From: Brant Stevens (branto@xxxxxxxxxxxxx)
Date: Sun Oct 21 2001 - 13:41:08 GMT-3
224.0.0.x is a reserved address group...
----- Original Message -----
From: "Brian Hescock" <bhescock@cisco.com>
To: <ccielab@groupstudy.com>
Sent: Sunday, October 21, 2001 11:18 AM
Subject: multicast tip
> The previous discussion about multicast made me think about a problem I
> see occasionally and I thought I'd pass it along. Don't use anything in
> the 224.0.0.x range for a multicast address. It will work fine if the
> source and destination are in the same vlan (unless you're using one of
> the reserved addresses, such as 224.0.0.10 for eigrp, which would
> probably wouldn't be a good thing to do... ;-). The reason it doesn't
> work when routing multicast is the 224.0.0.x is a "link-local" address,
> it never gets forwarded off the local segment, you will never get ip
> multicast for 224.0.0.x to work across a router unless you bridged it
> (haven't tried it but it should work).
>
> Most people wouldn't use 224.0.0.x but I see it happen occasionally and
> wanted to help save some people the grief of troubleshooting the problem
> if you used that range of addresses by mistake. Another common problem
> in production networks is many multicast servers have a default ttl of 1
> and, since one of the first things a router does is decrement the ttl by
> one, the packets get dropped at the router. The solution is to increase
> the ttl of the multicast server to be at least one higher than the
> number of hops to the furtherest multicast receiver.
>
> Brian
>
> p.s. in case anyone was wondering, the previous e-mail with my comment
> about mutlicast being on by default was referencing a discussion about
> NLSP, not ip multicast (the part about NLSP was further down in the
> e-mail thread).
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