IBGP network broadcast towards 2nd hop

mouthpiec
Member
Posts: 43
Joined: 27 Aug 2013 10:58

IBGP network broadcast towards 2nd hop

Post by mouthpiec » 12 Oct 2017 07:45

Hi,

I have 4 routers having the same AS between them (IBGP).
Routers A1 and A2 host subnet Network A, while B1 and B2 host subnet Network B.

It was noted that A1 receives routes for subnet B from B1 while A2 receives routes for subnet B from B2.
In case link A1-B1 fails, A1 will loose all routes towards subnet B. Is there a way to receive these routes through A2?

Image

thanks in advance
sandro

silvio
Alcatel Unleashed Certified Guru
Alcatel Unleashed Certified Guru
Posts: 1177
Joined: 01 Jul 2008 10:51
Location: Germany

Re: IBGP network broadcast towards 2nd hop

Post by silvio » 13 Oct 2017 02:00

If I remember correctly in iBGP (all BGP router in same AS) this is a normal behavior. Every route will be forwarded only one hop to avoid route loopings. You need a full-mesh (connection also between a1-b2 and b1-a2) or you has to configure route reflection.
regards
Silvio

mouthpiec
Member
Posts: 43
Joined: 27 Aug 2013 10:58

Re: IBGP network broadcast towards 2nd hop

Post by mouthpiec » 13 Oct 2017 02:32

thanks @Silvio.
That is what I thought too.
It is a problem from our end to connect the As with Bs since these are located on different cities.
By route reflection you mean the following:
-B2 sends routes to A2 which in turn reflects these routes to A1?
-B1 sends routes to A1 which in turn reflects these routes to A2?

and so on?

silvio
Alcatel Unleashed Certified Guru
Alcatel Unleashed Certified Guru
Posts: 1177
Joined: 01 Jul 2008 10:51
Location: Germany

Re: IBGP network broadcast towards 2nd hop

Post by silvio » 15 Oct 2017 13:57

yes. But in this case every Router has to be route reflector for two RF clients. In my opinion this isn't the best way that all routers reflect the routes together. Normaly route reflector is used for external routes. And there is one central router that reflects the routes to the others and maybe one redundant router in a router cluster.
I think in your design a "normal" IGP like OSPF will be better...
regards
Silvio

mouthpiec
Member
Posts: 43
Joined: 27 Aug 2013 10:58

Re: IBGP network broadcast towards 2nd hop

Post by mouthpiec » 29 Nov 2017 14:40

Hi Silvio,
managed to do this using route refactors and it works great ... the only issue I have is that it chooses the route that is received first.
Do you think there is a way that I select preferred routes?

silvio
Alcatel Unleashed Certified Guru
Alcatel Unleashed Certified Guru
Posts: 1177
Joined: 01 Jul 2008 10:51
Location: Germany

Re: IBGP network broadcast towards 2nd hop

Post by silvio » 30 Nov 2017 03:07

Maybe with local-preference this is possible - but I only know this usage for eBGP:
A1> ip bgp network 172.21.12.0 255.255.255.0 local-preference 200
A2> ip bgp network 172.21.12.0 255.255.255.0 local-preference 100
I am not sure if this is a solution for you.
regards
Silvio

mouthpiec
Member
Posts: 43
Joined: 27 Aug 2013 10:58

Re: IBGP network broadcast towards 2nd hop

Post by mouthpiec » 30 Nov 2017 05:20

I will try it out and let you know the result.
thanks!

but what these command do in this case?

silvio
Alcatel Unleashed Certified Guru
Alcatel Unleashed Certified Guru
Posts: 1177
Joined: 01 Jul 2008 10:51
Location: Germany

Re: IBGP network broadcast towards 2nd hop

Post by silvio » 30 Nov 2017 06:29

example: if both A1/A2 in same AS100 (like at you). A1 connected to other AS200 (with preferece 200) and A2 connected to AS300 (with default pref 100). Behind AS200/300 there is an other AS with the destination route. Both A1 and A2 receive same route via its neighbor. With local-preference you can say that from your own AS prefered the route via A1 and AS200.
regards
Silvio

mouthpiec
Member
Posts: 43
Joined: 27 Aug 2013 10:58

Re: IBGP network broadcast towards 2nd hop

Post by mouthpiec » 12 Jan 2018 11:04

thanks silvio.
it was decided to go to another simpler routing protocol

silvio
Alcatel Unleashed Certified Guru
Alcatel Unleashed Certified Guru
Posts: 1177
Joined: 01 Jul 2008 10:51
Location: Germany

Re: IBGP network broadcast towards 2nd hop

Post by silvio » 13 Jan 2018 12:55

Good decision. I prefer not to use iBGB too :)
regards
Silvio

Locked

Return to “OmniSwitch 6850 / 6850E”