Subject: Multicast Traceroute and multicasting responses to response address

From: Mladen Sablic <[email-masked]>
Date: Wed, 19 Jul 2000 19:07:11 +0100

Hi all,

I have a question on multicast traceroute implementation.

I am confused on how to implement response sourcing when the response address
is multicast. In the draft: -
http://www.ietf.org/internet-drafts/draft-ietf-idmr-traceroute-ipm-06.txt
s.6.5.3 & s.6.5.4. it says that I should find a source address that is known to
the mulitcast routing table but if I am the router I am not likely to have
any (S,G) enteries with me as a source. Which interface I should send it out
towards the source of the query or the receiver as don't know where the client
is located?

Do I pick a random multicast enabled interface, join the group on it and send?

For example in PIM-SM, if a trace reaches the RP and there is no (S,G) route
towards the source so the trace has finished. RP's address is not known to the
multicast routing table, the client can be located at the source,
destination or other managment location and the response address is set
to 224.0.1.32 (mtrace.mcast.net).

Where does the RP send the response?

Mladen

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From: Bill Fenner <[email-masked]>
Date: Mon, 24 Jul 2000 14:27:42 -0700

>I am confused on how to implement response sourcing
>when the response address is multicast. In the draft: -
>s.6.5.3 & s.6.5.4. it says that I should find a source address that is
>known to the mulitcast routing table but if I am the router I am not
>likely to have any (S,G) enteries with me as a source.

Thanks for pointing this out.  What it *means* is an address known in
the topology database used by multicast (e.g. an address that belongs to a
prefix that's routed in MBGP).  The intent is to maximize the possibility
that the response is routable.

>Do I pick a random multicast enabled interface, join the group on it

You don't need to join the group.  If you can't pick an interface that's
routed (either because you don't have one or because you don't know
what's routed), picking a random interface is reasonable.

  Bill