Multicast IGMPsnooping problem - TCP-IP

This is a discussion on Multicast IGMPsnooping problem - TCP-IP ; Hi All, I'm having problems with a Layer 3 Ethernet Switch. Basically, it appears to broadcast multicast messages for multicast addresses/groups that have previously not been 'joined' using the IGMP protocol. The obvious effect of this is that the network ...

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Thread: Multicast IGMPsnooping problem

  1. Multicast IGMPsnooping problem

    Hi All,
    I'm having problems with a Layer 3 Ethernet Switch. Basically, it
    appears to broadcast multicast messages for multicast addresses/groups
    that have previously not been 'joined' using the IGMP protocol. The
    obvious effect of this is that the network is flooded.
    The behaviour I'm trying to acheive is to get the switch to only
    forward messages to those ports which have 'joined' the group.

    I thought the problem could be solved by statically creating a new
    multicast group using the switch's config tool, but this doesn't help.
    I have IGMP and IGS (ie. snooping) enabled. It is for a LAN single
    switch setup with no routers.
    The odd thing is that I have a D-Link switch which works perfectly and
    never forwards multicast messages until hosts join, but this switch
    simply behaves differently.

    Has anybody got any ideas?. There are about a million settings in the
    web-based tool for configuration so I guess there might be something
    in there which might change the switches behaviour.

    Regards,
    Dave


  2. Re: Multicast IGMPsnooping problem

    wrote in message
    news:1187958047.769805.138800@i38g2000prf.googlegr oups.com...
    > Hi All,
    > I'm having problems with a Layer 3 Ethernet Switch. Basically, it
    > appears to broadcast multicast messages for multicast addresses/groups
    > that have previously not been 'joined' using the IGMP protocol. The
    > obvious effect of this is that the network is flooded.
    > The behaviour I'm trying to acheive is to get the switch to only
    > forward messages to those ports which have 'joined' the group.
    >
    > I thought the problem could be solved by statically creating a new
    > multicast group using the switch's config tool, but this doesn't help.
    > I have IGMP and IGS (ie. snooping) enabled. It is for a LAN single
    > switch setup with no routers.


    IGMP snooping is intended for a L2 switched network between a bunch of
    devices and a router.

    does your L3 switch understand L3 multicast so it do the logical routing
    function?

    > The odd thing is that I have a D-Link switch which works perfectly and
    > never forwards multicast messages until hosts join, but this switch
    > simply behaves differently.
    >
    > Has anybody got any ideas?. There are about a million settings in the
    > web-based tool for configuration so I guess there might be something
    > in there which might change the switches behaviour.


    sorry - telepathy link is down today.

    switch make / model / s/w version and some idea of how you have it set up?
    >
    > Regards,
    > Dave
    >

    --
    Regards

    stephen_hope@xyzworld.com - replace xyz with ntl



  3. Re: Multicast IGMPsnooping problem

    On 24 Aug, 13:27, "stephen" wrote:
    > wrote in message
    >
    > news:1187958047.769805.138800@i38g2000prf.googlegr oups.com...
    >
    > > Hi All,
    > > I'm having problems with a Layer 3 Ethernet Switch. Basically, it
    > > appears to broadcast multicast messages for multicast addresses/groups
    > > that have previously not been 'joined' using the IGMP protocol. The
    > > obvious effect of this is that the network is flooded.
    > > The behaviour I'm trying to acheive is to get the switch to only
    > > forward messages to those ports which have 'joined' the group.

    >
    > > I thought the problem could be solved by statically creating a new
    > > multicast group using the switch's config tool, but this doesn't help.
    > > I have IGMP and IGS (ie. snooping) enabled. It is for a LAN single
    > > switch setup with no routers.

    >
    > IGMP snooping is intended for a L2 switched network between a bunch of
    > devices and a router.
    >
    > does your L3 switch understand L3 multicast so it do the logical routing
    > function?


    Yes, I believe so. If IGMP join/leave messages are sent then it
    appears to forward the messages correctly. This is confirmed in the
    forwarding table.

    > > The odd thing is that I have a D-Link switch which works perfectly and
    > > never forwards multicast messages until hosts join, but this switch
    > > simply behaves differently.

    >
    > > Has anybody got any ideas?. There are about a million settings in the
    > > web-based tool for configuration so I guess there might be something
    > > in there which might change the switches behaviour.

    >
    > sorry - telepathy link is down today.
    >
    > switch make / model / s/w version and some idea of how you have it set up?


    Very sorry to hear about your misfiring telepathy link. The switch is
    a Curtiss-Wright SwitchBade 680 item and is therefore pretty obscure.
    Basically, the switch has 4-5 PCs plugged into it. No others switches
    or routers.

    Regards



  4. Re: Multicast IGMPsnooping problem

    wrote in message
    news:1187961333.696065.247220@i13g2000prf.googlegr oups.com...
    > On 24 Aug, 13:27, "stephen" wrote:
    > > wrote in message
    > >
    > > news:1187958047.769805.138800@i38g2000prf.googlegr oups.com...
    > >
    > > > Hi All,
    > > > I'm having problems with a Layer 3 Ethernet Switch. Basically, it
    > > > appears to broadcast multicast messages for multicast addresses/groups
    > > > that have previously not been 'joined' using the IGMP protocol. The
    > > > obvious effect of this is that the network is flooded.
    > > > The behaviour I'm trying to acheive is to get the switch to only
    > > > forward messages to those ports which have 'joined' the group.

    > >
    > > > I thought the problem could be solved by statically creating a new
    > > > multicast group using the switch's config tool, but this doesn't help.
    > > > I have IGMP and IGS (ie. snooping) enabled. It is for a LAN single
    > > > switch setup with no routers.

    > >
    > > IGMP snooping is intended for a L2 switched network between a bunch of
    > > devices and a router.
    > >
    > > does your L3 switch understand L3 multicast so it do the logical routing
    > > function?

    >
    > Yes, I believe so. If IGMP join/leave messages are sent then it
    > appears to forward the messages correctly. This is confirmed in the
    > forwarding table.


    maybe you could hook up a multicast capable router to the switch and see if
    it helps?

    it only needs enough processing to handle the IGMP
    >
    > > > The odd thing is that I have a D-Link switch which works perfectly and
    > > > never forwards multicast messages until hosts join, but this switch
    > > > simply behaves differently.

    > >
    > > > Has anybody got any ideas?. There are about a million settings in the
    > > > web-based tool for configuration so I guess there might be something
    > > > in there which might change the switches behaviour.

    > >
    > > sorry - telepathy link is down today.
    > >
    > > switch make / model / s/w version and some idea of how you have it set

    up?
    >
    > Very sorry to hear about your misfiring telepathy link. The switch is
    > a Curtiss-Wright SwitchBade 680 item and is therefore pretty obscure.
    > Basically, the switch has 4-5 PCs plugged into it. No others switches
    > or routers.
    >
    > Regards

    --
    Regards

    stephen_hope@xyzworld.com - replace xyz with ntl



  5. Re: Multicast IGMPsnooping problem

    wrote:

    > On 24 Aug, 13:27, "stephen" wrote:


    >> IGMP snooping is intended for a L2 switched network between a bunch
    >> of
    >> devices and a router.
    >>
    >> does your L3 switch understand L3 multicast so it do the logical
    >> routing
    >> function?

    >
    > Yes, I believe so. If IGMP join/leave messages are sent then it
    > appears to forward the messages correctly. This is confirmed in the
    > forwarding table.


    I think Stephen's point was that the router, what you call "layer 3
    Ethernet switch," should NOT be forwarding any multicast packets from
    another (call it "outside") IP subnet UNLESS someone in the IP subnet in
    question previously sent an IGMP join report to this router.

    So if you're seeing these multicasts reaching the "inside" IP subnet,
    before anyone joined the group, then either the router isn't doing its
    job right, or the source of the multicast is in this "inside" the IP
    subnet.

    Where is the multicast source?

    If the multicast source is in the IP subnet in question, then it is
    acceptable behavior for any Ethernet layer 2 switch to flood that
    multicast to all ports, even if no IGMP join reports occurred.

    Bert


  6. Re: Multicast IGMPsnooping problem

    "Albert Manfredi" wrote in message
    news:JnAL1L.FwB@news.boeing.com...
    > wrote:
    >
    > > On 24 Aug, 13:27, "stephen" wrote:

    >
    > >> IGMP snooping is intended for a L2 switched network between a bunch
    > >> of
    > >> devices and a router.
    > >>
    > >> does your L3 switch understand L3 multicast so it do the logical
    > >> routing
    > >> function?

    > >
    > > Yes, I believe so. If IGMP join/leave messages are sent then it
    > > appears to forward the messages correctly. This is confirmed in the
    > > forwarding table.

    >
    > I think Stephen's point was that the router, what you call "layer 3
    > Ethernet switch," should NOT be forwarding any multicast packets from
    > another (call it "outside") IP subnet UNLESS someone in the IP subnet in
    > question previously sent an IGMP join report to this router.


    a much clearer explanation than i managed
    >
    > So if you're seeing these multicasts reaching the "inside" IP subnet,
    > before anyone joined the group, then either the router isn't doing its
    > job right, or the source of the multicast is in this "inside" the IP
    > subnet.
    >
    > Where is the multicast source?
    >
    > If the multicast source is in the IP subnet in question, then it is
    > acceptable behavior for any Ethernet layer 2 switch to flood that
    > multicast to all ports, even if no IGMP join reports occurred.


    agreed

    but if you have only 1 subnet, and want IGMP snooping to work within that
    subnet, then you may need a router to help the switch figure out where it
    should allow multicast to propagate at layer 2, and where to suppress it.
    >
    > Bert

    --
    Regards

    stephen_hope@xyzworld.com - replace xyz with ntl



  7. Re: Multicast IGMPsnooping problem

    Thanks for your comments.

    > > If the multicast source is in the IP subnet in question, then it is
    > > acceptable behavior for any Ethernet layer 2 switch to flood that
    > > multicast to all ports, even if no IGMP join reports occurred.


    Why is this?. Surely this is unnecessary and annoying?.


  8. Re: Multicast IGMPsnooping problem

    wrote:

    >> > If the multicast source is in the IP subnet in question, then it is
    >> > acceptable behavior for any Ethernet layer 2 switch to flood that
    >> > multicast to all ports, even if no IGMP join reports occurred.

    >
    > Why is this?. Surely this is unnecessary and annoying?.


    If there's no router through which an IP multicast must travel, then in
    principle there won't be any IGMP queries transmitted either. Because
    IGMP queries are transmitted by routers to determine on which of their
    subnets there might be multicast group membership, only to determine
    which multicast packets to forward between IP subnets.

    So any multicast created by a host inside a subnet would potentially be
    unavailable to any other host in that subnet. No router to traverse, no
    need for IGMP queries to ever be sent by anyone, no way for any host to
    receive those packets.

    So the safe thing to do is to flood a multicast that is "unknown."
    Meaning, for which no queries or reports were seen.

    IGMP snooping is a strange beast, where layer 2 boxes look into parts of
    the frame that are none of their business. You can expect strange
    behavior if it's not used exactly as envisioned by the authors of RFC
    4541.

    Bert


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