SM Isolation Clarification

I need some better clarification on SM Isolation. According to the User guie the following are the choices:

SM Isolation
Prevent or allow SM-to-SM communication by selecting from the following drop-down
menu items:

◦ Disable SM Isolation (the default selection). This allows full communication
between SMs.

◦ Block SM Packets from being forwarded. This prevents both
multicast/broadcast and unicast SM-to-SM communication.

◦ Block and Forward SM Packets to Backbone. This not only prevents
multicast/broadcast and unicast SM-to-SM communication but also sends the packets, which otherwise would have been handled SM to SM, through the Ethernet port of the AP.

What would be the advantage/disadvantage for using Block SM packets from being forwarded vs. Block and Forward? Why would I want to forward the packets to the backbone? Would I do that if running VLAN’s and had a VLAN switch at the tower or main tower site?


Blocking the packets from being forwarded means that if SM1 and SM2 are both on AP1, then will be unable to communicate directly with one another. This can be useful to eliminate chatter and broadcast traffic on an AP.

Block and forward would forward it to your routers. You could create rules to allow certain SMs the ability to communicate with one another (say if you’re providing two branch offices of a company service so they can communicate via their computer network).

If I want to define VLANS and do NOT choose to forward packets won’t this break the VLAN? I have not decided which way to go with design Route or Vlan, but in my head if I don’t “forward SM destined packets upstream” then my vlans will break?

Depending on how you’ve deployed VLANs, I would assume there is a possibility it could foul them up in certain situations (as like mentioned above where two SMs on a single AP share a VLAN and need to communicate).

I’ve left my settings to disable SM isolation. I’ve never really seen a performance hit with SM isolation off, so I don’t see a reason to enable it at this point.