8.1. First-Hop/Last-Hop Tunnel Routers

8.1. First-Hop/Last-Hop Tunnel Routers

By locating Tunnel Routers close to hosts, the EID-Prefix set is at the granularity of an IP subnet. So, at the expense of more EID-Prefix-to-RLOC sets for the site, the caches in each Tunnel Router can remain relatively small. But caches always depend on the number of non-aggregated EID destination flows active through these Tunnel Routers.

With more Tunnel Routers doing encapsulation, the increase in control traffic grows as well: since the EID granularity is greater, more Map-Requests and Map-Replies are traveling between more routers.

The advantage of placing the caches and databases at these stub routers is that the products deployed in this part of the network have better price-memory ratios than their core router counterparts. Memory is typically less expensive in these devices, and fewer routes are stored (only IGP routes). These devices tend to have excess capacity, both for forwarding and routing states.

LISP functionality can also be deployed in edge switches. These devices generally have layer-2 ports facing hosts and layer-3 ports facing the Internet. Spare capacity is also often available in these devices.