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HREAP and Multicast traffic

I have a controller sat on a network ( with a management address of  There's a distant site we have at the other side of the network with a range at  I have 5 thin HREAP access points on this network with three WLANs from the controller and one WLAN delivered via a trunk point with VLAN 2 tagging (the network is VLAN1).  The VLAN2 (e.g. network is basically an untrusted network to us , but I didn't think this would matter as the HREAP config would mean that none of this traffic should even leave the access point - apart from stats/client info.

However, i've recently been seeing something odd in that there must be some multicast-talking clients on this untrusted network and whatever they are talking about I can see on my management LAN (  I can basically see multicast packets with source IPs from the untrusted network.  How is this possible?  More importantly how can I stop it?

All network numbers are just examples.  Any help or ideas would be gratefully received.

Everyone's tags (6)
Cisco Employee

Re: HREAP and Multicast traffic

Hi Stuart,

Just to clarify a point:

"but I didn't think this would matter as the HREAP config would mean that  none of this traffic should even leave the access point"

Keep in mind that when an ap is hreap mode, the ap essentially acts like a switch with respect to its ethernet port.  When it gets a packet from the wireless side, if appropriate, it tags it and puts it on the wire.

Under ordinary circumstances (unless something is configured to stop this), if a wireless client connected to an hreap ap sends a multicast packet, it absoutely will be put on the wire by the ap, just as a broadcast would.  I just confirmed this with lab equipment.

So if there isn't a routed path from the remote untrusted networks to your mgmt vlan, there may (should) be L3 multicast routing configured for the untrusted and your management routed interfaces.  Is this the case?



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