said by nranieri:
Sorry, maybe I am missing something obvious, but what would DHCP lease times have to do with this? The problem will happen if the client in question is connected for just a few seconds. They will remain there til I find them, but the interface will stop forwarding almost immediately.
Maybe nothing, but, curiously, I have a friend that notice similar behavior on one of his hotspots...this just happened last week.
He has a newly installed hotspot overlooking a small city park (one square block) using a UniFi radio. He noticed that after a while new customers would connect, but not authenticate and pass traffic to the internet.
He gets a lot of client churn, maybe 40-60 unique clients per day at this location.
We looked at -all- of the configuration items at length. The only thing that we noticed was that the lease time was set to one week.
Since most visits are only in the one hour or less range we set the lease time to one hour.
That seems to have solved the problem, such as it is. I am not sure what the underlying issue is, as this falls outside of my area of expertise. That being said, I won't let that stop me from making a wild guess as to what I think is happening.
Please excuse my 'mechanistic' approach to describing the problem...
The AP is like a building on a city street. At the door is a doorman that lets you in if you qualify (you're an 802.11 packet). You enter into the holding area (connected but not authenticated). You go up to the turnstile where you wait to be authorized to join the party (pass traffic). The party is musical chairs, and there are only so many chairs available (DHCP allocations). You have to wait at the turnstile until a seat is available. The turnstile attendant checks the tickets of the players every "lease period", in your case every week, to look for players who's lease has expired, removes those players and lets another new player in the turnstile to take a chair (allocates a DHCP slot and issues an IP address).
Since the lease period is one week, the system does not process that lease expiry until the time period is up. Consequently, there can be no issuance of new leases until slots are available. The pending connection sits and waits.
In most instances in typical WISP operation, you may not see the full utilization of the DHCP table as most clients stay connected on a typical POP. When an AP is used in hotspot service, however, there is a lot of client churn, and the table might be filled to capacity. There may be a structural programming design implementation limitation (or bug!) in the firmware that does not adequately address the full DHCP table issue. I would imagine that there are a number of different ways to handle it programming-wise, some good and others not-so-good.
Don't know...! Again, this falls outside of my area of expertise. I simply regard it as a 'black box' where things happen and I can't see what is happening.
Getting back to our particular experience...when we reset the DHCP lease time to one hour, the problem seemingly resolved itself. From that, I'd suspect that when the leases are forced and renewed at the end of the DHCP lease set time, it boots the unconnected stations off the list and issues new leases and connects. The housekeeping is done and there are always DHCP lease allocations available.
There is a point at which the lease time is too short and causes issues, but in this venue I think that one hour is reasonable based on the expected client connect times.
We are keeping an eye on the AP and this weekend might be a good time to see heavy loading...weather permitting for a trip to the park on Labor Day.
At any rate, that is why I suggested shortening the lease time.
's suggestion of limiting the rates and enforcing minimum signal levels would be beneficial also. I don't believe in setting up APs to be "alligator stations"...all mouth and no ears. The transmit power should be set to be equal to the APs ability to hear those clients. Utilizing a lower output power causes the clients to move into the service area where the AP can adequately hear the client, and this eliminates much of the 'thrash and bash' as the weak clients trying to negotiate a session with the AP.--
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