iBGP - Next Hop Self

Refering  to Route Reflector

we can see  R6 and R4 dont have routes from each other

R6#

     Network          Next Hop            Metric LocPrf Weight Path

 *>  11.11.1.1/32     5.5.5.5                                0 101 i

 *>  22.22.2.2/32     5.5.5.5                                0 101 i

 *>  33.3.3.3/32      5.5.5.5                                0 101 i

 *>  55.5.5.5/32      5.5.5.5                  0             0 101 i

 *>  66.6.6.6/32      0.0.0.0                  0         32768 i

R6#

in R6 we still don't have route from R4

R4#

     Network          Next Hop            Metric LocPrf Weight Path

 *>  11.11.1.1/32     3.3.3.3                                0 101 i

 *>  22.22.2.2/32     3.3.3.3                                0 101 i

 *>  33.3.3.3/32      3.3.3.3                  0             0 101 i

 *>  44.4.4.4/32      0.0.0.0                  0         32768 i

 *>  55.5.5.5/32      3.3.3.3                                0 101 i

R4#

in R4 we still don't have route from R6

Next_Hop must be reachable to install route into routing table.

Problem ------

see in R5 ,

Sh ip bgp

    Network          Next Hop            Metric LocPrf Weight Path

  * i 44.4.4.4/32      4.4.4.4                  0    100      0 201 i

Route is not best . next hop 4.4.4.4 is unreachable

R5#sh ip route 4.4.4.4

% Network not in table

R5#

This route will not forward to any peer. R5 don't have route.

Solutions----

There are two solution .

1.Make 4.4.4.4 reachable in IGP.

2. Change Next _Hop   in the BGP which is reachable

We will configure Next Hop self command in R3 and R5  see the result..

in R3

R3(config)#router bgp 101

R3(config-router)#nei 5.5.5.5 next-hop-self .

Now in R5

R5#sh ip bgp

      Network          Next Hop            Metric LocPrf Weight Path

*>i 44.4.4.4/32      3.3.3.3                  0        100         0       201 i

Now the next hop is 3.3.3.3 , which is reachable now

And in R6

R6#sh ip bgp

    Network          Next Hop            Metric LocPrf Weight Path

 *>  11.11.1.1/32     5.5.5.5                                0 101 i

 *>  22.22.2.2/32     5.5.5.5                                0 101 i

 *>  33.3.3.3/32      5.5.5.5                                0 101 i

 *>  44.4.4.4/32      5.5.5.5                                0 101 201 i

 *>  55.5.5.5/32      5.5.5.5                  0             0 101 i

 *>  66.6.6.6/32      0.0.0.0                  0         32768 i

R 6  has all prefixes.

Same we will do in R5.

R5(config-router)#nei 3.3.3.3 next-hop-self.

R3 has 

R3#sh ip bgp

Prefix from R6. Next hop is 5.5.5.5 , reachable from R3.

.*>i 66.6.6.6/32      5.5.5.5                  0    100      0 65837 i.

now r4 has all prefixes