/128 IPv6 prefixs in the wild?

Justin M. Streiner streiner at cluebyfour.org
Thu Dec 15 14:15:36 UTC 2011

On Thu, 15 Dec 2011, Glen Kent wrote:

> In the service provider networks, would we usually see a large number
> of /128 prefixs in the v6 FIB tables?

If you have /128s on the loopbacks of your routers, your other routers 
could learn the /128s for the loopbacks of your other routers 
through your IGP.

> What are the scenarios when IPv6 routers would learn a large number of
> /128 prefixes?

Two questions:
1. What is a 'large number' in this case?
2. Are the addresses from your v6 range(s), or something else that 
wouldn't be coming from the outside world (link-local, etc)?

> I would presume that most IPv6 prefixes that the routers have to
> install are less than /64, since the latter 64 is the host part. Is
> this correct?

Looking at the routing table on one of my lab routers, I only see the /64 
for a remote network in its v6 routing table, along with the interface and 
link-local address of the router it wants to use to reach that 
destination.  I do not see any separate entries for any smaller chunks of 
that /64.


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