Re: OT: WLC & ARP

Yes, I have seen that command as well, but what about an initial ARP
request. Say I ARP for 10.0.0.1. That ARP request is a L2 broadcast. How
does the WLC know what client to unicast it to? Based on client
associations with an AP? (It could know the MAC address from that). If that
is the case, what about ARPs for unknown clients. Would they be dropped or
somehow "flooded" like a traditional bridge?

On Wed, Oct 26, 2011 at 2:17 PM, Thomas Perrier <thomas_at_perrier.name> wrote:

> Hi Joe,
>
> On Wed, Oct 26, 2011 at 7:36 PM, Joe Astorino <joeastorino1982_at_gmail.com>
> wrote:
> > I have been searching on this topic for a while but can't find a specific
> > answer. Does anybody know how a Cisco WLC handles ARP broadcasts for
> > wireless clients? Let's say a user on the wired network wants to talk to
> a
> > wireless client. You have a WLC connected to a L3 switch somewhere in
> your
> > infrastructure and several LWAPs. The packet gets routed to the L3
> switch,
> > and the L3 switch has a directly connected L3 interface for the client
> where
> > the WLC lives. At this point the L3 switch does an ARP broadcast to find
> > the MAC address of the wireless client. That broadcast gets to the WLC
> --
> > Now what?
> >
> > It doesn't seem to make sense that the WLC would forward the ARP
> broadcast
> > over an LWAP tunnel to EVERY access point and that the access points
> would
> > then forward it to every client. So, what happens? Is it some sort of
> > proxy arpish type thing the WLC does? Things I have read so far seem to
> > indicate that the WLC answers the ARP request with the MAC of the client,
> as
> > it knows the MAC from when the client associated with the remote AP but I
> > can't find anything that specifically confirms this.
>
> Found in "Deploying and Troubleshooting Cisco Wireless LAN
> Controllers" (Cisco Press) :
>
> "Should ARP unicast be enabled, you can disable it using the following
> CLI command:
> config network arpunicast disable
> If ARP unicast is enabled, the controller responds to an ARP query on
> behalf of the client instead of unicasting the request directly to the
> target host. This behavior can cause one-way audio with voice clients.
> Starting in the 5.1 code release, this command is deprecated.
> Furthermore, the proxy ARP nature of the controller cannot be modified
> and is always turned off."
>
> What I understand from this, is that in later releases the WLC
> unicasts ARP requests directly to the right client (since proxy ARP is
> turned off). It would be interesting to lab it some day in order to
> verify this behaviour.
>
> -Thomas
>

-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
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