From: Geert Nijs (geert.nijs@simac.be)
Date: Thu Aug 24 2006 - 20:20:45 ART
Rick,
I should look up the details, but maybe IGMP snooping works only on IGMP
Membership reports.
If there is no router querying (sending IGMP Query messages), then maybe there
are also no IGMP Membership reports......so snooping will block all
multicast.....
If you enable snooping (without the special configuration), do you see the
multicast MAC address being registered on the receivers ports ???
I guess not...
That is why you must configure the switch itself as the IGMP querier, since
their is no router in the vlan generating the IGMP Query messages.....
Just a thought.....
regards,
Geert
-----Oorspronkelijk bericht-----
Van: Rick Fox [mailto:rick.fox@tcsna.com]
Verzonden: donderdag 24 augustus 2006 15:53
Aan: Geert Nijs; Brian McGahan; ccielab@groupstudy.com
Onderwerp: RE: ICMP snooping on non-routed VLAN
Thanks Geert. The vlan is only on one switch. The article is very good,
however did not provide a valid solution for a sup720. The only idea that I
can come up with is creating a vlan interface with an IP address, and using
the
igmp snooping querier
interface command. This is not really how I wanted to do this, but seems to
be the only solution without changing the code. The document shows this
command as a global configuration command, but it is only available on the
interface on a sup720.
Thanks,
Rick
________________________________
From: Geert Nijs [mailto:geert.nijs@simac.be]
Sent: Thu 8/24/2006 6:35 AM
To: Rick Fox; Brian McGahan; Rick Fox; ccielab@groupstudy.com
Subject: RE: ICMP snooping on non-routed VLAN
Rick,
Is there only one switch involved ?
If multiple switches are involved connected through L2 links, then IGMP
snooping can indeed be a problem, even in one VLAN.
This is because an IGMP snooping enabled switch will "snoop" and actually
"capture" an IGMP Membership report.
It will ONLY forward this request on ports it thinks are IGMP router ports.
If the switch thinks it does not have any router ports, it will not forward
the IGMP Membership report at all and this can generate problems......
More information can be found here: (very nice article, or why multicast can
be a pain in the a$$ even in one VLAN :-)
http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note0918
6a008059a9df.shtml#understand
regards,
Geert
CCIE #13729
________________________________
From: nobody@groupstudy.com on behalf of rick.fox@tcsny.com
Sent: Thu 8/24/2006 0:46
To: Brian McGahan; Rick Fox; ccielab@groupstudy.com
Subject: Re: ICMP snooping on non-routed VLAN
I have a vlan configured on a sup720 without a l3 interface, with servers and
receivers sharing that vlan. The hosts do not receive any multicast traffic
until I turn off IGMP snooping. I thought it could be a bug, but figured I
was forgetting something. Any ideas?
Thanks.
-----Original Message-----
From: "Brian McGahan" <bmcgahan@internetworkexpert.com>
Date: Wed, 23 Aug 2006 17:34:03
To:"Rick Fox" <rick.fox@tcsna.com>,<ccielab@groupstudy.com>
Subject: RE: ICMP snooping on non-routed VLAN
IGMP snooping is a layer 2 function and doesn't require any
layer 3 configuration on the switch performing it. When a host sends an
IGMP join the switch will hear it and add the appropriate multicast MAC
address to the CAM table for that port. What is the specific problem
you are seeing or trying to solve?
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Rick Fox
> Sent: Wednesday, August 23, 2006 11:15 AM
> To: ccielab@groupstudy.com
> Subject: ICMP snooping on non-routed VLAN
>
> Can IGMP work on a vlan without a routed interface?
>
> Lets say you have multiple multicast servers and receivers sharing a
vlan
> that
> is not routed. With IGMP snooping enabled (default), the recievers do
not
> receive any muticast traffic. When IGMP snooping is disabled, the
> receivers
> receive all the multicast traffic. This can be undesirable as the
> receivers
> should only receive multicast on the groups they join.
>
> There is a command IGMP snooping querier, but this requires creating a
> vlan
> interface and putting an ip address on it.
>
> Any other suggestions?
>
> Thanks.
>
>
_______________________________________________________________________
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