Solved: switchport block multicast

tedauction · ‎07-26-2017

Hello, as part of our normal switch build I notice these two commands are to be placed on every switch access port:

switchport block multicast

no ip igmp snooping tcn flood

Are these two commands really necessary or recommended as standard procedure to put on a switchport ?

We do use multicast traffic on our LAN for certain ports.

Thanks kindly for any advice.

Reza Sharifi · ‎07-27-2017

Hi,

I think it is good idea to have these commands in your basic config.

Occasionally, unknown unicast or multicast traffic is flooded to a switch port because a MAC address has timed out or has not been learned by the switch. (This condition is especially undesirable for a private VLAN isolated port.) To guarantee that no unicast and multicast traffic is flooded to the port, use the switchport block unicast and switchport block multicast commands to enable flood blocking on the switch.

link:

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/31sg/configuration/guide/conf/uniflood.html

With the no ip igmp snooping tcn flood command, you can disable multicast flooding on a switch interface following a topology change. Only the multicast groups that have been joined by a port are sent to that port, even during a topology change.

link:

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/53SG/configuration/config/multi.html

HTH

View solution in original post

Reza Sharifi · ‎07-27-2017

Hi,

I think it is good idea to have these commands in your basic config.

Occasionally, unknown unicast or multicast traffic is flooded to a switch port because a MAC address has timed out or has not been learned by the switch. (This condition is especially undesirable for a private VLAN isolated port.) To guarantee that no unicast and multicast traffic is flooded to the port, use the switchport block unicast and switchport block multicast commands to enable flood blocking on the switch.

link:

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/31sg/configuration/guide/conf/uniflood.html

With the no ip igmp snooping tcn flood command, you can disable multicast flooding on a switch interface following a topology change. Only the multicast groups that have been joined by a port are sent to that port, even during a topology change.

link:

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/53SG/configuration/config/multi.html

HTH