8. Deployment Scenarios
8. Deployment Scenarios
This section will explore how and where ITRs and ETRs can be deployed and will discuss the pros and cons of each deployment scenario. For a more detailed deployment recommendation, refer to [LISP-DEPLOY].
There are two basic deployment tradeoffs to consider: centralized versus distributed caches; and flat, Recursive, or Re-encapsulating Tunneling. When deciding on centralized versus distributed caching, the following issues should be considered:
o Are the Tunnel Routers spread out so that the caches are spread across all the memories of each router? A centralized cache is when an ITR keeps a cache for all the EIDs it is encapsulating to. The packet takes a direct path to the destination Locator. A distributed cache is when an ITR needs help from other re-encapsulating routers because it does not store all the cache entries for the EIDs it is encapsulating to. So, the packet takes a path through re-encapsulating routers that have a different set of cache entries.
o Should management "touch points" be minimized by only choosing a few Tunnel Routers, just enough for redundancy?
o In general, using more ITRs doesn't increase management load, since caches are built and stored dynamically. On the other hand, using more ETRs does require more management, since EID-Prefix-to- RLOC mappings need to be explicitly configured.
When deciding on flat, Recursive, or Re-encapsulating Tunneling, the following issues should be considered:
o Flat tunneling implements a single tunnel between the source site and destination site. This generally offers better paths between sources and destinations with a single tunnel path.
o Recursive Tunneling is when tunneled traffic is again further encapsulated in another tunnel, either to implement VPNs or to perform Traffic Engineering. When doing VPN-based tunneling, the site has some control, since the site is prepending a new tunnel header. In the case of TE-based tunneling, the site may have
control if it is prepending a new tunnel header, but if the site's ISP is doing the TE, then the site has no control. Recursive Tunneling generally will result in suboptimal paths but with the benefit of steering traffic to parts of the network that have more resources available.
o The technique of re-encapsulation ensures that packets only require one tunnel header. So, if a packet needs to be re-routed, it is first decapsulated by the ETR and then re-encapsulated with a new tunnel header using a new RLOC.
The next sub-sections will examine where Tunnel Routers can reside in the network.