BGP Route Reflection

Yellow indicate the iBGP peer now lets form the iBGP peer.

R2#sh ip bgp su

BGP router identifier 150.2.2.2, local AS number 100

BGP table version is 16, main routing table version 16

9 network entries using 1053 bytes of memory

9 path entries using 468 bytes of memory

4/3 BGP path/bestpath attribute entries using 496 bytes of memory

3 BGP AS-PATH entries using 72 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 2089 total bytes of memory

BGP activity 10/1 prefixes, 10/1 paths, scan interval 60 secs

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd

150.1.1.1       4   100     338     334       16    0    0 05:31:06        3

150.3.3.3       4   100     343     333       16    0    0 05:30:41        6

So we formed the iBGP peer as given above. Now lets check the router propagation

R3#sh ip bgp ne 150.2.2.2 advertised-routes

BGP table version is 13, local router ID is 150.3.3.3

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

              r RIB-failure, S Stale

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

   Network          Next Hop            Metric LocPrf Weight Path

*> 4.1.0.0/24       155.1.34.4               0             0 400 i

*> 4.2.0.0/24       155.1.34.4               0             0 400 i

*> 4.3.0.0/24       155.1.34.4               0             0 400 i

*> 5.1.0.0/24       155.1.35.5               0             0 500 i

*> 5.2.0.0/24       155.1.35.5               0             0 500 i

*> 5.3.0.0/24       155.1.35.5               0             0 500 i

Total number of prefixes 6

R3 advertising totally 6 prefixes to R2 as its having iBGP peer with R2. Now check whether  R1 getting these prefixes from R2.

R2#sh ip bgp ne 150.1.1.1 advertised-routes

Total number of prefixes 0

See R2 not advertising any prefixes to R1 This is because of  BGP SPLIT HORIZON

We can use Route Reflection to over come form this split horizon rule. Lets configure the R2 as Route reflection.

R2#sh run | se router bgp

router bgp 100

 no synchronization

 bgp log-neighbor-changes

 neighbor iBGP_Peer peer-group

 neighbor iBGP_Peer remote-as 100

 neighbor iBGP_Peer update-source Loopback0

 neighbor iBGP_Peer route-reflector-client

 neighbor 150.1.1.1 peer-group iBGP_Peer

 neighbor 150.3.3.3 peer-group iBGP_Peer

 no auto-summary

Now lets check whether R1 getting updates from R2.

R2#sh ip bgp ne 150.1.1.1 ad

R2#sh ip bgp ne 150.1.1.1 advertised-routes

BGP table version is 34, local router ID is 150.2.2.2

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

              r RIB-failure, S Stale

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

   Network          Next Hop            Metric LocPrf Weight Path

*>i4.1.0.0/24       155.1.123.3              0    100      0 400 i

*>i4.2.0.0/24       155.1.123.3              0    100      0 400 i

*>i4.3.0.0/24       155.1.123.3              0    100      0 400 i

*>i5.1.0.0/24       155.1.123.3              0    100      0 500 i

*>i5.2.0.0/24       155.1.123.3              0    100      0 500 i

*>i5.3.0.0/24       155.1.123.3              0    100      0 500 i

*>i6.1.0.0/16       155.1.16.6               0    100      0 600 i

*>i6.2.0.0/16       155.1.16.6               0    100      0 600 i

*>i6.3.0.0/16       155.1.16.6               0    100      0 600 i

Total number of prefixes 9

See we are advertising the prefixes to R1 .

R1#sh ip bgp

BGP table version is 31, local router ID is 150.1.1.1

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

              r RIB-failure, S Stale

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

   Network          Next Hop            Metric LocPrf Weight Path

*>i4.1.0.0/24       155.1.123.3              0    100      0 400 i

*>i4.2.0.0/24       155.1.123.3              0    100      0 400 i

*>i4.3.0.0/24       155.1.123.3              0    100      0 400 i

*>i5.1.0.0/24       155.1.123.3              0    100      0 500 i

*>i5.2.0.0/24       155.1.123.3              0    100      0 500 i

*>i5.3.0.0/24       155.1.123.3              0    100      0 500 i

*> 6.1.0.0/16       155.1.16.6               0             0 600 i

*> 6.2.0.0/16       155.1.16.6               0             0 600 i

*> 6.3.0.0/16       155.1.16.6               0             0 600 i

R1#sh ip bgp su

BGP router identifier 150.1.1.1, local AS number 100

BGP table version is 31, main routing table version 31

9 network entries using 1053 bytes of memory

9 path entries using 468 bytes of memory

4/3 BGP path/bestpath attribute entries using 496 bytes of memory

1 BGP rrinfo entries using 24 bytes of memory

3 BGP AS-PATH entries using 72 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 2113 total bytes of memory

BGP activity 16/7 prefixes, 16/7 paths, scan interval 60 secs

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd

150.2.2.2       4   100     416     418       31    0    0 00:54:21        6

155.1.16.6      4   600     414     418       31    0    0 06:46:01        3

We are getting totally  6 BGP prefixes form R2.