Internet Edge Router replacement - IPv6 route table sizeconsiderations

George Bonser gbonser at
Thu Mar 10 12:52:37 CST 2011

> If you configure a /64, you are much more likely to have guaranteed
> forwarding speed to that destination, and guaranteed number of routes
> in FIB.  What you don't have is a guarantee that ARP/NDP will work
> correctly on the access router.  If you choose to configure a /120,
> you may lose one or both of the first guarantees.  The
> currently-available compromise is to configure a /120 on the access
> device and summarize to a /64 (or shorter) towards your
> aggregation/core.  I see nothing wrong with this, since I allocate a
> /64 even if I only configure a /120 within it, and this is one of the
> driving reasons behind that decision (the other being a possible
> future solution to NDP table exhaustion, if one becomes practical.)

What I have done on point to points and small subnets between routers is
to simply make static neighbor entries.  That eliminates any neighbor
table exhaustion causing the desired neighbors to become unreachable.  I
also do the same with neighbors at public peering points.  Yes, that
comes at the cost of having to reconfigure the entry if a MAC address
changes, but that doesn't happen often.

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