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BGP Prefix-Independent Convergence (IPv4 AF)

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The topology will be used to demonstrate this feature and the proof of function

The setup consists of 5 routers each participating in its own AS # with each router advertising its loopback 0 network into BGP (each router loopback 0 interface follow the criteria x.x.x.x/32 where x is the router number)

Checking the BGP table for the prefixes received

R1#sh ip bgp

BGP table version is 6, local router ID is 1.1.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

             r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

             x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

     Network         Next Hop           Metric LocPrf Weight Path

*> 1.1.1.1/32       0.0.0.0                 0        32768 i

*> 2.2.2.2/32       192.168.12.2             0             0 2 i

*> 3.3.3.3/32       192.168.13.3             0             0 3 i

*   4.4.4.4/32       192.168.13.3                           0 3 4 i

*>                   192.168.12.2                          0 2 4 i

*   5.5.5.5/32       192.168.13.3                           0 3 4 5 i

*>                   192.168.12.2                           0 2 4 5 i

As we can see from the output above that R1 is learning 4.4.4.4/32 and 5.5.5.5/32 from two different paths , it prefers the path through R2 because R2 has the lowest BGP router ID

R1#show ip bgp 5.5.5.5 255.255.255.255

BGP routing table entry for 5.5.5.5/32, version 6

Paths: (2 available, best #2, table default)

Advertised to update-groups:

     1

Refresh Epoch 1

3 4 5

   192.168.13.3 from 192.168.13.3 (3.3.3.3)

     Origin IGP, localpref 100, valid, external

     rx pathid: 0, tx pathid: 0

Refresh Epoch 1

2 4 5

   192.168.12.2 from 192.168.12.2 (2.2.2.2)

     Origin IGP, localpref 100, valid, external, best

     rx pathid: 0, tx pathid: 0x0

R1#show ip cef 5.5.5.5 255.255.255.255

5.5.5.5/32

nexthop 192.168.12.2 FastEthernet1/0

Through FIB, only one entry is installed which is the best route to reach that destination

Now, let us turn on prefix-independent convergence on R1

R1

R1(config)#router bgp 1

R1(config-router)#address-family ipv4 unicast

R1(config-router-af)#bgp additional-paths install

R1#sh ip bgp

BGP table version is 11, local router ID is 1.1.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

             r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

             x best-external, a additional-path, c RIB-compressed,

Origin codes: i - IGP, e - EGP, ? - incomplete

RPKI validation codes: V valid, I invalid, N Not found

     Network         Next Hop           Metric LocPrf Weight Path

*> 1.1.1.1/32       0.0.0.0                 0         32768 i

*> 2.2.2.2/32       192.168.12.2             0            0 2 i

*> 3.3.3.3/32       192.168.13.3             0             0 3 i

*b 4.4.4.4/32       192.168.13.3                           0 3 4 i

*>                   192.168.12.2                           0 2 4 i

*b 5.5.5.5/32       192.168.13.3                          0 3 4 5 i

*>                   192.168.12.2                           0 2 4 5 i

R1#sh ip bgp 5.5.5.5 255.255.255.255

BGP routing table entry for 5.5.5.5/32, version 11

Paths: (2 available, best #2, table default)

Additional-path-install

Advertised to update-groups:

     1

Refresh Epoch 1

3 4 5

   192.168.13.3 from 192.168.13.3 (3.3.3.3)

     Origin IGP, localpref 100, valid, external, backup/repair, recursive-via-connected

     rx pathid: 0, tx pathid: 0

Refresh Epoch 1

2 4 5

   192.168.12.2 from 192.168.12.2 (2.2.2.2)

     Origin IGP, localpref 100, valid, external, best , recursive-via-connected

     rx pathid: 0, tx pathid: 0x0

R1#sh ip cef 5.5.5.5 255.255.255.255 detail

5.5.5.5/32, epoch 0, flags rib only nolabel, rib defined all labels

recursive via 192.168.12.2

   attached to FastEthernet1/0

recursive via 192.168.13.3, repair

   attached to FastEthernet1/1

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