Subject: Multicast Traffic.

From: [email-masked]
Date: Wed, 18 Mar 1998 11:47:47 -0500

Hello all, I am currently playing around with Netshow channels, encoding AV
at bitrates between 50kbps and 100kbs.  I am trying to determine if this
traffic will have any affects on other segments of the network.   For
instance if I set the TTL=1 on my broadcasts, how will this affect the
routers on other segments of the network.  If they are not configured for
multicasting, am I correct in saying that only the router attached to my
segment will experience load?  Or will this traffic be routed out to other
segments?  Say the router is mcast enabled, then it definitely will not
route the traffic to other segments.  Correct?

Thanks
Phil

---

From: "John M. Zwiebel" <[email-masked]>
Date: Wed, 18 Mar 1998 09:53:35 -0800

^ 
 ^ 
 ^ 
 ^ 
 ^ Hello all, I am currently playing around with Netshow channels, encoding AV
 ^ at bitrates between 50kbps and 100kbs.  I am trying to determine if this
 ^ traffic will have any affects on other segments of the network.   For
 ^ instance if I set the TTL=1 on my broadcasts, how will this affect the
 ^ routers on other segments of the network.  If they are not configured for
 ^ multicasting, am I correct in saying that only the router attached to my
 ^ segment will experience load?  Or will this traffic be routed out to other
 ^ segments?  Say the router is mcast enabled, then it definitely will not
 ^ route the traffic to other segments.  Correct?
 ^ 
 ^ 
Packets with a ttl of 1 will not be forwarded.  

------------------------------------------------------------------------------
	John Zwiebel                       Phone: 408-526-5303
	Cisco Systems Inc.                 
	Multimedia Group

---

From: [email-masked] (Jeremy Hall)
Date: Wed, 18 Mar 1998 13:05:28 -0500 (EST)

Each routing device that forwards the packets will decrement the ttl by 1,
so the first router will set it to 0 and drop the packet.

You should be able to set the ttl to 15 and (hopefully) your packets won't
escape into the mbone.  The unicast routers will ignore the multicast
packets.

If you have a cisco router for your mbone connection, make sure the line

ip multicast ttl-threshold 32

or something similar appears on the interface going towards the mbone.  If
a packet arrives at the router, and the ttl in the packet is less than 32,
it will not be sent down the external link because the threshold prevents
it.

_J