Subject: Unsolicitated Neighbor Advertisement on Link-Up

From: Walter Zimmer <[email-masked]>
Date: Thu, 24 Oct 2002 18:11:09 +0200

Hi!

When unplugging an IPv6 node from an ethernet switchport and
plugging it back into another, the host is not reachable until
the switching table timeout expired (or any ARP timeout occurs).

Therefore, in this respect, IPv6 is not superior to IPv4.

Are there any negative consequences if an IPv6 node sends out
an unsolicitated neighbor advertisement after the link comes up
again? It might choose a random delay (e.g. up to 1 sec), but
I think this would be beneficial in hiding the ugly details of
switching tables from the user.

Or did I miss it and it is already included in some IPv6 spec?
I looked into NDP (RFC 2461) and IPv6 over Ethernet (RFC 2464).

Thanks for any info on this topic,
Walter
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From: Greg Daley <[email-masked]>
Date: Fri, 25 Oct 2002 15:33:41 +1000

Hi Walter,

There's some related discussion going on with
the optimistic DAD draft, which proposes this
idea as part of the optimization for DAD.

Just sending a NA when no-one has data for you
may not have any effect though.

Greg Daley

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From: Walter Zimmer <[email-masked]>
Date: Fri, 25 Oct 2002 10:22:18 +0200

Hi Greg!

> idea as part of the optimization for DAD.
Thanks for the pointer to this interesting (yet lengthy :)
discussion.

I still see differences between the operation proposed
in the O-DAD draft and the mechanism used here:

In the draft, a router advertisement with a different
prefix is the trigger for the UNA, whereas here it is
the link state transition to 'up'. If an IPv6 router
sends a NA on link up (it doesn't ?), there still is no
change of routing prefix involved here.

Therefore, I think this application should be restricted
to the ethernet link layer.

> may not have any effect though.
The host might remember if there was traffic going on
before the link went to 'down' state. Yet, I would assume
that the benefit of saving NAs doesn't outweight the
cost involved.

Walter