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BGP Route reflector

What is BGP Route reflector and how can it help advertise local routes to internet? Does it work with CE ??
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Hi,

When your using IBGP you need to have each IBGP peer fully meshed because of BGP split horizon.

This doesn't scale very well when you have many IBGP peers, so you can use a route-reflector to minimise the number of IBGP peers. Another alternative is to use confederations which break down your AS into sub-AS's.

Author

Commented:
So, with confederation, a large number of prefixes ready for advertisement to internet can be brought down, I am surely interested in this scheme... please shed some more light on it.

Thanks;

Commented:
No, both Route-reflectors and Confederations are used to reduce the number of IBGP peers each router needs to maintain (which grows exponentially when increasing the number of peers).  The number of prefixes advertised will remain exactly the same.

To reduce the number of prefixes, you'll use summarisation.
Marius GunnerudSenior Systems Engineer
Top Expert 2013

Commented:
Because IBGP will not advertise any other IBGP learned route you need to use a route reflector.  Lets say we have RouterA, RouterB and RouterC.  RouterA learns a route through EBGP and advertises it to RouterB.  RouterB has now learned this new route through IBGP and assumes that since it is learned through IBGP that all other routers already know of this router and therefore will not advertise this new route to Router C.  To tell RouterB to advertise the newly learned IBGP route you will need to configure route reflector on RouterB for both RouterA and RouterC.  this is so that both routers can know how to reach eachother.

A confederation devides an AS into many AS. To the outside world the network looks to be one AS but internally they look to be many AS.  There might still be need to use route reflector within the confederations depending on how many routers and how they connect to eachother.

Author

Commented:
Is there any tool you know of which can be used to compact the prefix'es , some type of automatic route summarization...
Commented:
No, not that I know of, and I think it is a good thing.  Route summarization should be once-off, and based on proper IP address planning and network design, for which there are many tools and online resources available to make it easier.  But the design is still user-specific:  How many IP's do you want to reserve for where?  And no tool will tell you that.

A dynamic system (that adapt to prefixes being received) will defeat the purpose, as changes will cause new route updates anyway, propagating instability while using up more computing resources.

Author

Commented:
Well, take a simple case where two contigous /24 prefixes are being advertised...compaction will make it 1 prefix of /23. Something that goes thro the prefix'es and figures a better way to rearrange..
Marius GunnerudSenior Systems Engineer
Top Expert 2013
Commented:
How did we get to summarization from route reflector? lol...anyway.

Well, in BGP it is not called summarization but route aggregation.  Consider the following network:

RouterA--------RouterC--------RouterB
                          |
                          |
                          |
                      RouterD

RouterA advertises 10.10.10.0/24, RouterB advertises 10.10.11.0/24. So, lets say that the summarized address is 10.10.0.0/16.  On RouterC to aggregate the two advertised addresses and then advertise that aggragated address to RouterD you need to issue the following commands:

enable
config t
router bgp 10 (or whichever process number you are using)
aggregate-address 10.10.0.0 255.255.0.0 summary-only

Author

Commented:
Thanks;

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