Re: LL32 Multihoming

At 11:02 AM 6/25/2003, Erik Guttman wrote:
>Stuart,
>
>This issue reawakens concerns raised by Erik Nordmark which we have
>already dealt with in the 'issue resolution process.'
>
>Stuart Cheshire wrote:
> > 2(b). Therefore: It is helpful to ensure that no local interface has
> > an IPv4 address that it identical to *any* peer connected via *any*
> > interface.
>
>We had language like this in the document which was removed because
>it gives rise to a new and significant vulnerability. (See LL14)
>A host on one link can disrupt hosts on other links (it is not
>connected to) if IPv4LL has this property.
>
>Example: Imagine a multihomed host H1 is connected to links 1 and 2.
>An attacker is on link 1 and causes H1 to reconfigure by claiming
>addresses.  This should only effect link 1, not link 2.  The effects
>could be wider than the links immediately connected to the attacker's
>multihomed neighbors.  Following the example:  Host H2 is connected to
>both link 2 and link 3.  As H1 is forced to reconfigure its address on
>link 2 to be unique, this forces H2 to reconfigure as well, which has
>consequences on link 3.
>
>LL14 was rejected since LL15 was accepted:  the algorithm being
>completely separate on each interface meant that the vulnerability no
>longer arises.  Your 2b above conflicts with the accepted LL15 and if
>ignored gives rise to the concern in LL14 - which can no longer be ignored 
>(rejected.)

Umm, this doesn't follow well from the first message in this discussion thread.

Stuart talked about a concern regarding IP address collision with one's own 
interfaces. Since a host CAN validate the source MAC address of the packets 
that come back it's possible to determine if you're arguing iwth yourself. 
It's still true someone could spoof your MAC address in an ARP packet to 
cause damage, but as we know that's a place where ARP has issues, and we 
can't solve them here.

Erik, you're talking about reconfiguration based on claims (possibly bogus) 
of use of IP address. Aside from someone spoofing the MAC address as well, 
it isn't clear your response aligns with the problem Stuart raised.

I think what Stuart is talking about both has merit, and relates to 
operational experience, and deserves to be considered as such. Laptops with 
multiple interfaces are now the norm (for all new products shipping, since 
the push to put 802.11a/b/g/x/y/z is near universal).

Dan