[AG-TECH] multicast config (Nortel) ?

Charles R. Anderson cra at WPI.EDU
Fri Feb 7 10:57:57 CST 2003

On Thu, Feb 06, 2003 at 10:41:14PM -0800, Andrew Daviel wrote:
advax>  ** include this line in reply to prevent spamtrapping **
advax> I'm having some trouble configuring multicast routing and
advax> wondered if anyone had any experience with Nortel equipment
advax> (or just general advice).
advax> We have a Nortel Passport 8600  (8603 ?) router and BayStack 450 switches.
advax> We are connected to CA*net and hence Internet2 via BCnet.
advax> See Fig 1 (attached).
advax> We have a static RP set on the passport using an address supplied by 
advax> BCnet.

First, a few general things:

1. IGMP snooping can be a pain.  It is much better to make your IGMP
snooping domains as small as possible (i.e. subnet your network).  I
understand that this may not be possible in your situation...

2. You should configure static router querier ports on your 450's for
both IGMP v1 and IGMP v2 on the ports towards your router.
Additionally, the 450's have a feature called IGMP Proxy.  Try turning
this off.

3. Upgrade your 450 code to the latest.  IGMP is one of those things
that seems to break in various ways from release to release.  Older
releases had a particularly nasty bug where IGMP Proxy would proxy
requests coming in on a port back out the same port using the client's
Ethernet address as the source of the proxy report! This would disrupt
all communications to every multicast-capable host on your entire

4. I recommend using PIM-SM throughout.  Don't use DVMRP.  In your case,
since you only have one router, you are already using PIM-SM
"everywhere".  PIM-SM should be enabled on your LAN VLAN interface and
the CA*Net interface.

advax> Currently, if I fire up SDR, stations A & B can see announcements from the
advax> Internet, but C and D cannot. (D is my desktop so it's really annoying...)  
advax> If I send simple multicast packets from A,B,C or D then the other stations
advax> can see them (this is a tiny ping-like thing I hacked together from a CS
advax> course assignment somewhere). If I create sessions in SDR on one of the
advax> stations then the others can see them, usually. D will see C immediately,
advax> A will see B immediately, and there may be a delay for A to see C or D.

You should start your troubleshooting at the receiver, while the source
is known to be active. Is the receiver sending IGMP reports for the
specific group you are interested in receiving? Are they reaching the
router? Obviously some reports are reaching the router or you wouldn't
receving any traffic to A or B, so this sounds like a possible IGMP
snooping problem.  Check the 450 "Multicast Group Membership" screen to
be sure all the proper ports for interested receivers are listed.

You should check the Passport, which should be the PIM DR for your
subnet. Make sure it is the DR, and no other router on the network has
taken that role:

show ip pim interface

Look for the router's own IP address for your LAN VLAN; if you see a
different IP address in the DR column, then some other router is trying
to be the DR.

Then check to be sure the Passport's PIM state lists all the
proper ports in the Outgoing Ports where the interested receivers are
for the specific group you are trying to receive:

show ip pim mroute grp

advax> We recently tried a test to a site on CA*net from B using static 
advax> ip addresses e.g. "vic". We could see them but they could 
advax> not see us. It occurred to me later that I may not have started vic with
advax> a big enough TTL; I think I had set the threshold in the Passport to 15.

Note that the Passport with non-E blades won't pass packets with a TTL of 1.

If they cannot see you, that is a different problem entirely.  They
would have to start troubleshooting from their end, tracing the IP
Multicast state all the way back to you.  The most you could do is look
for PIM state on your router:

show ip pim mroute grp w.x.y.z

and check the Incoming Port to be sure it matches the port where your
VIC source is, and the Outgoing Ports to see if the CA*Net port shows up

advax> Ideally I would like multicast to work anywhere on site, and we would like 
advax> to restrict the multicast data e.g. AG video from going down branches 
advax> where it is not required, which I think is what IGMP snooping will do for 
advax> us. So I'd like to understand what it is about port 4 and port 6 that 
advax> means one works and one doesn't (I can't see any config differences).
advax> And of course I would like to be able to send offsite.

Your best bet would be to seriously consider subnetting your network.
IGMP snooping is a hack at best, and relying on it for your entire Class B
is a bad idea.

advax> Anyone know a good introduction to multicast networking, preferably 
advax> free & online - though a good book would work too ?

The book "Interdomain Multicast Routing" by Edwards is excellent. The
examples are for Cisco and Juniper routers, but I'm not aware of any
Nortel/Passport-specific multicast books, unfortunately.

Charles R. Anderson			cra at wpi.edu
Network Engineer			(508) 831-6110
Computing and Communications Center	(508) 831-6666
Worcester Polytechnic Institute	    Fax (508) 831-5483

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