Route information in can be transmitted BGP was only IPv4 unicast, but in MP-BGP (MultiProtocol-BGP) , the address of the various protocols other than IPv4 unicast has been enhanced so that it can be transmitted.
MP-BGP, rather than make the BGP and different protocols, has been achieved by increasing the BGP of the Path Attribute.For this reason it is backward compatible.
In RFC2283 new Path Attribute Type 14 and Type 15 have been defined.
Multiprotocol Reachable NLRI (type14)
Path Attribute Type 14
Format: [Address Family Information, Next Hop Information, NLRI]
Multiprotocol Unreachable NLRI (type 15)
Path Attribute Type 15
Format: [Address Family Information, Unfeasible Routes Length, Withdrawn Routes]
The Address-family, by RFC2453 and RFC2858 was defined by the IANA, is the association of the protocol and the AFI.
Address Family Information is Cool composed [AFI, SAFI (Sub-AFI )].
AFI and stands for Address Family Identifier, is the information that identifies the address of the transmission protocol.
AFI = 1 ⇒ IPv4
AFI = 2 ⇒ IPv6
The SAFI (Sub-AFI), is the detailed identification of the identified protocol in the AFI.
Sub-AFI = 1 (SAFI = 1) ⇒ Unicast
Sub-AFI = 2 (SAFI = 2) ⇒ Multicast
Sub-AFI = 4 (SAFI = 4) ⇒ NLRI with MPLS Labels
Sub-AFI = 128 (SAFI = 128) ⇒ MPLS-labeled VPN address
In addition, further Path Attribute Type 16 in RFC4360 has been defined.
Extended Communities (type 16)
Path Attribute Type 16
Format: [Type high, Type low, Value]
In the case of Route-Target, it will be the Type high = Ox00, Type low = Ox02.
As usage of other Extended Communities, you can send the information such as the domain ID when redistributing OSPF to MP-BGP.If the domain ID matches the OSPF process of facing router, you can put together a super backbone.More about this later .
Overview of MPLS-VPN will be described the flow of the MP-BGP in the configuration shown in, it will be as follows.
PE1 and PE2 is usually set the BGP peers in the same AS, but exceptionally NextHop will be its own source IP.
Next Hop is 0: 0: 220.127.116.11 0: 0 is equipped with a RD that although this is a specification of the MP-BGP, because of the constraint that the "format of NextHop must be aligned with those shown in the AFI" is.
The above details, please refer to the RFC3107, RFC4364.