From: Brian Hescock (bhescock@xxxxxxxxx)
Date: Sun Oct 21 2001 - 13:48:58 GMT-3
People seem to use it anyway... ;-) And for every one we see I'm sure
there are 10 times that out there where people do the same thing but
then try another address (that isn't reserved) and it works. It was
just a fyi so people don't make the simple mistake we see.
B.
Brant Stevens wrote:
>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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