Hi, everyone! Today I’m going to introduce you that after the preference of the IBGP route is changed on the S6720EI, it is found that the preference of the IBGP route remains unchanged.
Involved Products and Versions
S series switches
running all versions
Networking
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.
Thank you!
