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(ASCEND) Virtual IP routing / IP Navigator

Just read some stuff on "IP Navigator"'s Virtual IP Routing capabilities.
(http://www.ascend.com/2871.html).

The Virtual IP routing (splitting the router into multiple independant
logical routers) sounds like a very cool, but also very unconventional
feature.

This functionality certainly has a lot of repercussions for the
router's architecture. I'm curious as to how some of these are dealt
with. Does anyone have any experience with this?

I guess this is implemented by assigning each interface on the router
(perhaps an ISDN connection, an Ethernet interface, or a Frame/ATM
PVC) to exactly one of the multiple different routing groups.

How is route caching implemented? Of course the route cache is only
valid for one of the virtual routers. Having multiple route caches
probably isn't feasible because the route cache may be in SRAM which
is limited in quantity, or the route cache (especially in the case
of the GRF) may be held right on the interface card which has a
fixed, relatively small amount of RAM. Hypotheses:

  - Route cache is only used for the 'main' router. Not a real good
    solution, all the other virtual routers take a big performance hit.
  - Route cache is tagged with an extra key which identifies the
    virtual router to which the cache entry belongs and keeps the
    virtual routers separate
  - The number of possible virtual routers is seriously limited by
    available cache RAM.

My guess is the second one?

Another point is routing processes, like OSPF. Incidentally, is the
implementation of OSPF in IP navigator better than the Max 4k
implementation seems to be from comments on the list? (I have not
yet tried Max 4K OSPF myself out of fear!).

Sounds like a big undertaking to implement all the routing protocols
in such a way that multiple independent copies thereof can be run on
the same router, one for each virtual router. Has Ascend really
pulled this off nicely?

-Phil
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