13.3.3 Checking BGP4 route selection

To check the BGP4 route selection result, use the show ip bgp operation command.

Figure 13-12: Result of executing show ip bgp command
> show ip bgp Date 20XX/10/18 22:44:23 UTC Local AS: 65531, Local Router ID: 192.168.1.100 Status Codes: d dampened, * valid, > active, S Stale, r RIB failure Origin Codes: i - IGP, e - EGP, ? - incomplete Network Next Hop MED LocalPref Weight Path > 10.10/16 172.16.2.2 - 120 20 65532 65528 i ..1 10.10/16 10.2.2.2 - 80 20 65533 65533 65529 i..2 * 10.10/16 10.1.2.2 - 80 10 65534 i ..3 > 10.20/16 172.16.2.2 - 80 20 65532 65528 i ..4 10.20/16 10.2.2.2 - 80 20 65533 65533 65529 i..5 > 172.20/16 192.168.2.2 - 100 10 65530 i ..6 172.20/16 10.1.2.2 - 100 10 65534 65530 ? ..7 > 172.30/16 10.1.2.2 - 100 10 65534 i ..8 172.30/16 192.168.2.2 100 100 10 65530 i ..9 > 192.168.10/24 10.1.2.2 - 100 10 65534 i ..10 192.168.10/24 192.168.2.2 - 100 10 65530 i ..11 > 192.169.10/24 192.168.2.2 - 100 10 i ..12 > 192.169.20/24 192.168.2.2 - 100 10 i ..13

Figure 13-12: Result of executing show ip bgp command

> show ip bgp
Date 20XX/10/18 22:44:23 UTC
Local AS: 65531, Local Router ID: 192.168.1.100
Status Codes: d dampened, * valid, > active, S Stale, r RIB failure
Origin Codes: i - IGP, e - EGP, ? - incomplete
   Network          Next Hop      MED   LocalPref Weight Path
*> 10.10/16         172.16.2.2    -     120       20     65532 65528 i      ..1
*  10.10/16         10.2.2.2      -     80        20     65533 65533 65529 i..2
*  10.10/16         10.1.2.2      -     80        10     65534 i            ..3
*> 10.20/16         172.16.2.2    -     80        20     65532 65528 i      ..4
*  10.20/16         10.2.2.2      -     80        20     65533 65533 65529 i..5
*> 172.20/16        192.168.2.2   -     100       10     65530    i         ..6
*  172.20/16        10.1.2.2      -     100       10     65534 65530 ?      ..7
*> 172.30/16        10.1.2.2      -     100       10     65534 i            ..8
*  172.30/16        192.168.2.2  100    100       10     65530 i            ..9
*> 192.168.10/24    10.1.2.2      -     100       10     65534 i           ..10
*  192.168.10/24    192.168.2.2   -     100       10     65530 i           ..11
*> 192.169.10/24    192.168.2.2   -     100       10           i           ..12
*> 192.169.20/24    192.168.2.2   -     100       10           i           ..13

1 to 3. Route selection of 10.10/16: Routes 1 and 2 are preferred by comparing the weights of the three routes, and then 1 is selected by comparing the LOCAL_PREF values of 1 and 2.
4-5. 10.20/16 Route Selection: Route 4 is selected by comparing the AS_PATH length of each route.
6-7. 172.20/16 Route Selection: Route 6 is selected by comparing the ORIGIN attribute of each route.
8-9. 172.30/16 Route Selection: Route 8 is selected by comparing the MED attribute of each route.
10 to 11. 192.168.10/24 route selection: Route 10 is selected by comparing the peer BGP identifier of each route.
12 to 13. 192.169.10/24, 192.169.20/24 route selection: Route 12 and route 13 are selected because there are no other routes to the destinations.