Re: [shim6] Problems with ULID (IP) over longer sessions.

[Erik Nordmark <[e-mail]>]

On 04/28/10 05:20 AM, Javier Ubillos wrote:
> Hi folks.
>
> Some time ago I heard a discussion about a potential issue with shim6.
> That the Upper Layer Identifier (ULID), chosen as the first pair of
> locators used in the communication, could cause
> problems/confusion/somethingelse when those locators where no longer
> used by the hosts. I.e not in the locator lists.
>
> I'm unsure about the details of what would cause the problem or what the
> consequences could be.
>
> My own first reaction is that if a software believes it's communicating
> with an IP (a shim6 ULID), it might try to spawn more sockets/flows to
> that IP.
>
> Have this kind of issues been discussed previously on this list? ( I
> couldn't find any discussions about it).
> Have any one on this list some more detailed thoughts/experience about
> what could cause issues?

Section 1.5 in RFC 5533 says that the communication must be terminated 
should the ULID become invalid. That handles the case of a ULID 
potentially being assigned to a different host.

Note that a ULID might be unreachable and hence unusable as a locator 
without being invalid.

> I'm asking this because a couple of colleges and I are looking at using
> alternative ULIDs which hopefully would be more of a match with session
> identifiers/FQDNs or similar.

It is possible to extend SHIM6 to handle 128-bit ULIDs that are never 
usable as locators. It has performance impact because one would need to 
do a ID->locator lookup before sending the first packet. A possible way 
to do this was written up in draft-nordmark-shim6-esd.

    Erik