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MP-BGP address family

mpbgp small122You may be familiar very well with BGP protocol but probably until you don’t start use MPLS L3 VPN or IPv6 you will not have awareness that the other kind of BGP addresses exist. For carrying the other BGP addresses responsible is Multi Protocol BGP,  that we  break down right now.

Usually when we think about BGP we think about routing protocol that is responsible for exchanging ipv4 routes  between Autonomic Systems, what is true, but nowadays extension of BGP that is called MP-BGP  can do much more. It doesn’t mean if router is capable to carry ipv4 BGP will be able to carry the other address families, some routers have  implemented MP-BGP some don’t have. The type of traffic that MP-BGP carrys is called address-family. One of the thing that has to be done in order to establish the neighborhood  is that you  have to point out the type of traffic. OK, but you didn’t have to do that  so far. Let’s have a look  on 2 lines of configuration :

router bgp 1
neighbor remote-as 1

what you will may find in running-config if you configured the other address-family before ?:

router bgp 1
neighbor remote-as 1
address-family ipv4 unicast
neighbor activate

It turns out, BGP does everything for us, because ipv4 unicast address family is default type. We also have to point out under address-family the neighbor and activate its. We don’t have to  activate any address, if we use default ipv4 unicast until we input command no bgp default ipv4This command causes that for each neighbor we have to define address family. If we want to leave given address family we have to use “exit-address-family“, within the single BGP instance we may  use a couple of address families.

The types of BGP address-family

First of all, BGP uses NLRI The Network Layer Reachability Information what is nothing more than network and prefix for example and during the BGP session between 2 peers describes the type of information that they will be exchanging.

We destinguish Address family identifier that is responsible for sending information regarding the network layer protocol AFI and Subsequent address family identifiers – SAFI, that is additional information about type of used NLRI

Some of address families :

ipv4 unicast – default address family

l2vpn – if we are going to deploy VPLS (L2VPN MPLS)

vpnv4 – L3 VPN (MPLS) the BGP peers share exported prefixes from directly connected VRFs . Each prefix has assigned Route Distinguisher.

ipv4 vrf NAME – we create a routing instance for specific VRF forwarding.Firstly we define neighbor under  vpnv4, then we create VRF instances and at the end we create a routing instance for this VRF within BGP

RTFILTER unicast – in case we want to reduce unnecessary traffic, if we use its two MPBGP peers will not exchange routes from all VRFs that are connected to.


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