CCDE – Inter AS L3 VPNs
Introduction
Sometimes a customer needs a L3 VPN between two locations where the same SP is not present. This can be on a national or international basis. It would be possible to buy an Internet circuit and run an overlay such as DMVPN but what if the customer wants to buy a MPLS VPN circuit?
The customer could buy a VPN from SP1 in location1 and a VPN from SP2 in location2. The two SPs would then have to exchange traffic somehow to make the customer circuit end to end. The concept is shown in the following topology.
The customer connects to the PE of each of the SPs. The SPs need to interconnect at some common point, either through a public peering place such as an IX or with an private interconnect at a common location. The routers that connect to each other are called autonomous system border routers (ASBR). There are three main options and a fourth option which combines two of the others.
Inter-AS Option A
Option A is the most simple of the options to interconnect the ASBRs. Each customer VRF requires either a physical interface or more likely a subinterface. Option A has Continue reading