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Super Contributor I

Broadcast Filtering - ARP

Good morning guys,

 

I have a question about when Broadcast Filtering is set to ARP. User Guide says:

 

  • ARP—When set to ARP, the IAP drops all broadcast and multicast frames except DHCP and ARP, IGMP group queries, and IPv6 neighbor discovery protocols and additionally converts ARP requests to unicast and send frames directly to the associated client.

When it says "converts ARP requests to unicast and send frames directly to the associated client." How is this carried out? Does the IAP look at its ARP table and then convert the broadcast to unicast regarding the destination IP for which the MAC adress is being searched?

Frequent Contributor I

Re: Broadcast Filtering - ARP

hi Julián

effectively yes, the iAP (or controller) knows what it's associated clients are from both an IP and mac address view (see 'show datapath user' rather than 'show arp'), if a frame is received that needs to be bcast (or indeed mcast in some cases) and the client is known, then the datapath will convert the frame to unicast and send it out using a normal tx rate, as opposed to a generally lower speed basic rate.

hth.

Super Contributor I

Re: Broadcast Filtering - ARP

Hi dugem2016,,

 

 

Thanks for the clarification!

Super Contributor I

Re: Broadcast Filtering - ARP

Hi dugem2016,

 

One more question about that:

 

  • ARP—When set to ARP, the IAP drops all broadcast and multicast frames except DHCP and ARP, IGMP group queries, and IPv6 neighbor discovery protocols and additionally converts ARP requests to unicast and send frames directly to the associated client.

What is the benefit of convert an ARP request to unicast?

 

  1. If it is not converted, it is sent as a broadcast at a lower speed basic rate, all the stations will hear it, and only the station which is destined for will reply.
  2. If it is converted, it is sent as an unicast at a normal transmit rate, and only the station which is destined for will hear it and will reply.

The only benefit I see is if it is converted to unicast (point 2), the frame is sent faster and will take less airtime, is that the only benefit?

Frequent Contributor I

Re: Broadcast Filtering - ARP

sorry for the delay in replying...

 

 

The only benefit I see is if it is converted to unicast (point 2), the frame is sent faster and will take less airtime, is that the only benefit?

yes - that's basically it. You can also consider also that in a network of N x APs, that bcast frame will flood out all N x APs, now it's just 1 AP, and unicast at a higher tx rate at that.

 

 

 

If it is not converted, it is sent as a broadcast at a lower speed basic rate, all the stations will hear it, and only the station which is destined for will reply.

also consider the fact that said bcast packet may actually have nothing that will reply, so it's just wasting air time for nothing.

 

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