BGP tabel per VFR or singel BGP tabel

[kumara.saman]

Hi,

As per my knowledge when we create a VRF and bind OSPF process to it.

there is a separate OSPF table per VRF. Is this true for BGP also or there is only one Global BGP tabel for all VRFs and we use RD to differentiate routes from several VRFs. 

[Rolf Fischer]

Hi,

this is a really huge topic which fills whole books.

To give you a basic idea: Segregation of routing-tables with different VRFs (separate ipv4 address-families) can also be done with BGP. But at the same time, Multiprotocol BGP creates so called VPNv4 prefixes by prepending all the VRF-IPv4 prefixes with the appropriate RD (address-family vpnv4) in order to create unique routing information (address ranges of different customers/VRFs could overlap). This VPNv4 prefixes then can be advertised to neighboring peers and those peers can assign the IPv4 prefixes again to their approriate VRF by evaluating the RDs. Thus you do not need to peer for every single (VRF) IPv4 address-family.

So you can have various per-VRF BGP tables on one router but only one "global" VPNv4 table. The per-VRF instances consist of the customer's routing information and the VPNv4 table is exchanged among PEs of the service provider network.

HTH

Rolf

[Giuseppe Larosa]

Hello Rolf,

the decision to import a VPNv4 prefix into a locally defined VRF is based on route target(s) of the VPNv4 prefix not on the RD. The route target(s) are BGP extended community attributes of the VPNv4 prefix.The local PE node compares the route target(s) with those configured in the locally defined VRF site, if there is a match the route is installed in the VRF routing table as a BGP route. To be noted unless using complex configurations, it is enough that one of the route targets associated to the VPNv4 prefix matches one of the imported route target(s) in the VRF to have a valid match,

Hope to help

Giuseppe

[Rolf Fischer]

Hello Giuseppe,

thanks for the correction. When I wrote this, I was first thinking about mentioning route targets as well but then I didn't want to over-complicate the answer because the original question seemed to me somewhat generic. After re-reading I have to admit that my attempt to simplify has led to an inaccurate description.

Thanks again,

Rolf

[nagak]

I agree with Giuseppe. Good reply thanks.