Vpn-Ipv4 Address - Avaya 8600 Technical Manual

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VPN-IPv4 Address

Please note that the RD is simply a number that you configure. It does not identify the origin of the route
nor does it specify the set of VPNs to which the routes are distributed. Its sole purpose is to simply
provide a mechanism to support distinct routes to a common IPv4 address prefix. By allowing different
RDs to support the same IPv4 addresses, over-lapping addresses can be supported. Please note that
the RD does not specify the VRF(s), it is simply provides a means to identify a PE node which may
contain one or more VRF's.
For each Virtual Router and Forwarding (VRF) instance, it will be associated with one or more Route
Target (RT) attributes. In summary, a route target simply identifies a particular VRF. When IPv4 traffic
from a CE router is forwarded to a PE router that in turn is required to be forwarded to another PE router,
a VPN-IPv4 route is created. The VPN-IPv4 route will contain a route target extended community that is
advertised or exported by the PE router export policy. Any PE router in the network that matches the
route target via its route target import policy will import the route for that particular VRF. In BGP, layer 3
IPVPNS route targets control VRF route propagation between PE routers. Please note that there is only
one route distinguisher but there are be multiple route targets. The route target frame format is identical to
the route distinguisher as shown above.
If one or more of the PE routers all belong to the same Autonomous System, the PE router can distribute
VPN-IPv4 routes to each other by means of an iBGP connection between them. If scaling is an issue
because there are too many PE router to peer with, BGP route reflectors can be used. When a PE router
distributes a VPN-IPv4 route via BGP, is uses its own address as the BGP next hop address. In regards
to the ERS8600, a circuitless IP address (CLIP) is used to peer between PE routers and is also used as
the MPLS router-id and OSPF router-id if OSPF is configured as the IGP.
The VPN-IPv4 routes are distributed by MPLS labels. The MPLS label switched paths are used as the
tunneling mechanism. Hence, all nodes in the network must support Label Distribution Protocol (LDP)
and in particular Downstream Unsolicited mode must be supported for Ethernet interfaces. If LDP is not
used, then some other form of tunneling is required, ie. GRE. LDP uses implicit routing, thus it relies on
the underlying IGP protocol to determine the path between the various nodes in the network. Hence, LDP
uses the same path as that selected by the IGP protocol used. The ERS8600 uses LDP for VPN-IPv4.
VPN Packet Forwarding
IV-VPN (MPLS) for ERS 8600 Technical Configuration Guide
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