[radvd-devel-l] DeprecatePrefix option

Pekka Savola pekkas at netcore.fi
Wed Mar 9 16:08:32 EST 2011

On Wed, 9 Mar 2011, Mark Smith wrote:
>              Upon shutdown, this option will cause radvd to deprecate
>              the prefix by announcing it in the radvd  shutdown  RA
>              with  a  zero preferred lifetime and a valid lifetime
>              slightly greater than 2 hours. This will encourage
>              end-nodes using this prefix to deprecate any associated
>              addresses immediately. Note that  this option  should
>              only be used when only one router is announcing the
>              prefix onto the link, otherwise end- nodes will deprecate
>              associated addresses despite the prefix still being valid
>              for preferred use.

Have you tested this on two routers, how does a host really behave 
when it gets zero preferred lifetime and a 2h valid lifetime -- and 
subsequently, from another router, a higher lifetime?

I'd assume that the other router keeps advertising the longer 
lifetime, and the hosts will continue to keep using the prefix, and 
will also initiate new connections immediately after hearing back from 
the other router.

One reason for longer default lifetimes in v6 was that if a router 
goes down for some time, internal connectivity using the addresses 
still keeps working. This could be still be useful in limited scale, 
e.g., enough time for the system to reboot, for example (10min). But 
in practise, the lifetimes have decreased and this is probably no 
longer a useful goal, given the drawbacks.

If this works reasonably out of the box, I wonder if the default 
should be to enable this feature.

Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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