8.2. Border/Edge Tunnel Routers

8.2. Border/Edge Tunnel Routers

Using Customer Edge (CE) routers for tunnel endpoints allows the EID space associated with a site to be reachable via a small set of RLOCs assigned to the CE routers for that site. This is the default behavior envisioned in the rest of this specification.

This offers the opposite benefit of the first-hop/last-hop Tunnel Router scenario: the number of mapping entries and network management touch points is reduced, allowing better scaling.

One disadvantage is that fewer network resources are used to reach host endpoints, thereby centralizing the point-of-failure domain and creating network choke points at the CE router.

Note that more than one CE router at a site can be configured with the same IP address. In this case, an RLOC is an anycast address. This allows resilience between the CE routers. That is, if a CE router fails, traffic is automatically routed to the other routers using the same anycast address. However, this comes with the disadvantage where the site cannot control the entrance point when the anycast route is advertised out from all border routers. Another disadvantage of using anycast Locators is the limited advertisement scope of /32 (or /128 for IPv6) routes.