Unique RD per PE in MPLS VPN for Load Sharing and Faster Convergence
This post describes how load sharing and faster convergence in MPLS VPNs is possible by using an unique RD per VRF per PE. It assumes you are already familiar with MPLS but here is a quick recap.
The Route Distinguisher (RD) is used in MPLS VPNs to create unique routes. With IPv4, an IP address is 32 bits long but several customers may and probably will use the same networks. If CustomerA uses 10.0.0.0/24 and CustomerX also uses 10.0.0.0/24, we must in some way make this route unique to transport it over MPBGP. The RD does exactly this by prepending a 64 bit value and together with the IPv4 address, creating a 96-bit VPNv4 prefix. This is all the RD does, it has nothing to do with the VPN in itself. It is common to create RD consisting of AS_number:VPN_identifier so that a VPN has the same RD on all PEs where it exists.
The Route Target (RT) is what defines the VPN, which routes are imported to the VPN and the topology of the VPN. These are extended communities that are tagged on to the BGP Update and transported over MPBGP.
MPLS uses Continue reading

