Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Layer 3 Switch and Multicasts

We have a Cisco 4948 Switch which appears to be sending Multicast traffic outside of its intended VLAN and consequently flooding an external network.  Perhaps I am missing a configuration to restrict this traffic. Can you help?

Thanks,

~~c

3 ACCEPTED SOLUTIONS

Accepted Solutions
New Member

Re: Layer 3 Switch and Multicasts

Hi,

without the config, I can only guess. But you can try to set the storm-control multicast level or see the following page:

https://www.cisco.com/en/US/docs/ios/ipmulti/configuration/guide/imc_cfg_rpgmp_ps6441_TSD_Products_Configuration_Guide_Chapter.html

Maybe it helps you

Regards

Martin

Hall of Fame Super Blue

Re: Layer 3 Switch and Multicasts

gdwingnuts wrote:

We have a Cisco 4948 Switch which appears to be sending Multicast traffic outside of its intended VLAN and consequently flooding an external network.  Perhaps I am missing a configuration to restrict this traffic. Can you help?

Thanks,

~~c

As Jerry says, config would be useful but some questions -

1) Is the 4948 responsible for L3 inter-vlan routing ?

2) if 1) then have you enabled ip multicast routing on the switch

3) if 2) have you enabled PIM on any of the vlan interfaces and if so which PIM, sparse or dense mode ?

4) Do you have any receivers that are not in the intended vlan ?

Be aware that PIM dense mode is a flood and prune technology so it will send the multicast traffic onto any vlan that has PIM enabled. If you want to avoid this you could either -

1) use PIM sparse mode which does not use flood and prune

2) if you only need multicast within the actual vlan then disable multicast routing and use IGMP snooping querier on that L3 vlan interface.

Jon

Cisco Employee

Re: Layer 3 Switch and Multicasts

You can remove sparse-dense-mode on the VLAN that you don't want multicast traffic to be received. To contain the multicast traffic in a single L2 VLAN, you can leave ip pim sparse-dense-mode configured or like what you said, configured igmp snooping querier. This should do the trick.

HTH,

jerry

5 REPLIES
Cisco Employee

Re: Layer 3 Switch and Multicasts

Can you post the config and detail explaining what is happening?

Regards,

jerry

New Member

Re: Layer 3 Switch and Multicasts

Hi,

without the config, I can only guess. But you can try to set the storm-control multicast level or see the following page:

https://www.cisco.com/en/US/docs/ios/ipmulti/configuration/guide/imc_cfg_rpgmp_ps6441_TSD_Products_Configuration_Guide_Chapter.html

Maybe it helps you

Regards

Martin

Hall of Fame Super Blue

Re: Layer 3 Switch and Multicasts

gdwingnuts wrote:

We have a Cisco 4948 Switch which appears to be sending Multicast traffic outside of its intended VLAN and consequently flooding an external network.  Perhaps I am missing a configuration to restrict this traffic. Can you help?

Thanks,

~~c

As Jerry says, config would be useful but some questions -

1) Is the 4948 responsible for L3 inter-vlan routing ?

2) if 1) then have you enabled ip multicast routing on the switch

3) if 2) have you enabled PIM on any of the vlan interfaces and if so which PIM, sparse or dense mode ?

4) Do you have any receivers that are not in the intended vlan ?

Be aware that PIM dense mode is a flood and prune technology so it will send the multicast traffic onto any vlan that has PIM enabled. If you want to avoid this you could either -

1) use PIM sparse mode which does not use flood and prune

2) if you only need multicast within the actual vlan then disable multicast routing and use IGMP snooping querier on that L3 vlan interface.

Jon

New Member

Re: Layer 3 Switch and Multicasts

Jon,

We do have inter vlan routing configured.  We also have ip pim sparse-dense-mode configured on two of the three VLANs.  Just to be clear, if I wanted Multicast within only one VLAN should I remove the ip pim sparse-dense-mode from other VLAN interfaces, and then enable IGMP snooping querier on that VLAN interface as well?  Also, I have found the problem with the unwanted traffic.  An engineer connected to the wrong VLAN.  Actually he connected to the VLAN which has the Multicast Traffic.  I guess it was user error in this case.  Thanks for the useful information.

Cisco Employee

Re: Layer 3 Switch and Multicasts

You can remove sparse-dense-mode on the VLAN that you don't want multicast traffic to be received. To contain the multicast traffic in a single L2 VLAN, you can leave ip pim sparse-dense-mode configured or like what you said, configured igmp snooping querier. This should do the trick.

HTH,

jerry

464
Views
0
Helpful
5
Replies