Subject: Re: draft-ietf-zeroconf-ipv4-linklocal-03.txt

From: Thomas Narten <[email-masked]>
Date: Wed, 11 Jul 2001 09:28:23 -0400

Daniel Senie <[email-masked]> writes:

> >    If the destination address is:
> >    (a) a unicast address outside the 169.254/16 prefix, or
> >    (b) a multicast address with scope larger than link-local and
> >        the TTL in the IP header is greater than 1,
> >    then the host MUST NOT use its link-local source address, and should
> >    instead use an appropriate routable source address.
> >
> >why?

> link local addresses should not be used behind NAT devices, since there's 
> no mechanism to distribute a "default gateway" other than ICMP Router 
> Discovery, and the discussion on a proposal in this whole general area was 
> strongly opposed to using link local addresses with NAT gateways.

> Keeping link local to a truly local state avoids a variety of interesting 
> and odd cases.

> The limit on the TTL also ensures people don't try to route link-local, 
> which has some interesting (and likely bad) side effects (address conflict 
> resolutions, etc.).

IMO, having routers not forward link-local packets and doing the
TTL=255 trick provides adequate protection to the forwarding problem.

I think I've responded to your other comments in other postings.

> >I'd suggest in the name of network friendliness that after ten tries,
> >one should either quit entirely (maybe too extreme) or at least back
> >off *very* significantly, say no more than once every few minutes or
> >so.

> Quitting is a bad idea. It would mean that one disturbance on a network 
> could permanently shut down devices. Backing off is reasonable, though.

Right. I think you want to backoff enough so that the traffic
contributed doesn't become an issue (once a second seems too high). I
agree also that if you quit, then you run into the situation where a
temporary hiccup in the network doesn't get corrected on its own
(i.e., nodes would need to be restarted after the network was back in
proper working order). That's not something we want either.

Thomas