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List:       ms-ospf
Subject:    Re: OSPF Multicat Messages
From:       "Moy, John" <John.Moy () SYCAMORENET ! COM>
Date:       1999-08-19 20:14:55
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The OSPF multicast addresses AllSPFRouters and AllDRouters are
link-local multicast addresses. The semantics of these addresses require
that you specify the interface when sending. For example, in the BSD
socket interface you would use the IP_MULTICAST_IF setsockopt()
to specify what interface the packet is to be sent out of.

John

-----Original Message-----
From: Senthil K. Venkatachalam
[mailto:senthil.venkatachalam@ADN.ALCATEL.COM]
Sent: Wednesday, August 18, 1999 8:06 PM
To: OSPF@DISCUSS.MICROSOFT.COM
Subject: OSPF Multicat Messages


Hi all,

I have a question on the multicasting OSPF
messages (to addresses such as ALL_SPF_ROUTERS).

Lets say I have 2 interfaces, one pt-to-pt interface (Ia), and
one broadcast ethernet interface (Ib) (on which it is DR).
Say I have established adjacencies with neighbors R1 and R2,
R1 on the ethernet and R2 at the other end of the pt-to-pt link.

If I need to send an LSU to R2 in response to an LSR, then I'd send
a multicast OSPF message to AllSPFRouters, intended for R2.

My question is, will this message then also be sent on the ethernet
interface to router R1? I think it will, because the IP layer has no way of
knowing which interface to send on, since both of them accept this
particular multicast address. Is this correct?

Thanks,
Senthil.
--

Senthil K. Venkatachalam     senthil.venkatachalam@adn.alcatel.com

Off: 2L08, MBox: 2145A       (703) 724-2635 [Off]

Alcatel USA                  (703) 724-2003 [Fax]

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