Subject: Being DIS on more than 256 LANs

From: Radia Perlman - Boston Center for Networking <[email-masked]>
Date: Fri, 23 Jul 1999 09:27:11 -0400 (EDT)

I believe the current proposal says that you cannot be DIS on
more than 256 LANs, and I don't think that's a necessary
restriction. I argued privately with a couple of people at the IS-IS
working group meeting and convinced them.

I believe that all you need is a unique (in the
area) 7 byte ID for the LAN, and
that the DIS has to pick that 7 byte unique ID. Maybe some weird
dependency got added later, but as I designed IS-IS,
there was no reason why the bottom 6 bytes of the ID had to match the
system ID of the DR...it just was a convenient method of getting
a unique 7 byte number. So therefore, if the router knows some more
EUI-48's (which it almost certainly will, one for each LAN interface),
then it can form unique 7-byte quantities by taking one of those
EUI48's for the next 256 LANs on which it's DR, etc.

So for example, you have R1, R2, R3, and R4 on a LAN. R1 gets elected DR.
But it's already DR on 255 other LANs. So it has another EUI-48, let's
call that "R9". So it names this LAN R9.1. All the routers (including R1)
announce an adjacency to R9.1. R1 (on behalf of the LAN) announces
it is R9.1 and has neighbors R1, R2, R3, R4.

And in fact, if there were some bizarre reason why R1 was connected
to a zillion LANs without having more than one EUI-48, it could
use other values of the G/I and G/L bits in the OUI, to give it 4 different
unique 6-byte numbers to use in forming 7-byte LAN names. Again, the LAN
name should just need to be a unique 7 byte number. It shouldn't
bother anyone if the bottom 6 bytes looks like an Ethernet multicast
address, or looks locally assigned, or doesn't match the system ID of
any of the routers on that LAN.

I briefly browsed through the IS-IS document again to see if anything
got added since the DECnet Phase V design that might require an adjacency
between Rx.k and Rx, but I don't see any, and can't imagine why that would
be needed.

Radia

---

From: Rajesh Saluja <[email-masked]>
Date: Fri, 23 Jul 1999 11:11:55 -0400

Are you proposing that a router can have multiple system ids?
and the router will make adjacency with neighbors on different
interfaces using different system ids? Does not it mean that you
need to originate multiple  non-pseudonode LSPs
corresponding to each  system id and you need to advertise the
appropriate LSP to each interface.

Thanks,
Rajesh

--

-------------------------------------------------------------
Rajesh Saluja
Nortel Networks Inc 600 Technology Park Billerica, MA  01821
Ph: (978) 288-7791      Fax: (978) 670-8760
--------------------------------------------------------------

---

From: Tony Li <[email-masked]>
Date: Fri, 23 Jul 1999 10:52:21 -0700

> Are you proposing that a router can have multiple system ids?

Not exactly.  It would effectively have other unique numbers that it
would fill in pseudonode LSP id's with.  It would still retain a single
identity and issue a single non-pseudonode LSP.

> interfaces using different system ids?

Yup.

> Does not it mean that you

There's no need to originate multiple non-pseudonode LSPs.  There's
simply an advertised adjacency between the non-pseudonode LSP for the
system and a variety of pseudonodes using the other LSP ids.  There's no
change to the flooding algorithm.

Tony