Re: [RRG] incrementally deployable

[Christian Vogt <christian.vogt@nomadiclab.com>]

David -

> I haven't read deep enough into all of the proposals to figure out 
> which ones are incrementally deployable. 

Amongst those solution proposals that use IP address mappings [Shim6,
Six/One, LISP, eFIT, Ivip], incremental deployability is equivalent to
the use of globally routable IP addresses on both sides of the mapping.

If IP addresses are globally routable, packets can reach their
destination with and without a mapping.  Hosts can then communicate even
if the mapping is not supported on either one's side.  All it takes is a
mechanism that discovers lack of mapping support on the remote side and, 
in such a case, disable the mapping on the local side.

Six/One and Shim6 are incrementally deployable because they use
provider-dependent IP addresses, which are aggregatable and hence can be 
represented in the global routing table in a scalable manner.  Ivip, 
too, is incrementally deployable because it uses provider-dependent IP 
addresses in combination with globally routable anycast IP addresses.

For techniques that use non-routable IP addresses on the host side of
the mapping, such as LISP, reachability of hosts depends on a mapping
being accomplished on both sides of a packet flow.  This precludes
incremental deployment because for one edge network to deploy the
technique without loss of global reachability, all other edge networks
must deploy the technique also.

- Christian




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