Difference between BGP RR client and non-client

[Venison Mogambi]

I was reading up on BGP route reflection and I read that a Route Reflector (RR) will advertise all received routes to all clients and non-clients. A RR will also advertise (or reflect) routes received from clients as well as routes received from non-clients. So I'm wondering what's the difference between a client and non-client? If a RR receives and reflects routes to/from everyone, what's the point of defining some of the peers as clients and leaving others as regular iBGP peers.

The example toplogy in the book I was reading had several iBGP peers configured in a RR cluster and one peer configured as a regular iBGP peer. The regular iBGP peer was peered with the RR. As far as I could tell, the regular iBGP peer was receiving all the same routes as the RR clients and advertising its routes to the RR, which the RR reflected to its clients. So why even bother with the client/non-client distinction?

Thanks.

[Peter Paluch · Accepted solution]

Hi Venison,

If a RR receives and reflects routes to/from everyone, what's the point  of defining some of the peers as clients and leaving others as regular  iBGP peers. 

Imagine that an RR has two clients, C1, C2, and two non-clients, N1 and N2. If an update comes from C1, RR will reflect this to C2, N1 and N2. The same would happen if C2 sent an update - it would be reflected to C1, N1 and N2.

However, if an update comes from N1, this will be reflected to C1 and C2 but not to N2. Similarly, if an update comes from N2, it will be reflected only to C1 and C2 but not to N1. This requires N1 and N2 to have their own peerings apart from the peering with the RR.

Would this help?

Best regards,

Peter

[Venison Mogambi]

Yeah, that makes sense, good explanation. Thanks for the reply.

[Venison Mogambi]

So one more thought on that - I guess the RR client relationship effectively allows you to override the BGP split-horizon rule?

[Peter Paluch]

Hello Venison,

Can you explain more precisely what do you mean by "the BGP split-horizon rule"? Although this term occurs every now and then, the BGP-4 RFC 4271 never uses that term, and so its meaning is ambiguous to me.

Best regards,

Peter