User Manual

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81.1.5 BGP/MPLS VPN Route Advertisement
In basic BGP/MPLS VPN networks, VPN route advertisement concerns CE and PE, since P routers only
maintains routes of the backbone network, and doesn’t need any VPN route information. PE routers only
maintain the VPN route information directly connected to it, not all VPN routes. SO the BGP/MPLS VPN
network is easy to extend.
The VPN route advertisement process includes three parts to create a reachable route from the local CE to
the remote CE, enabling the advertisement of VPN private network route information in the backbone network:
from local CE to ingress PE, from the ingress PE to the egress PE, from egress PE to the remote CE.
The followings are introduction to the three parts:
The route information switch from the local CE to the ingress PE
CE will send the local VPN route to the PE directly connected to it after establishing an adjacency to the latter.
CE can use static routes, RIP, OSPF, IS-IS or EBGP to send routes to PE, all in the form of standard IPv4
routes.
The route information switch from the ingress PE to the egress PE
PE will add RD and VPN target attributes to the VPN routes it learns from CE, then store these VPN-IPv4
routes into the VPN instances created for CE.
The ingress PE will advertise the VPN-IPv4 routes to the egress PE via MP-BGP. The egress PE will
determine whether to add this route into the route table of VPN instance according to the routes’ Export Target
attribute and the import Target of the VPN instances it maintains.
Different PEs ensure the intercommunication between them via IGP.
The route information switch between the egress PE to the remote CE
Like the route information switch from the local CE to the ingress PE, there are many available methods for
the remote CE to learn VPN routes the egress PE, including static route, RIP, OSPF, IS-IS and EBGP.
81.1.6 Multi-AS VPN Introduction
In real networking applications, multiple sites of a user VPN may connect to SP with different ASN, or to
different AS of the same SP. Such applications of one VPN crossing multiple autonomy systems are called
Multi-AS VPN. RFC 2547 provides three Multi-AS VPN resolutions:
 VRF-to-VRF：ASBR use VRF interface to create EBGP neighbors and manage VPN routes, which is
also called Inter-Provider Option A;
 EBGP Redistribution of labeled VPN-IPv4 routes： ASBR use MP-EBGP to advertise label
VPN-IPv4 routes, which is also called Inter-Provider Option B;
 Multihop EBGP redistribution of labeled VPN-IPv4 routes：PE use Multi-hop MP-EBGP to advertise
label VPN-IPv4 routes, which is also called Inter-Provider Option C.
At present we support the first resolution: VRF-to-VRF Multi-VPN resolution.
Multi-VPN resolution
As demonstrated in the nest figure, in this mode, PE routers from two AS directly connects with each other,
and serve as ASBR of the AS they belong to. These PE routers (ASBR) connect with each other via VRF
interfaces, import all RT this system need the other end to learn, export all RT this system want to obtain from