Understanding VPN-IPv4 Addresses

Because each VPN has its own private address space, the same IP address might be used in several VPNs. To provide for more than one route to a given IPv4 address (each route unique to a single VPN), BGP/MPLS VPNs use route distinguishers (RDs) followed by an IPv4 address to create unique VPN-IPv4 addresses. A route can have only one RD.

The RD contains no routing information; it simply enables you to create unique VPN-IPv4 address prefixes. You can specify the RD in either of the following ways:

You can create unique VPN-IPv4 addresses by assigning a unique RD to each VRF in your network. However, the optimal strategy depends on the configuration of your network. For example, if each VRF always belongs to only one VPN, you might use a single RD for all VRFs that belong to a particular VPN.

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