Re: [RRG] incrementally deployable

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

Darrel:

> What if a 3rd party provides a proxy between the two systems, then 
> incremental deployment is possible. Then networks who are not LISP 
> capable can reach EIDs that are not in the global Routing table.

This proxy would defeat the purpose of any multi-homing solution in
terms of reducing an edge network's dependency on a provider, since the
edge network would then depend on the provider operating the proxy.  The
edge network would probably also have to pay for the proxying service.

Two more issues with this proxy approach depend on the type of
addressing space proxies would advertise in BGP:

(a) If proxies advertised EID space, the number of global routing table
    entries could not be reduced.

(b) If proxies advertised LOC space, hosts in upgraded networks would
    continue to be reached via LOC addresses, and this reduces the
    benefit of the EID/LOC split.

Ivip avoids the dependency on a single proxy by grouping multiple
providers to do the proxying for redundancy.  An edge network's EID
space is then advertised by multiple providers.  To reduce the number of
routing table entries, Ivip also groups edge networks, and it uses one
EID block per edge network group.

The Ivip model creates new dependencies, though:

- Providers in a group are bound to other providers in the group.  They
  must coordinate their BGP advertisements because a customer edge
  network of one provider is also a customer of the other providers in
  the group.

- Edge networks in a group are bound to other edge networks in the group
  because they cannot leave the group without renumbering.

- Edge networks are bound to their provider group because they cannot
  move to a provider in a different group without renumbering.

> Alternatively, what if an xTR performs NAT between PA space and EID 
> space?

This is classic NAT'ing.  It's no longer LISP because the IP address
mapping won't be reversed.  Furthermore, NAT'ing reduces the benefit of
the EID/LOC split because hosts continue to be reached via LOCs.

- Christian




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