Re: administrivia (on avoiding injury)

[Daniel Senie <dts@senie.com>]

Margaret Wasserman wrote:
> 
> >
> >How do you accomplish getting an unmodifyed station to change the source
> >address it uses?
> 
> IPv6 doesn't have statically defined addresses like IPv4 does.
> Hosts receive their address prefixes on a temporary basis through
> IPv6 Host Autoconfiguration or a stateful configuration mechanism
> (DHCP).  All IPv6 stacks support autoconfiguration.

How quickly these addresses will get updated in DNS, making it possible
to serve out services in this model remains to be seen.

> 
> So, it would be possible (although I am still working to determine
> whether it would be practical) to change the IPv6 routers to deprecate
> prefixes for which connectivity has been lost.  IPv6 hosts will
> choose (for any new connection) a non-deprecated address over a
> deprecated one.

Well, if there are multiple hosts on a local net who are using those
addresses for communications among themselves, I have some real concerns
about sending them messages to cease such communications. The routers
may not be a party to all conversations, after all.

> 
> It is fairly easy to understand how new IPv6 routers could get
> current IPv6 hosts to start using a new address to establish new
> connections.
> 
> The hard part is figuring out how the new IPv6 router knows that
> the host should start using a new address at all.  In other words,
> how do routers within the site determine that Internet connectivity
> through a particular ISP has been lost?

How do we do it today? It's hard. We often DON'T know that connectivity
is lost. We're often not talking about carrier detect dropping on a
link. I think THIS is one of the underlying issues in need of a solution
if any sort of host-based multihoming is to be considered. The knowledge
of link outage would have to be propagated QUICKLY to hosts, meaning
we'd have to be able to detect that outage in a very timely fashion.
Another thing needed is a definition of LINK OUTAGE. I propose a link is
declared dead when it's not carrying traffic as intended. This may
translate to a policy that states packet loss over 90% on a link leads
to an assumption of death, rather than a traditional "T1 link is down,
therefore reroute" type of decision.



-- 
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Daniel Senie                                        dts@senie.com
Amaranth Networks Inc.                    http://www.amaranth.com