Date: Tue, 6 Nov 2001 12:41:29 +0200 (EET)
From: Pekka Savola <[EMAIL PROTECTED]>
Message-ID: <[EMAIL PROTECTED]>
| Consider a scenario:
|
| Router B plugged in the network with Router A (e.g. cross-over cable).
| Neither has anything configured or set up yet on this link.
| 3ffe:ffff::1/127 address is added to Router A; now it DAD's for
| 3ffe:ffff::1 (normal address) and, being a router in the subnet, also
| 3ffe:ffff::0, and succeeds.
My point was that it must not. That is, if there are to be two nodes
on a link, and there are two addresses available, it is positively insane
for one of the two nodes to take both of them.
If it wants (either via some config file, or just random chance) to pick
the xxx0 address, then it gets to be the target of the anycast. If it
doesn't, then it doesn't...
It can't pick the xxx1 address for itself, and then go ahead and also
pick the xxx0 address to be anycast. If an I-D needs to be written to
make this (self-evident) truth clear, then I guess we should write one.
I know that the normal use of anycast is for everyone eligible to assign
themselves the address, but there's nothing in the definition that requires
that - this just happens to be a scenario where that is inappropriate
behaviour.
| Now, there are interesting variations of this in cases of router reloads,
| crashes etc. when this subnet-router anycast address becomes "free to
| get".
If you mean that things can flap around in such cases when using auto-config
(not based upon stable identifiers), then yes, of course. That's pretty
much self-evident too.
| The fact remains, as shown in the scenario above, that on router-router
| links, using /127 is impossible unless subnet-router anycast addresses are
| restricted or disabled.
No, go back to my first message - it isn't impossible at all. It just
needs rational considered implementations.
If anything, what we have now when systems use /127 for p2p links is
the use of the subnet-router anycast address ready made (even though
most probably the nodes don't know that's what they're doing, and in the
rare cases when one end is a host rather than a router, the host might
have the subnet-router address inappropriately). Everything is working
just like it should.
kre
--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page: http://playground.sun.com/ipng
FTP archive: ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [EMAIL PROTECTED]
--------------------------------------------------------------------
