[c-nsp] IPv6 duplicate address

[Gert Doering]

Hi,

On Tue, May 27, 2008 at 03:00:26AM +0300, Hank Nussbacher wrote:
> When we did some line testing and did some loop testing on the link we got:
> %IPV6-4-DUPLICATE: Duplicate address FE80::215:2CFF:FE87:B240 on POS11/0/0
> 
> petach-tikva-gp# sho ipv6 int pos11/0/0
> POS11/0/0 is up, line protocol is up
>    IPv6 is stalled, link-local address is FE80::215:2CFF:FE87:B240 [DUP]
[..]

> I know I can use "ipv6 nd dad attempts 5" but wanted to know whether I 
> should open a TAC case for this.

I have seen this as well, and it's especially annoying if it happens
as consequence of a link outage from the carrier (link going down, going
into "loop" state, then coming back to "up") - if you're unlucky, a short
glitch can kill your IPv6 on the line hard until you manually reset the
interface.

The current behaviour is pretty much a direct consequence from the RFC
(DAD is mandatory), but I think that IOS could be a bit more smart about
it, like "restart DAD every 5 minutes" or "recognize a looped->up 
transition on the interface, and then restart DAD".

So - by all means, please open a TAC case.

As a workaround, we have used "ipv6 nd dad attempts 5" on the specific
line that gave us headaches - so we've never pressed the issue with Cisco.

gert


-- 
USENET is *not* the non-clickable part of WWW!
                                                           //www.muc.de/~gert/
Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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