[All About Switches] Preference of the IBGP Route Changed Using the Preference Command Does Not Take Effect

Created: Mar 16, 2018 09:48:52Latest reply: Mar 16, 2018 17:48:16 1157 1 0 0

Involved Products and Versions

S series switches

running all versions

Networking

20180316094845605001.png

The S6720EI and S9706B are PE devices, and the S9706A is a P device.

Fault Symptom

The S9706B advertises the VPNv4 route to the S6720EI. After the preference of the IBGP route is changed on the S6720EI, it is found that the preference of the IBGP route remains unchanged.

Cause Analysis

# Display the IBGP route whose preference is not changed, and the preference is 255.

[HUAWEI-bgp-ABC]display ip routing-table vpn-instance ABC
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: ABC
         Destinations : 10       Routes : 10
Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface
        0.0.0.0/0   IBGP    255  0          RD   128.127.133.6   XGigabitEthernet0/0/1
        2.2.2.0/24  IBGP    255  0          RD   128.127.133.6   XGigabitEthernet0/0/1
128.127.133.210/31  Direct  0    0           D   128.127.133.211 XGigabitEthernet0/0/2.106
128.127.133.211/32  Direct  0    0           D   127.0.0.1       XGigabitEthernet0/0/2.106
128.127.133.220/31  IBGP    255  0          RD   128.127.133.2   XGigabitEthernet0/0/1
    192.168.2.1/32  IBGP    255  0          RD   128.127.133.2   XGigabitEthernet0/0/1
    192.168.3.1/32  IBGP    255  0          RD   128.127.133.3   XGigabitEthernet0/0/1
    192.168.6.1/32  IBGP    255  0          RD   128.127.133.6   XGigabitEthernet0/0/1
   192.168.10.1/32  IBGP    255  0          RD   128.127.133.1   XGigabitEthernet0/0/1
  192.168.149.1/32  EBGP    255  0           D   128.127.133.210 XGigabitEthernet0/0/2.106

# Run the preference command to change the preference of the IBGP route to 200.

[HUAWEI-bgp-ABC]preference ?
  INTEGER<1-255>  EBGP route preference
  route-policy    Specify a route policy
[HUAWEI-bgp-ABC]preference 20 ?
  INTEGER<1-255>  IBGP route preference
[HUAWEI-bgp-ABC]preference 20 200 ?
  INTEGER<1-255>  Local created route preference
[HUAWEI-bgp-ABC]preference 20 200 255 ?
  route-policy  Specify a route policy
  <cr>
[HUAWEI-bgp-ABC]preference 20 200 255
[HUAWEI-bgp-ABC]dis ip routing-table vpn-instance ABC
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: ABC
         Destinations : 10       Routes : 10
Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface
        0.0.0.0/0   IBGP    255  0          RD   128.127.133.6   XGigabitEthernet0/0/1
        2.2.2.0/24  IBGP    255  0          RD   128.127.133.6   XGigabitEthernet0/0/1
128.127.133.210/31  Direct  0    0           D   128.127.133.211 XGigabitEthernet0/0/2.106
128.127.133.211/32  Direct  0    0           D   127.0.0.1       XGigabitEthernet0/0/2.106
128.127.133.220/31  IBGP    255  0          RD   128.127.133.2   XGigabitEthernet0/0/1
    192.168.2.1/32  IBGP    255  0          RD   128.127.133.2   XGigabitEthernet0/0/1
    192.168.3.1/32  IBGP    255  0          RD   128.127.133.3   XGigabitEthernet0/0/1
    192.168.6.1/32  IBGP    255  0          RD   128.127.133.6   XGigabitEthernet0/0/1
   192.168.10.1/32  IBGP    255  0          RD   128.127.133.1   XGigabitEthernet0/0/1
  192.168.149.1/32  EBGP    20   0           D   128.127.133.210 XGigabitEthernet0/0/2.106

The command output shows that the preference of the IBGP route remains 255.

# Run the preference command to change the preference of the local route to 200.

[HUAWEI-bgp-ABC]preference ?
  INTEGER<1-255>  EBGP route preference
  route-policy    Specify a route policy
[HUAWEI-bgp-ABC]preference 20 ?
  INTEGER<1-255>  IBGP route preference
[HUAWEI-bgp-ABC]preference 20 255 ?
  INTEGER<1-255>  Local created route preference
[HUAWEI-bgp-ABC]preference 20 255 200 ?
  route-policy  Specify a route policy
  <cr>
[HUAWEI-bgp-ABC]preference 20 255 200
[HUAWEI-bgp-ABC]dis ip routing-table vpn-instance ABC
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: ABC
         Destinations : 10       Routes : 10
Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface
        0.0.0.0/0   IBGP    200  0          RD   128.127.133.6   XGigabitEthernet0/0/1
        2.2.2.0/24  IBGP    200  0          RD   128.127.133.6   XGigabitEthernet0/0/1
128.127.133.210/31  Direct  0    0           D   128.127.133.211 XGigabitEthernet0/0/2.106
128.127.133.211/32  Direct  0    0           D   127.0.0.1       XGigabitEthernet0/0/2.106
128.127.133.220/31  IBGP    200  0          RD   128.127.133.2   XGigabitEthernet0/0/1
    192.168.2.1/32  IBGP    200  0          RD   128.127.133.2   XGigabitEthernet0/0/1
    192.168.3.1/32  IBGP    200  0          RD   128.127.133.3   XGigabitEthernet0/0/1
    192.168.6.1/32  IBGP    200  0          RD   128.127.133.6   XGigabitEthernet0/0/1
   192.168.10.1/32  IBGP    200  0          RD   128.127.133.1   XGigabitEthernet0/0/1

The command output shows that the preference of the IBGP route is changed to 200.

The S6720EI processes the routes that are advertised by the peer S9706B or generated after route cross as the local routes. As a result, changing the preference of the IBGP route does not take effect.

Troubleshooting Procedure

Change the preference of the local route.

Conclusions and Suggestions

The type of the route that is generated after route cross must be clarified. In addition, the route generated after local route cross, to be specific, generated after route cross is performed between two VPNs on the same device, is processed as the local route, rather than the IBGP route.

This post was last edited by 交换机在江湖 at 2018-03-16 09:53.
  • x
  • convention:

WoodWood     Created Mar 16, 2018 17:48:16 Helpful(0) Helpful(0)

:)
  • x
  • convention:

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