RE: ip6-localhost (::1) 2990.86 ms !H -> Why ?

From: Pekka Savola (pekkas@netcore.fi)
Date: Sun Nov 18 2001 - 06:27:37 EST


On Sun, 18 Nov 2001, NDSoftware wrote:
> > Capture traffic with 'tcpdump -i interface -n ip6' on both
> > ends and see
> > that the messages (ICMP neighbour solications, when you ping6
> > the other
> > end's link-local address) get through.
>
> On router:
>
> 12:15:39.109604 0:d0:70:1:81:1b 33:33:ff:0:0:1 86dd 86:
> 6000 0000 0020 3aff 3ffe 8271 2101 0001
> 0000 0000 0000 0001 ff02 0000 0000 0000
> 0000 0001 ff00 0001 8700 d1ab 0000 0000
> 3ffe 8271 1000

I suggest you upgrade tcpdump to at least 3.6.2, to get IPv6
enabled. It's difficult to say whether these are the same packets.

> On Woody:
>
> 21:38:02.882404 3ffe:8271:1000:22::1 > ff02::1:0:1: icmp6: neighbor sol:
> who has 3ffe:8271:2101:1::1
> 21:38:03.882226 3ffe:8271:1000:22::1 > ff02::1:0:1: icmp6: neighbor sol:
> who has 3ffe:8271:2101:1::1

As said, use link-local addresses.

> > Another explanation for this is that IPv6 neighbour discovery code is
> > messed up. This can happen if you take down your loopback
> > interface.
>
> ifdown lo and after:

I'm not sure what you mean by this. In Red Hat Linux terms:

Works:

 - ifdown lo ; ifup lo

Doesn't fix the problem:

 - ifconfig lo down ; ifconfig lo up
   (plus possibly readded routes)
 
 ==> you would have to re-add addresses like ::1/128 on the interface too
     (even though they already exist there)

> traceroute to 6bone.net (3ffe:b00:c18:1::10) from 3ffe:8271:2101:1::1,
> 30 hops max, 16 byte packets
> 1 * * *
> 2 * * *
> 3 * *
>
> traceroute to 3ffe:8271:1000:22::1 (3ffe:8271:1000:22::1) from
> 3ffe:8271:2101:1::1, 30 hops max, 16 byte packets
> 1 * * *
> 2 *

Using global addresses depend on a lot of other configuration being right
too. Use only link-local when debugging until that works properly.

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords

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