BGP, Full Mesh and Route Reflector setup

Posted on 2014-10-18
1 Endorsement
Last Modified: 2014-10-22
Hello Experts,

We are small wisp, and have an ospf network, as attached, and now we want to do full mesh bgp and route reflection, i ahve tried to read on internet but cannot understand how full mesh is implemented and works, on the map R1 and R2 are main routers, and R3 to R9, are routers but have clients connected to them, part of our main ospf network. This is just an example but we have like 30 routers, with clients on them and connected by various links, wireless and fiber so multiple link to each router.

If i do full mesh bgp, how do i link all these up ?

Any pointers ?

Many thanks for the time.
Question by:skywalker7
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LVL 29

Expert Comment

by:Jan Springer
ID: 40388961
That's a lot of overhead.

Typically, I configure eBGP on each router to its external peer and all routers with eBGP peering sessions have an iBGP session between each other.

Everything else is OSPF.

You have 9 eBGP peering sessions?

Author Comment

ID: 40389304
At the moment all is osfp, I just want to start to configure ibgp on these routers as full mesh, but have no idea on which routers to configure and how to peer to each other.

LVL 29

Assisted Solution

by:Jan Springer
Jan Springer earned 100 total points
ID: 40389546
You configure BGP with our upstream providers.

You configure BGP between all of your routers that have eBGP peers.

Send default routes downstream to all other routers.
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Author Comment

ID: 40389685
Thank you for the response, at the moment I am not doing bgp with upstream, and i only want to do full bgp mesh where later i can do route reflect, after that i can do bgp with my clients who are connected to me with more then one link.

But am stuck on how to do full mesh bgp, how do i go about it, like R3 - R4, and R4-R5 and R5 - R6 or how do i go about it.

LVL 14

Expert Comment

ID: 40393846
Full-mesh would require that each router is configured as a neighbor to every other router.  So, in your diagram, on R1, you'll configure a neighbor to R2, R3, R4, ... , R9.  Same then for R2 (neighbors to R1, R3, ... , R9), and so on.  This can become tiresome on 30 routers, which is where route-reflectors start to become handy.

Remember that BGP runs on TCP sessions between BGP speakers, so a) neighbors does not need to be directly connected, and b) you will still need an IGP for internal reachability.

Author Comment

ID: 40394160
Thank you for the response.

To make it simple, can i make R1 and R2 to be route reflectors and R3 to R7 to peer with R1 and R2 ? Would that work ? and do i do iBGP ? and if a client connects to R5 and R9, how can i do BGP with client, Ibgp or eBGP ?  thanks.

I have ospf for internal reachability.
LVL 14

Accepted Solution

Otto_N earned 400 total points
ID: 40394350
Yes, you can make R1 and R2 route reflectors, but why don't you want to add R8 and R9 as route-reflector clients?  If you do not add R8 & R9 as route reflector clients, you have to set-up a full mesh between R1, R2, R8 and R9.

You can also have multiple RR clusters: For example use R1 as RR for R3 & R4, R7 as RR for R9, and R2/R6 as RRs for R1, R5, R7 & R8.  This can get tricky, though - A router can only be RR for a single cluster, but can be a RR client in another cluster.  Also, if a RR is not a client in another cluster, it must be fully meshed to other BGP speakers that is not RR clients.  Best practice would indicate that you set down clear design rules for which routers are/can be route reflectors, if multiple route-reflector clusters will be allowed, and design rules regarding these.  The simpler these rules, the less chance there will be of mistakes creeping in.

Route-reflectors are specific for iBGP (devices within the same AS), and I assumed R1 - R9 will run on the same BGP AS number.  If a client connects to you, best practice dictates eBGP (to connect a client via iBGP will require inclusion in your OSPF process, and being configured either as a route-reflector client, or full mesh to RR's and other non-clients - not reccommended!)

Author Closing Comment

ID: 40398605
Thank you for the detailed explanation, this will help me plan my network. I am going set a design on paper and then implement it.

Thanks again.

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