HP 6125XLG R2306-HP 6125XLG Blade Switch MCE Configuration Guide - Page 5

After a CE establishes an adjacency with a directly connected PE, it advertises its VPN routes to the PE and learns remote VPN routes from the PE. A CE and a PE can use BGP, an IGP, or static routing to exchange routing information. After a PE learns VPN routing information from a CE, it uses BGP to advertise the VPN routing information to other PEs. A PE maintains routing information for only directly connected VPNs, rather than all VPNs on the provider network. A P router maintains only routes to PEs and does not deal with VPN routing information. When VPN traffic travels over the MPLS backbone, the ingress PE functions as the ingress Label Switching Router (LSR), the egress PE functions as the egress LSR, and P routers function as the transit LSRs. MPLS L3VPN concepts Site A site has the following features: • A site is a group of IP systems with IP connectivity that does not rely on any service provider network. • The classification of a site depends on the topology relationship of the devices, rather than the geographical positions, though the devices at a site are, in most cases, adjacent to each other geographically. • The devices at a site can belong to multiple VPNs, which means a site can belong to multiple VPNs. • A site is connected to a provider network through one or more CEs. A site can contain many CEs, but a CE can belong to only one site. Sites connected to the same provider network can be classified into different sets by policies. Only the sites in the same set can access each other through the provider network. Such a set is called a VPN. Address space overlapping Each VPN independently manages its address space. The address spaces of VPNs may overlap. For example, if both VPN 1 and VPN 2 use the addresses on subnet 10.110.10.0/24, address space overlapping occurs. VPN instance In MPLS VPN, routes of different VPNs are identified by VPN instance. A PE creates and maintains a separate VPN instance for each directly connected site. Each VPN instance contains the VPN membership and routing rules of the corresponding site. If a user at a site belongs to multiple VPNs at the same time, the VPN instance of the site contains information about all the VPNs. For independence and security of VPN data, each VPN instance on a PE maintains a routing table and a label forwarding information base (LFIB). VPN instance information contains the following items: the LFIB, IP routing table, interfaces bound to the VPN instance, and administration information for the VPN instance. The administration information for the VPN instance includes the route distinguisher (RD), route filtering policy, and member interface list. RD MPLS L3VPN adds an RD field before an IPv4 address to change the IPv4 address to a VPN-IPv4 address. PEs use MP-BGP to advertise VPN routes with VPN-IPv4 addresses. A VPN-IPv4 address consists of 12 bytes. The first eight bytes represent the RD, followed by a four-byte IPv4 address prefix. 2