Example for Configuring a Device to Obtain Forwarded Packet Headers

This section provides an example for configuring a device to obtain forwarded packet headers.

Networking Requirements

As shown in Figure 1, PC1 accesses the Internet over Device A and Device B. Video quality on PC1 deteriorates, which may be caused by a fault that occurred on Device B. To find out the reason why video quality deteriorates, configure Device A to obtain packet headers forwarded by Device B to the inbound interface GE 0/1/0 of Device A.

Figure 1 Configuring Device A to obtain forwarded packet headers

Interfaces 1 through 3 in this example represent GE 0/1/0, GE 0/1/1 and GE 0/1/2, respectively.

Configuration Roadmap

The configuration roadmap is as follows:

Configure an access control list (ACL) rule.
Configure Device A to obtain forwarded packet headers.

Data Preparation

To complete the configuration, you need the following data:

Interface IP addresses
ACL number
Packet header obtaining timeout time, number of obtained packet headers, and packet header obtaining file name

Procedure

Configure interface IP addresses and routing protocol. The configuration details are not provided.

Configure an ACL rule.

<DeviceA> system-view
[DeviceA] acl number 2001
[DeviceA-acl4-basic-2001] rule permit source 10.1.1.1 0.0.0.0
[DeviceA-acl4-basic-2001] commit
[DeviceA-acl4-basic-2001] quit
[DeviceA] quit

Configure Device A to obtain forwarded packet headers.

<DeviceA> capture-packet forwarding interface gigabitethernet 0/1/0 inbound acl 2001 time-out 3600 packet-len 62 packet-num 900

View the configuration and the packet header obtaining file.

# View the configuration.

<DeviceA> display capture-packet config-state
Capture-Packet Index 1
Type        : forwarding
Interface   : GigabitEthernet
Direction   : inbound
ACL         : 2001
File Name   : cfcard:/capture_fwd_GigabitEthernet3.0.0_2012-05-03-14-25-42.cap
Time-out    : 3600 seconds
Packet-num  : 900
Packet-len  : 62
BufferOnly  : disabled

# View the packet header obtaining file.

<DeviceA> display capture-packet file cfcard:/capture_fwd_GigabitEthernet3.0.0_2012-05-03-14-25-42.cap
a1 b2 c3 d4 00 02 00 04 00 00 00 00 00 00 00 00
00 00 ff ff 00 00 00 09 4d 10 36 db 00 0a d5 81
00 00 00 0c 00 00 00 0c ff 03 c0 21 09 9d 00 08
8a 8c bc c3 4d 10 36 db 00 0a d6 ae

Configuration Files

Device A configuration file

#
sysname DeviceA
#
acl number 2001
 rule 5 permit source 10.1.1.1 0
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 10.1.1.2 255.255.255.0
#
interface GigabitEthernet0/1/1
 undo shutdown
 ip address 10.1.2.1 255.255.255.0
#
ospf 1
 area 0.0.0.0
  network 10.1.1.0 0.0.0.255
  network 10.1.2.0 0.0.0.255
#
return

Device B configuration file

#
sysname DeviceB
#
interface GigabitEthernet0/1/0
 undo shutdown
 ip address 10.1.1.1 255.255.255.0
#
interface GigabitEthernet0/1/2
 undo shutdown
 ip address 10.1.5.1 255.255.255.0
#
ospf 1
 area 0.0.0.0
  network 10.1.1.0 0.0.0.255
  network 10.1.5.0 0.0.0.255
#
return