iBGP routes from clients not to be affected by outbound route-maps?

[EasonY]

Hi,

I've got below topology with RTA internally peered with RR1 and RR2 as client. RR1 and RR2 are normal iBGP peers.

I can see from RR1 the prefix received from RTA is as per below with 

RR1# show ip bgp ipv4 unicast nei 1.1.1.1 received-routes

Network Next Hop Metric LocPrf Weight Path
r>i 1.1.1.1/32 1.1.1.1 0 400 0 i

So I thought when RR1 reflects to route to RR2, the local-preference attribute will be affected by the outbound route-map configured between the two route-reflectors. I actually expected RR2 received the route from RR1 with local-preference reset to 100.

However when I check on RR2, the route 1.1.1.1/32 received from RR1 is still have local-preference unchanged.

RR2#show ip bgp ipv4 unicast neighbors 10.3.0.1 received-routes | inc 1.1.1.1
r i 1.1.1.1/32 1.1.1.1 0 400 0 i
RR2#

Would anyone be able to shed a bit light on this please? My question is if RR1 is reflecting a route from its client to an none-client peer, would local-preference attribute to be reset by the outbound route-map? Many thanks.

[Georg Pauwen · Accepted solution]

Hello,

I somewhere remember that there is an RFC (2796) that talks about path attributes on reflected routes. I can't recall if this is true for client AND non clients...

In addition, when a RR reflects a route, it should not modify the following path attributes: 

NEXT_HOP, AS_PATH, LOCAL_PREF, and MED.
Their modification could potential result in routing loops.

[EasonY]

Hi Georg,

I can see those external routes (RR1 received from other eBGP peers) reflected to RR2 with local-preference reset to 100 as per the outbound route-map instructed. This could be due to eBGP having a few other rules to avoid looping stuff.

Only the client routes reflected to RR2 still with local preference unchanged. 

Thanks very much for the explanation.

Regards

Eason