Re: Transport level multihoming

[Peter Tattam <peter@jazz-1.trumpet.com.au>]

On Thu, 9 Aug 2001, Greg Maxwell wrote:

> On Thu, 9 Aug 2001, Peter Tattam wrote:
> 
> > One question.
> >
> > In a transport level multihoming scenario, should two addresses that differ in
> > the lower 64 bits (node address part) be considered independent nodes and
> > handled in the traditional manner with regard to multiple addresses?
> 
> My opinion is that:
> 
> Hosts should consult DNS to get a list of addresses associated with a name
> and pass these addresses to the transport API. This set of addresses MAY
> or MAY NOT be for a single host.
> 
> The transport protocol will then attempt to connect, most likely by trying
> to tack up a connection with the first host on the list. The transport
> level will communicate the rest of the valid addresses for the hosts.
> 
> This allows DNS to continue to round robin separate hosts, as well as
> initiating link.
> 
> > Why I ask is that the upper 64 bits of all possible full addresses for a
> > particular node that is multihomed have particular properties that would be
> > useful to exploit in transport level multihoming.  If the lower 64 bits is not
> > identical between multiple addresses, it could lead to inefficiencies in a
> > compressed representation of the list of IPv6 addresses.  It may also be
> > important to some layers of any multihoming protocol to consider that addresses
> > which differ in the lower 64 bits would not being equivalent for the purposes
> > of multihoming.
> 
> I don't believe using the lower 64 bits to identify the host is the
> correct solution. For example, what happens when I want to use the
> 16bits of site networking to perform future-internet-like multihoming
> inside my own AS (I probably wouldn't do this because of address
> proliferation and because I wouldn't have scaling problems with
> traditional multihoming on a local scale)?
> 
> Or a more obvious example: The 8+8 limits the minimum network that can
> separately multihome to /64. On the IPv4 internet, people complain that
> some providers filter their deaggregated /24 announcements!
> 
> I would have to see some pretty compelling optimizations for a change
> which would effectively exclude all small institutions from multihoming.
> 
> 
> 

I am not precluding this.  Perhaps I should expand the argument to relax the
restriction on the 64 bit boundary and say that if a site is multihomed with N
upper bits, can we consider that if the lower 128-N bits are the same, they can
be considered the same node address.  Anything else is another address.

Peter

--
Peter R. Tattam                            peter@trumpet.com
Managing Director,    Trumpet Software International Pty Ltd
Hobart, Australia,  Ph. +61-3-6245-0220,  Fax +61-3-62450210