IGMP querying without multicast routing

Discussion in 'Cisco' started by googlegroups@marget.com, Feb 12, 2007.

  1. Guest

    Greetings!

    I'm working with a Catalyst 4948 running 12.2(25)EWA4.

    The 4948 is sliced into several VLANs, each with several directly
    connected hosts. The 4948 has an IP address configured in each of
    those VLANs.

    There's no routing going on here. These VLANs are used for multicasts
    which I do not want to escape the broadcast domain.

    IGMP snooping is enabled (by default), but isn't learning anything
    because none of the VLANs have a querier.

    So, the question is: How can I enable querying without enabling
    routing on these VLAN interfaces?

    I'd expected that this would do it:
    (config-if)# ip igmp snooping querier

    But that command isn't available.

    Tips?

    Thank you.

    /chris
    , Feb 12, 2007
    #1
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  2. Thrill5 Guest

    IGMP snooping may not be available on the 4948. Snooping by design is
    passive, it only listens for IGMP messages to determine what multicasts need
    to be enabled on a port. IGMP snooping is also a layer 2 service, and
    having an IP address on a VLAN is not a requirement to make it work.

    Scott
    <> wrote in message
    news:...
    > Greetings!
    >
    > I'm working with a Catalyst 4948 running 12.2(25)EWA4.
    >
    > The 4948 is sliced into several VLANs, each with several directly
    > connected hosts. The 4948 has an IP address configured in each of
    > those VLANs.
    >
    > There's no routing going on here. These VLANs are used for multicasts
    > which I do not want to escape the broadcast domain.
    >
    > IGMP snooping is enabled (by default), but isn't learning anything
    > because none of the VLANs have a querier.
    >
    > So, the question is: How can I enable querying without enabling
    > routing on these VLAN interfaces?
    >
    > I'd expected that this would do it:
    > (config-if)# ip igmp snooping querier
    >
    > But that command isn't available.
    >
    > Tips?
    >
    > Thank you.
    >
    > /chris
    >
    Thrill5, Feb 14, 2007
    #2
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  3. Guest

    On 14 Feb, 05:05, "Thrill5" <> wrote:
    > Scott<> wrote in message
    >
    > news:...
    >
    >
    >
    > > Greetings!

    >
    > > I'm working with a Catalyst 4948 running 12.2(25)EWA4.

    >
    > > The 4948 is sliced into several VLANs, each with several directly
    > > connected hosts. The 4948 has an IP address configured in each of
    > > those VLANs.

    >
    > > There's no routing going on here. These VLANs are used for multicasts
    > > which I do not want to escape the broadcast domain.

    >
    > > IGMP snooping is enabled (by default), but isn't learning anything
    > > because none of the VLANs have a querier.

    >
    > > So, the question is: How can I enable querying without enabling
    > > routing on these VLAN interfaces?

    >
    > > I'd expected that this would do it:
    > > (config-if)# ip igmp snooping querier

    >
    > > But that command isn't available.


    > IGMP snooping may not be available on the 4948. Snooping by design is
    > passive, it only listens for IGMP messages to determine what multicasts need
    > to be enabled on a port. IGMP snooping is also a layer 2 service, and
    > having an IP address on a VLAN is not a requirement to make it work.


    Hmmm.

    A routed interface on the same VLAN (anywhere on the VLAN) is in fact
    required for igmp. The exception being that "ip igmp snooping querier"
    allows a L2 box to substitute for the normal L3 interface.

    I would be astonished if the 4948 did not do igmp snooping.

    If you don't have a sperate router maybe:-
    you could configure L3 on the 4948 but turn off "IP routing". Then
    just maybe you would get the required response from the L3
    interfaces.


    no ip routing
    int vl x
    ip address x.x.x.x
    ip pim sparse ! maybe you need or don't need this.
    , Feb 14, 2007
    #3
  4. Guest

    On Feb 14, 12:05 am, "Thrill5" <> wrote:
    > IGMPsnoopingmay not be available on the 4948. Snoopingby design is
    > passive, it only listens for IGMP messages to determine what multicasts need
    > to be enabled on a port. IGMPsnoopingis also a layer 2 service, and
    > having an IP address on a VLAN is not a requirement to make it work.


    Thanks.

    IGMP snooping is certainly available on this box. In fact, it's
    enabled by default (as I said).

    The problem isn't that I can't get snooping to work -- it works fine.

    I can't get *querying* to work. Having an IP address on the VLAN
    (probably) is required to send queries. They're IP packets afterall.
    They have to have a source address.

    /chris
    , Feb 14, 2007
    #4
  5. Guest

    > If you don't have a sperate router maybe:-
    > you could configure L3 on the 4948 but turn off "IP routing". Then
    > just maybe you would get the required response from the L3
    > interfaces.
    >
    > no ip routing
    > int vl x
    > ip address x.x.x.x
    > ip pim sparse ! maybe you need or don't need this


    That's getting very close to what I'm looking for: The minimal config
    to enable querying, but without forwarding any packets from one VLAN
    to another.

    And I think I may have stumbled onto the answer, but am unable to test
    anymore right now:
    ip multicast-routing
    ....but without pim (or any other routing protocol) enabled on any of
    the interfaces.

    I think that's enough to get the supporting infrastructure (including
    querying) up and running, but with no routing protocols, the packets
    can't go anywhere.

    Thanks very much!

    /chris
    , Feb 14, 2007
    #5
  6. Thrill5 Guest

    I have no idea what you are trying to do here, but I will take a stab to
    help you. If the source and destination multicast devices are on the same
    VLAN, all you need it IGMP snooping enabled. (You need to read up on what
    IGMP is and why IGMP snooping is required in a switching environment)
    Multicast routing and IP routing are needed if the source and destination
    devices are on different VLANs. If everything is on the same switch/router
    you won't need a routing protocol or PIM, but routing will be turned on and
    traffic routed between VLANs because all the VLANs are directly connected.

    Scott


    <> wrote in message
    news:...
    >> If you don't have a sperate router maybe:-
    >> you could configure L3 on the 4948 but turn off "IP routing". Then
    >> just maybe you would get the required response from the L3
    >> interfaces.
    >>
    >> no ip routing
    >> int vl x
    >> ip address x.x.x.x
    >> ip pim sparse ! maybe you need or don't need this

    >
    > That's getting very close to what I'm looking for: The minimal config
    > to enable querying, but without forwarding any packets from one VLAN
    > to another.
    >
    > And I think I may have stumbled onto the answer, but am unable to test
    > anymore right now:
    > ip multicast-routing
    > ...but without pim (or any other routing protocol) enabled on any of
    > the interfaces.
    >
    > I think that's enough to get the supporting infrastructure (including
    > querying) up and running, but with no routing protocols, the packets
    > can't go anywhere.
    >
    > Thanks very much!
    >
    > /chris
    >
    Thrill5, Feb 15, 2007
    #6
  7. Guest

    On Feb 14, 10:21 pm, "Thrill5" <> wrote:
    > I have no idea what you are trying to do here, but I will take a stab to
    > help you.


    I'm trying to make a 4948 send IGMP queries.

    > If the source and destination multicast devices are on the same
    > VLAN, all you need it IGMP snooping enabled.


    If I want IGMP snooping to *work*, your recipe is one ingredient
    short. It also needs an IGMP querier. Without queries, there will be
    no IGMP traffic beyond the initial host report, so IGMP snooping will
    have nothing to eavesdrop upon.

    > (You need to read up on what
    > IGMP is and why IGMP snooping is required in a switching environment)


    Oh my.

    > If everything is on the same switch/router
    > you won't need a routing protocol or PIM


    Sending IGMP queries is a *router* function. It's part of the IGMP2
    specification, and is definitely not an the job of an L2 switch.
    Right now my switch (even with an interface on the VLAN) is just an L2
    switch.

    It appears that I need to enable some subset of multicast-routing
    functionality in order to get the switch to send queries. I just want
    to enable only the minimum functionality so that multicast traffic
    doesn't get routed between VLANs.

    This question really isn't a protocol question. It's a Cisco
    implementation question.
    , Feb 15, 2007
    #7
  8. HotKompost

    Joined:
    Oct 20, 2008
    Messages:
    1
    Available fix ?

    Hi,

    running into the same kind of problem. Just using a single Cisco switch 4500E or 6500E to forward L2 multicast in a single VLAN. Enabling IP multicast-routing and PIM seems to start of the igmp querier. But when doing so the DR/RP traffic causes the CPU to be hit massively by the multicast traffic itself.

    So.. short question.. did anybody solve this issue (long time ago) -or- is this still an open thread ???

    Thx.

    G-Kompost
    HotKompost, Oct 20, 2008
    #8
  9. icejam

    Joined:
    Apr 10, 2007
    Messages:
    2
    thought this could fix it???

    Enabling the IGMP Snooping Querier

    Use the IGMP snooping querier to support IGMP snooping in a VLAN where PIM and IGMP are not configured because the multicast traffic does not need to be routed.

    To enable the IGMP snooping querier in a VLAN, perform this task:

    Step 1
    Router(config)# interface vlan vlan_ID
    #Selects the VLAN interface.

    Step 2
    Router(config-if)# ip address ip_address subnet_mask
    #Configures the IP address and IP subnet.

    Step 3
    Router(config-if)# ip igmp snooping querier
    #Enables the IGMP snooping querier.

    Router(config-if)# no ip igmp snooping querier
    #Disables the IGMP snooping querier.

    Step 4
    Router(config-if)# end
    #Exits configuration mode.

    Step 5
    Router# show ip igmp interface vlan vlan_ID | include querier
    #Verifies the configuration.

    This example shows how to enable the IGMP snooping querier on VLAN 200 and verify the configuration:

    Router# interface vlan 200
    Router(config-if)# ip address 172.20.52.106 255.255.255.248
    Router(config-if)# igmp snooping querier
    Router(config-if)# end
    Router# show ip igmp interface vlan 200 | include querier
    IGMP snooping fast-leave (for v2) is disabled and querier is enabled
    icejam, Mar 8, 2010
    #9
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