From: Chris Lewis (chrlewiscsco@gmail.com)
Date: Tue May 16 2006 - 17:21:35 ART
Tony,
There is never a packet sourced from a multicast address, as such you only
need to specify the group address and hence atandard access lists are
perfectly adequate for identifying one address.
For the second issue, the IGMP membership will be sent to teh group address,
a debug on a router that has a host joining 227.7.7.7 would show the
following
*Mar 1 03:19:54.983: IP: s=12.12.12.1 (FastEthernet0/0), d=227.7.7.7, len
28, rcvd 0, proto=2
Chris
On 5/16/06, Tony Paterra <apaterra@gmail.com> wrote:
>
> Hey all, another multicast question... I'm trying to control what
> multicast groups users can join on a specific interface (for instance
> everyone an Router A's Ethernet interface can't join Administratively
> scoped groups). The examples I've seen of doing this involve the
> following...
>
> RouterA(config-if)#ip igmp access-group 1
> RouterA(config)#access-list 1 deny 239.0.0.0 0.255.255.255
> RouterA(config)#access-list 1 permit any
>
> My question is targetted at understanding if this operates the same
> for potential IGMP v1 receivers as well as IGMP v2 . That is to
> say... If I have a v1 PC on that LAN that sends an IGMP Membership
> Report (v1) is the router smart enough to dig inside of the v1 packet
> to get the group address and say "no you can't join 239.x.x.x" even
> though the packets will be destined for 224.0.0.1.
>
> Also if you could explain why a standard access list works in this
> case. Logic tells me that this should only work on IGMP traffic
> sourced from 239.x.x.x, but that wouldn't be the case for IGMP
> Membership Reports (they would be sourced from whatever the host IP
> is), they would be destined for that address so my logic seems to be
> fundamentally wrong...
>
> Thanks,
> --
> Tony Paterra
> apaterra@gmail.com
>
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