IPv6 support for com/net zones on October 19, 2004

Thu Oct 28 12:02:01 UTC 2004

On Thu, Oct 28, 2004 at 01:45:28PM +0200, Niels Bakker wrote:
> Anyone else care to comment?  The hop count is suspiciously lower for
> IPv6 than for IPv4, and has twice the latency (coming from Europe too).
> But again, this is traceroute `wisdom'.

One problem with IPv6 traceroute is, that Cisco got two things
severly wrong in some versions:

- TTL might not decremented when switching packets into GRE tunnels
- ICMP TTL exceeded must be sourced from ingress interface. IOS
  violated that in some versions and used the EGRESS interface IP
  as source for the ICMP packets.

Both bugs do severely hurt traceroutes and interpretation of them
as you cannot be sure wether you are actually experiencing them or
not. Unfortunately those IOS versions are still seen in the wild,
and because the v6 world still uses (far too many senseless) tunnels.
So interpreting traceroutes in v6 can sometimes really be considered
guesswork, even more than in v4. :-Z

Best regards,
Daniel

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