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multicast within a vlan

Platform: WS-C4506-E (MPC8548)
IOS: cat4500e-IPBASEK9-M

There is a VLAN 10 SVI on this switch and the ACL is accounting lots of multicast traffic. The SVI has both primary and secondary range configured.

Vlan 10 has many host in primary and secondary range that is multicast capable.
IGMP snooping is enabled by default.

CS2#show ip igmp snooping vlan 10
Global IGMP Snooping configuration:
IGMP snooping                : Enabled
IGMPv3 snooping (minimal)    : Enabled
Report suppression           : Enabled
TCN solicit query            : Disabled
TCN flood query count        : 2
Robustness variable          : 2
Last member query count      : 2
Last member query interval   : 1000

Vlan 10:
IGMP snooping                       : Enabled
IGMPv2 immediate leave              : Disabled
Multicast router learning mode      : pim-dvmrp
CGMP interoperability mode          : IGMP_ONLY
Robustness variable                 : 2
Last member query count             : 2
Last member query interval          : 1000

I wanted to make sure multicasting within this vlan 10 works without any problem
None of the switchports show a multicast entry. Therefore I am little suspicious that multicast within this vlan is working correctly or not.
I have made no special multicast configuration for this.

Sample log:

Sep 16 06:46:00.299: %SEC-6-IPACCESSLOGRP: list Manufacturing_ACL_190 denied igmp x.x.x.x ->, 1 packet

CS2#show mac address-table multicast
Vlan    Mac Address       Type        Ports
----    -----------       ----        -----


Regards Vinayak
Cisco Employee

multicast within a vlan

Hi Vinayak,

Do you see any group from 'show ip igmp group'? What multiple group are you running in vlan 10? Is it multicast in layer 2 only? How's your SVI confgiured?


Lei Tian

New Member

multicast within a vlan is layer 2 multicast only.

interface Vlan10
description Manufacturing VLAN
ip address x.x.x.x secondary
ip address y.y.y.y
ip access-group Manufacturing_ACL_190 in
standby 10 ip y.y.y.y
standby 10 ip x.x.x.x secondary
standby 10 timers 1 3
standby 10 priority 105
standby 10 preempt
standby 10 name hsrp_mftg_vlan_gw

CS2#show ip igmp groups
IGMP Connected Group Membership
Group Address    Interface                Uptime    Expires   Last Reporter   Group Accounted


Regards Vinayak
Cisco Employee

multicast within a vlan


For multicast in layer 2 only network, you need a router becomes IGMP querier. You can do that by either enable pim under SVI or just enabel IGMP querier. The layer 2 mcast traffic should not hit your interface ACL.


Lei Tian

New Member

multicast within a vlan

Ok...i will study about igmp querier and then configure it..should the end host be aware of who is igmp querier?

even if i have mutlicast between primary and secondary range of same SVI, the igmp packets will not hit my acl?


Regards Vinayak
Super Bronze

Re: multicast within a vlan


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If multicast sender and receiver are within the same L2 broadcast domain, multicast should work unless you're running across a switch that does IGMP snooping.  An IGMP snooper needs an IGMP querier so it will know which ports want to receive the multicast traffic.

Normally multicast router gateway act as an IGMP querier, but some L2 IGMP snooping switches can do this function too.

If I remember correctly, to enable IGMP querier on a L3 interface, just enable PIM in the L3 interface.

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