From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Wed Aug 18 2004 - 19:48:34 GMT-3
John,
Anytime to send traffic with a multicast destination, you are
generating a "feed". The router can generate this with features such as
ping, traceroute, or SAA. The reason the S,G entry shows up in R2's
routing table is because it received a "feed" from 150.1.1.1 going to
the group 255.5.5.5. If R1 receives an ICMP echo-reply from R2, then
the end to end path is good. If R1 doesn't receive the reply, the
majority of the time it is due to RPF failure.
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> John Matus
> Sent: Wednesday, August 18, 2004 3:51 PM
> To: lab
> Subject: multicast basic question
>
> ok, here goes...
> in a lab scenario, one where there is no real multicast feed to play
> with....
> say the lab asks you to configure pim on routers 1, 2 and 3 and also
asks
> that
> routers 1, 2, and 3 join multicast group 225.5.5.5. and then asks
that
> router
> 1 be able to get ping responses from 2 and 3....
>
> when you join an interface to a multicast group ( ip igmp join-group
> 225.5.5.5), i've noticed that it will show up in the other router's
mroute
> tables as (150.1.1.1, 255.5.5.5) (from r2's perspective). my
question
> is
> does that somehow create a 'source' of multicast traffic since it
shows up
> in
> the mroute table? some of the labs i've seen will ask you to
configure
> multicast and then tell you that you can use static mroutes, but i
don't
> see
> how it is possible to test for RPF is there is no real multicast
source.
> so
> i'm confused about 1) what a multicast source is in these lab
scenarios
> and 2)
> how do you test for RPF without a 'source'
>
> also, if i join routers 1, 2, and 3 to multicast group 225.5.5.5,
should
> they
> all respond to pings to that group....and if they don't, am i supposed
to
> use
> static mroutes to get to each other? (this is all just hypothetical of
> course)
>
> thanks in advance!
>
>
>
> John D. Matus
> MCSE, CCNP
> Office: 818-782-2061
> Cell: 818-430-8372
> jmatus@pacbell.net
>
>
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