Re: Transport multihoming

[Feico Dillema <feico@pasta.cs.uit.no>]

On Fri, Oct 25, 2002 at 07:14:32AM +1100, Peter Tattam wrote:
> On Thu, 24 Oct 2002, Iljitsch van Beijnum wrote:
> 
> > Greg, Peter,
> > 
> > As I see it, the reason to have the multihoming functionality inside one
> > or more transport protocols is that the transport layer has end-to-end
> > knowledge that makes it possible to make better multihoming decisions.
> 
> My recent thoughts are that it need not be tied directly to the TCP protocol,
> but can instead be done at the IP layer of the host stack.  However the TCP and
> IP layers should be aware of each other in much the same way that PMTU is
> facilitated.  If done that way, there would be benefits from caching the
> multihoming information and sharing it over several connections.  Also because
> of the strong aggregation, the cached information would be able to build a
> multihoming hint tree more efficiently than would a flat list of IP addresses. 
> For example, if a major link from one aggregator showed a problem, it would
> take provide a hint that all aggregations from that provider would be
> inaccessible and the stack could use this intelligence in advance. 
Instead of letting hosts negotiate the prefixes why not
augment/generalize PMTU into a ``Path Capability (or MTU and Prefix) Discovery''
(or do something traceroute-like) that collects the information from
all nodes along the path. This might allow for some nice
aggregation and double-checking of information (assuming routers are
typically more trustworthy or better maintainedi than most hosts).

Feico.