RADIUS or
HWTACACS), and non-authentication policies.
l
After the status of access users becomes normal, DHCP proxy is able to manage the
specified user, for example, performs re-authentication, re-authorization, and accounting
and forces users offline.
Figure 2-3 shows a typical networking diagram of DHCP proxy.
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Figure 2-3 Typical networking diagram of DHCP proxy
DHCP
Server
10.10.10.10
Radius
Multicast
Server
Router
Switch
LoopBack0
10.10.10.100/32
GE 1/0/1.100
GE 1/0/2.100
STB-A
STB-B
2.1.4 Procedure for Obtaining the IP Address from the DHCP Server
or the DHCP Relay Agent
Figure 2-4 shows the procedure for obtaining the IP address from the DHCP server or the DHCP
relay agent.
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Figure 2-4 Procedure for obtaining the IP address from the DHCP server or the DHCP relay
agent
DHCP messages
DHCP protocol stack
DHCP message parsing
DHCP Server
AM module allocates
IP addresses
Send Offer
messages
Send ACK
messages
DHCP Relay
Select the DHCP
server
Send messages
The procedure for obtaining the IP address from the DHCP server is as follows:
1.
The client broadcasts a DHCP DISCOVER packet and only DHCP servers replies to the
packet.
2.
After receiving the DHCP DISCOVER packet from the client, each DHCP server selects
an unassigned IP address from the IP address pool, and then sends a DHCP OFFER packet
with information about the leased IP address and other settings to the client.
3.
If multiple DHCP servers send DHCP OFFER packets to the client, the client accepts the
first received DHCP OFFER packet, and then broadcasts a DHCP REQUEST packet
carrying information about the selected IP address.
4.
After receiving the DHCP REQUEST packet, the DHCP server sends a DHCP ACK packet
to the client. The DHCP ACK packet contains the offered IP address and other settings.
5.
After the user obtains the IP address with the lease, the user access link is set up. Before
the IP address lease expires, the user applies for extending the IP address lease. After being
permitted by the local address pool or the DHCP server, the IP address lease of the user is
extended. Otherwise, the user is forcibly disconnected from the network when the IP
address expires. Then the user obtains the IP address according to the preceding procedure.
The procedure for obtaining the IP address from the DHCP relay agent is as follows:
1.
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a DHCP DISCOVER packet, on the local network. If there is no DHCP server on the local
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network, the device that is enabled with the DHCP relay function and is connected to the
local network processes the received broadcast packet and forwards the packet to the
corresponding DHCP server on another network.
2.
The DHCP server configures the parameters contained in the received packet and sends
the configuration to the DHCP client through the DHCP relay agent.
3.
The DHCP client replies to the DHCP OFFER packet sent by the server by broadcasting a
DHCP REQUEST packet through the DHCP relay agent.The DHCP relay agent sends the
DHCP REQUEST packet in unicast mode to the DHCP server.
4.
The DHCP server responds with a unicast DHCP ACK or DHCP NAK packet to the client
through the DHCP relay agent.
5.
After the user obtains the IP address with the lease, the user access link is set up. Before
the IP address lease expires, the user applies for extending the IP address lease. After being
permitted by the local address pool or the DHCP server, the IP address lease of the user is
extended. Otherwise, the user is forcibly disconnected from the network when the IP
address expires. Then the user obtains the IP address according to the preceding procedure.
2.1.5 DHCP Proxy Procedure
Figure 2-5 shows the DHCP proxy procedure.
Figure 2-5 DHCP proxy procedure
Client
terminal
DHCPR
DHCPS
UCM
AAA
AM
Discovery
message
Create user
MAC Hush entry
Connection
request
Create user
entry
User
authentication
request
User authentication request
CM connection response
contains pool number
User authentication response
Forward Discovery Apply address and gateway by pool number
Respond Offer
Allocate available address from address pool
Offer message
Request message
ACK message
Forward Request
Respond ACK
Address renew or confirm request
Address application succeeds
Connection Up
User obtains
IP address
User goes
online
The procedure for the DHCP proxy user to go online is as follows:
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1.
After receiving DHCP Discovery or DHCP Request messages of the user, the DHCPR
module sends connection setup requests to the UCM module.
2.
The UCM module determines whether to permit the connection setup and allocate entries.
Then the UCM module notifies the AAA module for authentication. The AAA module
performs local authentication or notifies the RADIUS module for remote authentication.
After AAA authentication ends, the AAA module notifies the UCM module of
authentication results.
3.
After receiving authentication response, the UCM module sends authentication connection
setup information containing the address pool gateway and DHCP server to the DHCPR
module.
4.
The DHCPR module applies to the local or remote DHCP server for the IP address. After
receiving the IP address allocated by the server, the DHCPR module notifies the UCM
module that the connection is Up. Then the UCM module sends user entries through the
TM module.
5.
After receiving the response of successfully sending entries, the UCM module notifies the
ARP module of performing online detection. The UCM module sends ACK messages about
the connection being Up to the DHCPR module after receiving online detection response
of the ARP module. The DHCPR module sends DHCP ACK messages to the user. Then
the user goes online.
6.
The UCM module notifies the AAA module of starting accounting. After receiving the
remote accounting response, the AAA notifies the UCM module. After receiving the
accounting response message of the AAA module, the UCM module processes the
remaining duration or traffic in the response message and clears accounting failure counters
if the accounting succeeds. The UCM module uses the policy for accounting start failures
if the accounting fails.
2.2 Troubleshooting of the DHCP Server Based on the
Global Address Pool
This section describes the notes about configuring the DHCP server, and provides the DHCP
snooping troubleshooting flowchart and the troubleshooting procedure in a typical networking
of the DHCP server based on the global address pool.
2.2.1 Typical Networking
2.2.2 Configuration Notes
2.2.3 Troubleshooting Flowchart
2.2.4 Troubleshooting Procedure
2.2.1 Typical Networking
Figure 2-6 shows the typical networking of the DHCP server. Troubleshooting of the DHCP
server based on the global address pool is based on this networking.
In Figure 2-6, the DHCP client and DHCP server are located on the same LAN and are connected
through GigabitEthernet 1/0/1.
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Figure 2-6 Typical networking of the DHCP server
DHCP Clients
DHCP Server
GE1/0/1
VLANIF100
DHCP Clients
2.2.2 Configuration Notes
Item
Subitem
Configuration Notes and Commands
Configuring
the global
address pool
Configuring an
IP address pool
The DHCP server assigns an IP address to a DHCP client
by using an address pool.
To configure an IP address pool, run the following
commands in sequence in the related views: dhcp enable
(system view)
dhcp select global (interface view)
ip pool ip-pool-name (system view)
Setting the
range of IP
addresses in the
IP address pool
To set the range of IP addresses in the IP address pool, run
the network ip-address [ mask { mask | mask-length } ]
command in the IP address pool view.
Setting the
address lease
Different address pools can have different IP address leases
on the DHCP server, whereas IP addresses in one address
pool have the same lease. By default, the IP address lease
is one day.
To set the address lease, run the lease { day day [ hour
hour [ minute minute ] ] | unlimited } command in the IP
address pool view.
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Item
Subitem
Configuration Notes and Commands
Configuring
static
binding
between IP
addresses
and MAC
addresses
Binding an IP
address to a
MAC address
When a user needs a fixed IP address, you can bind an idle
IP address in the IP address pool to the MAC address of the
user. After the IP address is bound to the MAC address of
the user, the lease of the IP address does not expire and the
IP address cannot be deleted when the user is using the IP
address.
Before binding an IP address to a MAC address, you need
to perform the task of Configuring the Egress Gateway of
the DHCP Client.
To bind an IP address to a MAC address, run the staticbind ip-address ip-address mac-address mac-address
command in the IP address pool view.
2.2.3 Troubleshooting Flowchart
As shown in Figure 2-6, if a client cannot obtain an IP address after the global address pool is
configured, rectify the fault according to Figure 2-7.
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Figure 2-7 Troubleshooting flowchart of the DHCP server based on the global address pool
The client cannot acquire
an IP address
Is the physical
connection with the
server in good
shape
Yes
No
Ensure that the
physical connection
is in good shape
Is fault
rectified
Yes
No
Is fault
rectified
Enable the DHCP service
Yes
No
Is the global address
pool configured
No
Configure the
global address
pool
Is fault
rectified
Yes
No
Yes
No Modify either of
Does the address in the
the addresses to
address pool have the
ensure that they
same network segment as
the IP address of the
are the same
interface
Is fault
rectified
Yes
No
Yes
Configure the client to
acquire the IP address from
the global address pool
Is fault
rectified
Yes
No
Does the address
pool have free
addresses
Yes
No
Does the address
pool have expired
addresses
Seek
technical
support
Yes
No
Does the address
pool have conflicting
addresses
No
Re-establish the
global address
pool
Is fault
rectified
No
Yes
Release conflicting
addresses
Yes
Is fault
rectified
No
Seek
technical
support
Yes
End
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2.2.4 Troubleshooting Procedure
Procedure
Step 1 Check that the physical connection is normal.
Set the IP address of the network adapter of the client connected to the DHCP server and ensure
that the IP address of the network adapter of the DHCP client and the IP address of VLANIF
100 interface are located on the same network segment. Ping the IP address of VLANIF 100
interface from the DHCP client. If the ping operation succeeds, it indicates that the physical
connection is normal.
You can also enable DHCP debugging on the server to check whether the server receives DHCP
Discover messages of the DHCP client.
Step 2 Check that the DHCP server is configured correctly.
The steps are as follows:
1.
Run the dhcp enable command to enable DHCP.
2.
Run the display ip pool all command to check whether a global address pool is created
and whether the IP address in the global address pool and the IP address of VLANIF 100
interface are located on the same network segment.
3.
l
If the global address pool is not created, run the ip pool ip-pool-name and network ipaddress [ mask { mask | mask-length } ] commands to create an IP address pool and set
the range of IP addresses that can be dynamically allocated in the IP address pool. If
the DHCP client cannot obtain an IP address, perform step c.
l
If the IP address pool is created, but IP addresses in the IP address pool and the IP
address of VLANIF 100 interface are located on different network segments, modify
either of them to ensure that both of them are located on the same network segment. If
the DHCP client cannot obtain an IP address, perform step c.
l
If the IP address pool is created and IP addresses of the IP address pool and the IP
address of VLANIF 100 interface are located on the same network segment, perform
step c.
Run the dhcp select global command on VLANIF 100 interface to ensure that the DHCP
client obtains an IP address from the global address pool. If the DHCP client cannot obtain
an IP address, proceed to step 3.
Step 3 Check whether the global address pool has available IP addresses, expired IP addresses, or
conflicting IP addresses.
The steps are as follows:
1.
Run the display ip pool used command to check whether the global address pool has
available IP addresses according to used IP addresses in the IP address pool. If yes, contact
Huawei technical personnel.
2.
If not, run the display ip pool expired command to check whether the global address pool
has expired IP addresses. If yes, contact Huawei technical personnel.
3.
If not, run the display ip pool conflict command to check whether the global address pool
has conflicting IP addresses.
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l
If not, it indicates that all the IP addresses in the address pool are used. In this case, you
can create a global address pool containing the network segment of the previous one
but with more IP addresses.
l
If yes, run the reset_ip_pool conflict command to release the conflicting IP addresses.
If the fault persists, contact Huawei technical personnel.
----End
2.3 DHCP Relay Troubleshooting
This section describes the notes about configuring DHCP relay, and provides the DHCP relay
troubleshooting flowchart and the troubleshooting procedure in a typical DHCP relay
networking.
2.3.1 Typical Networking
2.3.2 Configuration Notes
2.3.3 Troubleshooting Flowchart
2.3.4 Troubleshooting Procedure
2.3.1 Typical Networking
Figure 2-8 shows the typical networking of DHCP relay. DHCP relay troubleshooting is based
on this networking.
Figure 2-8 Typical networking of DHCP relay
DHCP Clients
DHCP Relay
GE1/0/1
VLANIF100
10.110.1.1/16
GE1/0/3
VLANIF101
20.110.1.1/16
GE1/0/2
VLANIF101
20.110.1.2/16
DHCP Server
In Figure 2-8:
2-12
l
The DHCP client and the DHCP server are located on different LANs and are connected
through the DHCP relay agent.
l
GigabitEthernet 1/0/1 of the DHCP relay agent is connected to the DHCP client. VLANIF
100 interface is enabled with the DHCP relay function and the DHCP server address is
configured on VLANIF 100 interface.
l
GigabitEthernet 1/0/2 of the DHCP relay agent is connected to GigabitEthernet 1/0/3 of
the DHCP server. Assume that the DHCP client is located on 10.110.0.0 and the DHCP
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server is located on 20.110.0.0. The DHCP server needs to allocate an IP address on
10.110.0.0 to the DHCP client through the DHCP relay agent.
2.3.2 Configuration Notes
Item
Subitem
Configuration Notes and Commands
Configuring DHCP
relay
Enabling DHCP
relay
After DHCP relay is enabled, a VLANIF
interface sends a DHCP message whose
destination IP address is the local IP address
to the external DHCP server. Then the external
DHCP server allocates an IP address to the
DHCP client.
To enable DHCP relay, run the following
commands in sequence in the related views:
dhcp enable (system view)
dhcp select relay (interface view)
Setting the DHCP
server address on an
interface enabled
with DHCP relay
Configuring the
DHCP server
Configuring a global
address pool
On the S9300, you can set the DHCP server
address by using the following methods:
l
Performing tasks of Configuring a DHCP
Server Group and Binding an Interface to a
DHCP Server Group
l
Running the dhcp relay server-ip ipaddress command in the VLANIF interface
view
When the DHCP relay agent is used to forward
packets, the DHCP server must be configured
with a global address pool.
To configure a global address pool, run the
following commands in sequence in the
related views: dhcp enable (system view)
dhcp select global (interface view)
ip pool ip-pool-name (system view)
2.3.3 Troubleshooting Flowchart
As shown in Figure 2-8, if a client cannot obtain an IP address through the DHCP relay agent,
rectify the fault according to Figure 2-9.
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Figure 2-9 Troubleshooting flowchart of DHCP relay
The client cannot acquire
an IP address
Is a
correct route established
between the relay and
the server?
No
Configure the
route
Is fault
rectified?
No
Yes
Does
the relay have the
address of the specified
server?
Yes
No
Set the address
of the specified
server on the
replay
Is fault Yes
rectified?
No
Is fault Yes
rectified?
Enable the DHCP
replay function
Diagnose and rectify the fault
in the router according to the
troubleshooting procedure for
the DHCP server based on
the global address pool
Is fault
rectified?
Yes
No
End
No
Seek
technical
support
2.3.4 Troubleshooting Procedure
Procedure
Step 1 Check that a reachable route exists between the DHCP relay agent and the DHCP server.
Assign 10.110.1.1 and 20.110.1.1 to VLANIF 100 interface and VLANIF 101 interface
respectively, and then run the ping 20.110.1.1 command on the DHCP relay agent and run the
ping 10.110.1.1 command on the DHCP server to check whether the IP addresses can be pinged.
If the ping operation fails, run the display ip routing-table command on the DHCP relay agent
and the DHCP server to check whether there are routing entries to each other.
If there are no routing entries to each other, run the ip route-static 0.0.0.0 0.0.0.0 20.110.1.1
and ip route-static 10.110.1.1 16 20.110.1.2 commands on the DHCP relay agent and the DHCP
server to add static routes.
If the ping operation fails, check whether the physical connection is normal.
Step 2 Check the configurations of the DHCP relay agent.
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Check that the DHCP relay agent is configured with the DHCP server address, that is, the dhcp
relay server-ip 20.110.1.1 command is used on VLANIF 100 interface.
Run the display dhcp relay all command in the system view to check whether DHCP relay is
enabled.
Step 3 Check the configurations of the DHCP server.
l
Run the display ip pool all command to check whether the global address pool is configured
and view the range of IP addresses that are dynamically allocated.
l
Check whether the network segment where dynamically assigned IP addresses is located is
the same as the network segment where the IP address of VLANIF 100 interface is located.
In this example, you need to check whether the network segment is configured as network
10.110.0.0 mask 255.255.0.0.
Step 4 Check that available IP addresses exist in the address pool.
l
Run the display ip pool used command to check whether the global address pool has
available IP addresses according to used IP addresses in the IP address pool.
l
If not, run the display ip pool expired command to check whether the global address pool
has expired IP addresses.
l
If not, run the display ip pool conflict command to check whether the global address pool
has conflicting IP addresses.
After the preceding steps, if there are no available IP addresses, expired IP addresses, or
conflicted IP addresses in the address pool, it indicates that all IP addresses in the address pool
are used. In this case, you can create an IP address pool containing the network segment of the
previous one but with more addresses.
If there are available IP addresses in the address pool, and the configurations and physical links
are normal, but the client cannot obtain an IP address, contact Huawei technical personnel.
----End
2.4 Troubleshooting Cases
This section presents the troubleshooting cases.
2.4.1 IP Address Assigned by the DHCP Server to a DHCP Client Conflicts with That of Another
DHCP Client
2.4.2 DHCP Client Cannot Obtain an IP Address from the DHCP Server
2.4.3 DHCP Client Cannot Obtain an IP Address Through the DHCP Relay Agent
2.4.1 IP Address Assigned by the DHCP Server to a DHCP Client
Conflicts with That of Another DHCP Client
Fault Symptom
After a client obtains an IP address from the DHCP server, information about IP address conflict
is displayed when the client uses the IP address. Figure 2-10 shows the networking.
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Figure 2-10 Conflict of the IP addresses obtained from the DHCP server
DHCP Clients
DHCP Server
GE1/0/1
VLANIF100
DHCP Clients
Fault Analysis
A user on a network may set the IP address the same as the IP address allocated by the DHCP
server to a host. As a result, IP addresses conflict.
Procedure
Step 1 Disable the network adapter of the client and ping the IP address of the DHCP client from another
host to check whether the host with this IP address exists.
Step 2 If a response message is received, it indicates that the IP address has been statically configured
by another user.
Step 3 Enable the network adapter of the client. In the Windows 98 operating system, run the
winipcfg command to release the IP address, and then apply for a new IP address. In the Windows
XP or Windows 2000 operating system or the DOS environment, run the ipconfig/release
command to release the IP address, and then apply for a new IP address.
----End
Example
After the preceding configurations are completed, the DHCP client can successfully apply for
an IP address, and the fault is thus rectified.
Summary
IP address conflict often occurs on a network. The cause is that another user on the network is
configured with the same IP address.
If IP addresses conflict, run the ipconfig/release command on the client to release the IP address,
and then run the ipconfig/renew command to apply for a new IP address. The DHCP server
preferentially allocates the originally conflicting IP address. The conflicting IP address is added
to the conflicting table when ICMP detects the conflict, and is not allocated in one hour. Then
the DHCP server allocates a new IP address to the client.
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2.4.2 DHCP Client Cannot Obtain an IP Address from the DHCP
Server
Fault Symptom
As shown in Figure 2-11, after the global address pool is configured on the DHCP server, a
client cannot obtain an IP address.
Figure 2-11 Networking where a DHCP client cannot obtain an IP address from the DHCP
server
DHCP Clients
DHCP Server
GE1/0/1
VLANIF100
DHCP Clients
Fault Analysis
The possible causes are as follows:
l
DHCP is disabled.
l
The global address pool and the IP address of GigabitEthernet 1/0/1 are located on different
network segments.
l
The physical link is faulty.
Procedure
Step 1 Run the display ip pool all command. It is found that the global address pool is configured, with
the network segment being 1.1.1.0 and the subnet mask being 255.255.0.0.
Step 2 Run the interface gigabitethernet 1/0/1 command in the system view to enter the view of
GigabitEthernet 1/0/1.
Step 3 Run the display this command. It is found that the IP address of GigabitEthernet 1/0/1 is 2.2.2.2.
That is, the IP address of GigabitEthernet 1/0/1 and the global address pool are located on
different network segments.
Step 4 Run the ip address 1.1.1.1 16 command in the interface view to change the IP address of
GigabitEthernet 1/0/1 to 1.1.0.0. You can also change the network segment in the global address
pool to be the network segment where the IP address of GigabitEthernet 1/0/1 is located.
----End
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Example
After the preceding configurations are completed, the DHCP client can successfully apply for
an IP address, and the fault is thus rectified.
Summary
On a network where a client is directly connected to the DHCP server, when the global address
pool is used for IP address allocation, the global address pool and the IP address of
GigabitEthernet 1/0/1 must be located on the same network segment.
2.4.3 DHCP Client Cannot Obtain an IP Address Through the
DHCP Relay Agent
Fault Symptom
As shown in Figure 2-12, the DHCP client cannot obtain an IP address through the DHCP relay
agent.
Figure 2-12 Networking where a DHCP client cannot obtain an IP address through the DHCP
relay agent
DHCP Clients
DHCP Relay
GE1/0/1
VLANIF100
10.110.1.1/16
GE1/0/3
VLANIF101
20.110.1.1/16
GE1/0/2
VLANIF101
20.110.1.2/16
DHCP Server
Fault Analysis
1.
Run the display ip pool all command to check that the DHCP server is configured with an
address pool on the network segment where the DHCP client resides.
2.
Run the display ip interface brief command to view the configuration of the DHCP relay
agent and the DHCP server. Then you can check whether each interface is configured with
the correct IP address.
3.
Run the display dhcp relay all command to check that the interface enabled with the DHCP
replay function is configured with the DHCP server address.
4.
On the DHCP relay agent, run the ping 20.110.1.1 command. You can find that the ping
operation succeeds. On the DHCP server, run the ping 10.110.1.1 command. You can find
that the ping operation succeeds. This indicates that the route is correct.
Check the networking to check whether more than four DHCP relay agents are configured.
In the troubleshooting case, the number of DHCP relay agents is within the limit.
5.
2-18
Run the debugging dhcp server packet command to enable DHCP debugging on the
DHCP server. Then you can find that the DHCP server does not receive any DHCP Discover
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message from the DHCP client. Run the debugging dhcp relay packet command to enable
DHCP debugging on the DHCP relay agent. Then you can find that the DHCP relay agent
receives the DHCP Discover message from the DHCP client. It is inferred that the DHCP
relay agent does not forward the DHCP Discover message.
Check the configurations of the DHCP relay agent, and you can find that the dhcp select
relay command is not used. As a result, the DHCP relay function does not take effect.
Procedure
Step 1 Check that the DHCP server is configured with an address pool on the network segment where
the DHCP client resides.
Step 2 Check that the interface on the DHCP relay agent that is connected to the DHCP client is
configured with the corresponding DHCP server address. Check that no IP address conflict
occurs because multiple corresponding DHCP server addresses are configured.
Step 3 Check that the DHCP relay function is enabled.
Step 4 Check that the DHCP relay agent and the DHCP server are configured with reachable routes.
Step 5 Check the DHCP configurations to check that less than four DHCP relay agents are configured.
Step 6 Check whether the interface is enabled with the DHCP relay function. If not, run the dhcp select
relay command in the view of GigabitEthernet 1/0/1.
----End
Example
After the preceding configurations are completed, the DHCP client can successfully apply for
an IP address, and the fault is thus rectified.
Summary
When a DHCP client applies to the DHCP server for an IP address through the DHCP relay
agent, the DHCP server must be configured with the IP address pool on the network segment
where the IP address of the DHCP client is located. In addition, the IP address of the interface
enabled with the DHCP relay function must be located on the network segment where the IP
address of the DHCP client is located.
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3
DHCPv6 Troubleshooting
About This Chapter
This section describes the DHCPv6 troubleshooting flowchart and the troubleshooting procedure
in a typical DHCP relay networking and presents troubleshooting cases.
3.1 DHCPv6 Relay Troubleshooting
This section describes the notes about configuring DHCPv6 relay, and provides the DHCPv6
relay troubleshooting flowchart and the troubleshooting procedure in a typical DHCPv6 relay
networking.
3.2 Troubleshooting Cases
This section presents a troubleshooting case of DHCPv6.
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3.1 DHCPv6 Relay Troubleshooting
This section describes the notes about configuring DHCPv6 relay, and provides the DHCPv6
relay troubleshooting flowchart and the troubleshooting procedure in a typical DHCPv6 relay
networking.
3.1.1 Troubleshooting Flowchart
3.1.2 Troubleshooting Procedure
3.1.1 Troubleshooting Flowchart
Clients cannot obtain IPv6 addresses through the DHCPv6 relay agent. To rectify the fault,
follow the troubleshooting flowchart shown in Figure 3-1.
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Figure 3-1 DHCPv6 relay troubleshooting flowchart
Clients cannot obtain
IPv6 addresses
through DHCPv6 relay
Is user interface
added to correct
VLAN?
No
Add user
interface to
correct VLAN
Yes
Is
DHCP enabled
globally?
No
Enable DHCP
Yes
Is there IPv6 license?
No
Apply for the
IPv6 license
Yes
Is IPv6 enabled
globally?
No
Enable IPv6
Yes
Is IPv6 enabled
on an interface?
No
Enable IPv6 on
an interface
Yes
Is DHCPv6 relay
enabled on an
interface?
No
Enable DHCP
relay on an
interface
Yes
Can
device and server be
pinged?
No
Troubleshoot
link problem
Yes
Is fault rectified?
No
Yes
End
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technical
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3.1.2 Troubleshooting Procedure
Procedure
Step 1 Check that the user interface is added to a specified VLAN.
If the user interface is not added to a specified VLAN, user packets may be forwarded incorrectly
or discarded. If user packets are not forwarded to the DHCP server, users cannot obtain IPv6
addresses.
Step 2 Check whether DHCP is enabled globally.
[Quidway] display this
#
dhcp enable
#
Return
If DHCP is not enabled globally, the Switch does not process DHCPv6 messages sent by users.
Step 3 Run the display license command to check whether there is the IPv6 license. The IPv6 function
of the Switch is controlled by the license.
NOTE
Generally, the IPv6 commands can be run on a new device, but the corresponding IPv6 functions cannot
take effect. To make the IPv6 functions effective on the Switch, contact local office of Huawei to buy the
license.
Step 4 Check whether IPv6 is enabled. If IPv6 is not enabled, the Switch does not forward IPv6 packets.
[Quidway] display this
#
ipv6
#
Return
Step 5 Check whether IPv6 is enabled on the VLANIF interface. If IPv6 is not enabled on the VLANIF
interface, the IPv6 address cannot be set on the VLANIF interface.
Step 6 Check whether DHCPv6 relay is enabled on the VLANIF interface. If DHCPv6 relay is not
enabled on the VLANIF interface, DHCPv6 users cannot obtain IPv6 addresses in another
network segment.
Method 1: Run the display this command on the VLANIF interface connected to the client to
check whether the dhcpv6 relay destination command is used on the VLANIF interface.
[Quidway-Vlanif10] display this
#
interface Vlanif10
ipv6 enable
ipv6 address 1:2::3:4/36
dhcpv6 relay destination 2:1::3:2
#
Return
Method 2: Run the display dhcpv6 relay command in the system view on the Switch to check
whether the configuration of the interface enabled with DHCPv6 relay is correct.
[Quidway] display dhcpv6 relay
Interface
Mode
Destination
Vlanif10
Relay
2:1::3:2
Run the dhcpv6 relay destination command to enable DHCPv6 relay on the VLANIF interface
and set the IPv6 address of the DHCPv6 server or next-hop relay agent. Before running the
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dhcpv6 relay destination command, you must enable DHCP globally. Otherwise, the
configuration cannot be performed.
If the configuration fails, check whether the interface is configured with eight destination
addresses. On the Switch, up to eight interfaces can be enabled with DHCPv6 relay and each
interface can be configured with up to eight destination addresses.
If the configured IPv6 address is a global address or a site address, the outbound interface does
not need to be specified. The DHCPv6 server sends relay messages to the IPv6 address by
searching for a route. If the configured IPv6 address is a local address or a multicast address,
the outbound interface of the DHCPv6 server needs to be specified.
Step 7 Check that the user gateway and the DHCPv6 server can ping each other.
l
Ping the DHCPv6 server from the IPv6 address of the VLANIF interface enabled with DHCP
relay. If the ping operation fails, it indicates that the physical link between the Switch and
the DHCPv6 server is faulty. In this case, the DHCPv6 server cannot allocate addresses to
users on the Switch.
l
Ping the IPv6 address of the VLANIF interface enabled with DHCP relay from the DHCPv6
server. If the ping operation fails, it indicates that the physical link between the Switch and
the DHCPv6 server is faulty. In this case, the DHCPv6 server cannot allocate addresses to
users on the Switch.
Check whether physical links between the DHCPv6 client and the DHCPv6 relay agent and
between the DHCPv6 relay agent and the DHCPv6 server are faulty and locate faults.
If the fault persists, contact Huawei technical personnel.
----End
3.2 Troubleshooting Cases
This section presents a troubleshooting case of DHCPv6.
3.2.1 Clients Cannot Obtain IPv6 Addresses Through DHCPv6 Relay
3.2.1 Clients Cannot Obtain IPv6 Addresses Through DHCPv6
Relay
Fault Symptom
As shown in Figure 3-2, the Switch functions as the DHCPv6 relay agent. It is found that clients
cannot obtain IPv6 addresses.
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Figure 3-2 Networking where clients cannot obtain IPv6 addresses
DHCPv6 client
DHCPv6 client
GE1/0/2
GE1/0/1
Switch
VLANIF20
VLANIF10
3000::1/64
2000::1/64
DHCPv6 relay agent
3000::3/64
DHCPv6 server
DHCPv6 client
DHCPv6 client
Fault Analysis
The possible causes are as follows:
l
VLANIF 10 is not enabled with DHCPv6 relay.
l
IPv6 addresses of VLANIF 20 and the DHCPv6 server interface address are in different
network segments.
l
The physical link is faulty.
Procedure
Step 1 Check whether GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 are added to a correct VLAN.
Run the display this command on GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 to check
whether GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 are added to a correct VLAN.
[Quidway-GigabitEthernet1/0/1] display this
#
interface gigabitethernet 1/0/1
port hybrid pvid vlan 10
port hybrid untagged vlan 10
#
Return
[Quidway-GigabitEthernet1/0/2] display this
#
interface gigabitethernet 1/0/2
port hybrid pvid vlan 20
port hybrid untagged vlan 20
#
Return
Step 2 Check whether DHCP and IPv6 are enabled globally.
[Quidway] display this
#
dhcp enable
#
ipv6
#
Return
Step 3 Check whether VLANIF 10 is enabled with DHCPv6 relay.
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Run the display this command on VLANIF 10 to check whether the dhcpv6 relay
destination command is used on VLANIF 10.
[Quidway-Vlanif10] display this
#
interface Vlanif10
ipv6 enable
ipv6 address 2000::1/64
dhcpv6 relay destination 3000::3/64
#
Return
Step 4 Check whether the IPv6 address of VLANIF 20 is correctly set.
Run the display this command on VLANIF 20 to check whether IPv6 addresses of VLANIF 20
and the DHCPv server interface are in the same network segment.
[Quidway-Vlanif20] display this
#
interface Vlanif20
ipv6 enable
ipv6 address 3001::1/64
#
Return
According to the preceding output, the IPv6 address of VLANIF 20 is 3001::1/64, whereas the
IPv6 address of the DHCPv6 server interface is 3000::3/64. That is, IPv6 addresses of VLANIF
20 and the DHCPv server interface are in different network segments.
Change the IPv6 address of VLANIF 20 to 3000::1/64.
[Quidway-Vlanif20] ipv6 address 3000::1 64
----End
Example
After the preceding configuration, DHCP clients can obtain IPv6 addresses, and the fault is thus
rectified.
Summary
Ensure that IPv6 addresses of the VLANIF interface connecting the DHCPv6 relay agent and
the DHCPv6 server and the DHCPv6 server interface are in the same network segment.
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4
4 UDP Helper Troubleshooting
UDP Helper Troubleshooting
About This Chapter
This chapter describes troubleshooting of the User Datagram protocol (UDP) helper, including
the principle of UDP helper, typical networking, troubleshooting procedure, troubleshooting
cases, FAQs, and diagnostic tools.
4.1 UDP Helper Overview
This section describes the information that you need to know before troubleshooting the UDP
helper.
4.2 UDP Helper Troubleshooting
This section describes the notes about configuring the UDP helper, and provides the UDP helper
troubleshooting flowchart and the troubleshooting procedure in typical UDP helper networking.
4.3 Troubleshooting Cases
This section presents several troubleshooting cases.
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4.1 UDP Helper Overview
This section describes the information that you need to know before troubleshooting the UDP
helper.
A UDP helper functions as a relay to forward the broadcast UDP packets with specified
destination port numbers. It converts the broadcast UDP packets to unicast UDP packets and
sends them to the specified server. The UDP helper can forward broadcast packets from a subnet
to another subnet.
4.2 UDP Helper Troubleshooting
This section describes the notes about configuring the UDP helper, and provides the UDP helper
troubleshooting flowchart and the troubleshooting procedure in typical UDP helper networking.
4.2.1 Typical Networking
4.2.2 Configuration Notes
4.2.3 Troubleshooting Flowchart
4.2.4 Troubleshooting Procedure
4.2.1 Typical Networking
Figure 4-1 shows the typical networking diagram of a UDP helper. Troubleshooting of the UDP
helper is based on the networking.
Figure 4-1 Typical networking diagram of the UDP helper
Internet
VLANIF1
1.1.1.1/24
Server
1.1.1.10/32
VLANIF3
3.3.3.1/24
VLANIF2
2.2.2.1/24 Switch
Switch
VLANIF2
4-2
User2
User3
User1
2.2.2.10/32
2.2.2.11/32
3.3.3.10/32
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As shown in Figure 4-1:
l
User 2 and User 3 belong to the same VLAN 2.
l
User 1 belongs to the VLAN 3.
l
The server belongs to the VLAN 1.
User 1 periodically sends broadcast packets such as NETBIOS-NS packets to query information
about datagrams on the network.To query information about datagrams of a device in a different
VLAN, for example, Server, User 1 requires a UDP helper to forward the query packets to Server.
4.2.2 Configuration Notes
Item
Sub-item
Configuration Notes and Commands
Setting
port
numbers
for the
UDP
helper
Enabling the
UDP helper
After the UDP helper is enabled, the UDP helper takes effect for
the following UDP destination port numbers by default:
l
DNS: domain name service (53)
l
NETBIOS-DS: NETBIOS datagram service (138)
l
NETBIOS-NS: NETBIOS name service (137)
l
TACAS: Terminal Access Controller Access-Control System
(49)
l
TFTP: Trivial File Transfer Protocol (69)
l
Time Service: 37
When the UDP helper is disabled, all the configured UDP port
numbers are deleted.
To enable the UDP helper, run the udp-helper enable command
in the system view. To disable the UDP helper, run the undo
udp-helper enable command in the system view.
Setting port
numbers for
the UDP
helper
Issue 01 (2010-07-15)
The UDP helper cannot be used to relay DHCP packets. That is,
the destination port number cannot be set to 67 or 68.
You can set up to 40 UDP port numbers on the S9300.
To set a UDP port number, run the udp-helper port portnumber command in the system view. To delete a UDP port
number, run the undo udp-helper port port-number command
in the system view.
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Item
Sub-item
Configuration Notes and Commands
Configur
ing the
UDP
helper
server
Configuring
the UDP
helper server
You can configure up to 20 destination servers to which the
packets can be relayed on a VLANIF interface.
When specifying the IP address of a destination server, ensure
that the S9300 has a reachable route to the server; otherwise,
packet relay fails.
A UDP port number takes effect globally. That is, if a UDP port
number is set, all the VLANIF interfaces configured with
destination servers forward the packets with this port number.
You cannot configure a single VLANIF interface to forward
packets with the specified UDP port number.
To configure a UDP helper server, run the udp-helper server
ip-address command in the VLANIF interface view. To delete
a UDP helper server, run the undo udp-helper server ipaddress command in the VLANIF interface view.
4.2.3 Troubleshooting Flowchart
Figure 4-2 shows the flowchart of UDP helper troubleshooting.
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Figure 4-2 UDP helper troubleshooting flowchart
UDP helper is
unavailble
No
Is UDP helper
enabled?
Enable UDP helper
Yes
No
Is the fault
rectified?
No
Is UDP port
number set?
Yes
End
Set the UDP port
number
Yes
No
No
Is destination
server specified?
Is the fault
rectified?
Yes
End
Specify the destination
server
Yes
Is the fault
rectified?
Yes
End
No
Check the route
between the local
device and the server
Is the fault
rectified?
No
Seek technical
support
Yes
End
4.2.4 Troubleshooting Procedure
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Procedure
Step 1 Check and ensure that the UDP helper is enabled.
1.
Run the display this command in the system view to check whether the UDP helper is
enabled.
2.
If the UDP helper is not enabled, run the udp-helper enable command to enable it. If the
UDP helper is enabled, proceed to Step 2.
Step 2 Check and ensure that the UDP port numbers are set correctly.
1.
Run the display this command in the system view to check the UDP port numbers.
After the UDP helper is enabled, the S9300 relays the broadcast packets whose destination
port numbers are 37, 49, 53, 69, 137, and 138 by default.
2.
If the corresponding UDP port numbers are set, proceed to Step 3.
Step 3 Check and ensure that the destination server is configured.
1.
Run the display this command in the VLANIF interface to view the configuration of the
destination server.
2.
If the destination server is configured correctly, proceed to Step 4.
Step 4 Check the route between the S9300 and the destination server.
1.
Run the display ip routing-table command to check whether the routing table contains
the route to the destination server.
2.
If the route exists but the fault persists, contact Huawei technical personnel.
----End
4.3 Troubleshooting Cases
This section presents several troubleshooting cases.
4.3.1 UDP Packets Cannot Be Relayed to the Destination Server
4.3.1 UDP Packets Cannot Be Relayed to the Destination Server
Fault Symptom
On the network as shown in Figure 4-3, the UDP helper is enabled, but the function does not
take effect.
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Figure 4-3 Networking diagram of the UDP helper
Internet
VLANIF1
1.1.1.1/24
Server
1.1.1.10/32
VLANIF3
3.3.3.1/24
VLANIF2
2.2.2.1/24 Switch
Switch
VLANIF2
User2
User3
User1
2.2.2.10/32
2.2.2.11/32
3.3.3.10/32
Fault Analysis
Possible causes are as follows:
l
The UDP helper is not enabled.
l
The UDP port number is not set.
l
The destination server is not configured.
l
The route between the S9300 and the destination server is unreachable.
l
Locating the fault
Procedure
1.
Run the display this command in the system view to check whether the UDP helper
is enabled.
If the UDP helper is disabled, run the udp-helper enable command to enable it.
2.
Run the display this command in the system view to check whether the UDP port
number is set.
If the UDP port number is not set, run the udp-helper port port-number command to
set the port number.
3.
l
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Run the display this command in the VLANIF interface view, and you can find that
the IP address of the destination server is 1.1.1.11. The S9300 does not have a route
to the destination server; therefore, the UDP helper function is unavailable.
Rectifying the fault
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
4-7
4 UDP Helper Troubleshooting
Quidway S9300 Terabit Routing Switch
Troubleshooting - IP Service
1.
Run the system-view command to enter the system view.
2.
Run the interface vlanif 3 command to enter the VLANIF interface view.
3.
Run the udp-helper server 1.1.1.10 command to configure the destination server.
4.
Run the return command to return to the user view.
5.
Run the save command to save the configuration.
----End
Summary
When configuring the UDP helper, ensure that the configuration of the destination server is
correct; otherwise, the UDP helper function is unavailable.
4-8
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
Issue 01 (2010-07-15)

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