Comment on draft-coene-sctp-multihome-04.txt

[Brian E Carpenter <brc@zurich.ibm.com>]

Lode,

You state that:

>     Under the assumption that every IP address will have a different,
>     seperate path towards the remote endpoint, (this is the
>     responsibility of the routing protocols or of manual configuration)
>     , if the transport to one of the IP addresses (= 1 particular path)
>     fails then the traffic can migrate to the other remaining IP address
>     (= other paths) within the SCTP association.

Now in the original context that SCTP was designed for, you might have that 
much control over the routing environment. But it seems to be a very dangerous
assumption for the general case of two systems communicating over the
whole Internet.

I actually think this points to an important component of any solution
that we haven't really talked about much, except when NAROS was discussed
a few months ago - how does one determine the existence or absence of
connectivity between two locators? For SCTP or any other solution,
it's only when connectivity exists between an address pair that they
are any use.

By the way, you also say

> 
>     As a practical matter, it is recommended that IP addresses in a
>     multihomed endpoint be assigned IP endpoints from different TLA's to
>     ensure against network failure.

The term "TLA" no longer exists in IPv6 and in any case, it is a false
assumption that two different high-order network prefixes imply
two different paths. They might, but they might not.

  Brian