BGP Neighbors

[mohamedsalah786876171]

Please, can anyone provide me with an answer and its explanation?

As per the picture should I add AS 5 as a neighbor on router 1 to be able to reach router 4? 

Or this configuration is just enough?

configuration on router 1:

#no synchronization

#neighbor (IP of router 2) AS 1

#neighbor (IP of router 4) AS 1 

#no auto-summary

[Georg Pauwen]

Hello,

if the routers are connected as shown in the picture (in a daisy-chained setup) the only neighbor you can add on R1 is R2, because it IS the only neighbor. Either way, you still will not be able to reach R4, because R4 is in the same AS as R1 and will reject any routes coming from R1.

[mohamedsalah786876171]

So what should be done on R1 to be able to reach all routers that are in AS 1 and allow traffic to flow normally on this network? 

Thanks in Advance :)

@Georg Pauwen 

[Georg Pauwen]

Hello,

there is nothing you can do on R1. You need to change the configuration on R3 and R4:

R3

neighbor 192.168.3.x remote-as 2

R4

neighbor 192.168.3.x local-as 2

By using the 'local-as' feature, you make R3 believe that it is peering with R4 in AS2 instead of AS1.

[paul driver]

Hello @Georg Pauwen 

I would say your suggestion isn't complete, because with just the local-as command on R4, both rtrs will still show both ASNs on any advertised prefixs.

I would say also append no-prepend replace-as  so the real asn isn't advertised either on the R3-R4 and if applicable dual-as to allow R3 peer with either the valid or fake ASN

Example:

R4
neighbor 192.168.3.x local-as 2 no-prepend replace-as dual-as