RE: Question for IPv6 w.g. on [Re: IPv6 Type 0 Routing Headerissues]

Two scenarios that are much less harmful are 
when there is only 1 address in only one RH0:
1) when the intermediate destination address and the final
destination address are addresses of the same node.
2) when the final destination address is equal to the 
source address.

In both cases, the intermediate destination isn't being
used as transit between two other nodes.  A sample use
case of the second scenario is for a round-trip 
traceroute.

-Dave

-----Original Message-----
From: Jari Arkko [mailto:jari.arkko@piuha.net] 
Sent: Friday, April 27, 2007 10:44 AM
To: bob.hinden@nokia.com
Cc: Brian Carpenter; IETF IPv6 Mailing List
Subject: Re: Question for IPv6 w.g. on [Re: IPv6 Type 0 Routing
Headerissues]

>  1) Deprecate all usage of RH0
>  2) Recommend that RH0 support be off by default in hosts and routers
>  3) Recommend that RH0 support be off by default in hosts
>  4) Limit it's usage to one RH0 per IPv6 packet and limit the number
> of addresses in one RH0.

My preference is 2 or alternatively 1. I am currently not
aware of any real use case for Type 0 header (but please
educate me if there is some). It has been known to be
dangerous for a long time and without a use case, it
seems waste of energy to work on 4 or other more
detailed limitations to make it safe. In particular
I would very much like to see us publishing the
RFC deprecating/turning this off soon. Developing the
rules for 4 is possible, but it will take time.

More fundamentally, I believe functions like this
need to be tailored to a specific need before they
can be made restricted enough to be safe and
useful at the same. This is what was done with
Type 2, for instance. If we will see a future need
for something like this, I suspect that it may need
a new Type number anyway.

Alternative 3 is an interesting one. It would actually
align IPv6 with current IPv4 specifications. RFC 1812
calls for a configuration option to turn off source routes,
but requires the default to be that the source routes
are processed. I'm not sure this is right, however...
perhaps we should update corresponding IPv4
specifications at the same time, too.

Jari

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