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AC2600 and DHCP management
Hi everybody.
I have extended a wifi network in a school, and i have used for that, 4 AC2600, in AP mode, and the modem/router is managing the DHCP.
Everything work fine while there is not to...
PatDen wrote:
Not with simply routers i présume.. ?????Correct. These are generally dedicated SERVERS with many ISP lines coming into them depending on requirements. Think of them as large modems that do DHCP. They are fed by wireless access point/repeaters located in various places.
Coffee shops and other local retail places might use a single router depending on the size of the store, as they might assume less than 250 devices connecting at the same time, but they would more then likely have better routers than your standard run of the mill Residential models. ISP speeds would also likely be higher as well.
The basic problem will always be the number of users at one time and the available bandwidth.
it normally should be able. but there's a possibility of DHCP pool exhaustion as NG uses 1 day for lease time. If many devices come and go quickly, it can run out of addresses
Suspect that microchip8 hit on the problem. If you have a number of clients coming and going then the 1 day lease time is probably not a good setting. May want to try 12 hours or even lower. Any devices that are currently connected will stay connected, just renew their lease.
myersw wrote:
Suspect that microchip8 hit on the problem. If you have a number of clients coming and going then the 1 day lease time is probably not a good setting. May want to try 12 hours or even lower. Any devices that are currently connected will stay connected, just renew their lease.
Bill, the devices are the ones that set the lease time. As far as I know no Netgear router determines the device lease time. Changing the lease time can be done, but not all OS's allow that, at least not easily.
Usually that wouldn't be a problem. In olden days when there was dial-up a Least Recently Used list was kept of those attaching. When you dialed in you wound up on a server that had only so many connections available. Once the connections were all make, it searched the list for the oldest connection and dropped that. Worked well because many people stayed connected but not using it at all.
Some ISP's that do not have 'always on' connections (Cable ones do mostly) as some people power down modems when not in use or on vacation. They might plan for that to save needing servers.
So there are 3 questions at work here:
- First and foremost, does Netgear Residential Router use LRU lists and drop an IP Address when 253 are given out and uses the first one on to give to the new connection?
- Does the Netgear router put the IP Address back in the available pool when a device disconnects (is turned off or leaves)?
- Does the OP have more that 253 possible connections?
Hard to say what is going on without 'knowing' those answers I'd say.
This is a clue here, "When more than 20 devices are connected, the modem / router overloads, and no more the internet." First the statement "no more the Internet" is a completely different problem, especially if ALL devices lose it? Secondly, only 20 devices is all it takes to make this happen? Heck, a lot of people would be complaining if this were the case. Yeah, we know Access lists are limited (I think I saw 30 devices?) but not 20 connections.
Modem/Router combo (of unknown make and model) was handling DHCP it seems. It might be the culprit though? Only caveat I can see that would cause problems is the number of expected connections and the ISP speed... and it could be a real problem if the ISP speed is low and a lot of wireless devices connect and are active at the same time. Residential Routers probably can't handle that sort of load.
Last I knew the dhcp server set the lease time. The router has the dhcp server.
> [...] i have used for that, 4 AC2600, in AP mode, and the modem/router
> is managing the DHCP.
What is your "the modem/router"?
> When more than 20 devices are connected, the modem / router overloads,
> and no more the internet.
What, exactly, do you observe when there is "no more the internet"?
How do you know that the problem is related to DHCP?
> [...] the devices are the ones that set the lease time. [...]
No.
> [...] the dhcp server set the lease time.
Yes. And a typical Netgear router does not let the user change its
default (24h) lease time. So, again, what is your "the modem/router"?
20 client devices is not a large number. But, as the others have
said, if many different client devices connect at different times, the
DHCP server may have problems, even if only 20 client devices are
connected at any one time.
myersw wrote:
Suspect that microchip8 hit on the problem. If you have a number of clients coming and going then the 1 day lease time is probably not a good setting. May want to try 12 hours or even lower. Any devices that are currently connected will stay connected, just renew their lease.
Is it possible to manage the lease time in the R7800 ????
yes it's possible. Entable Telnet at http://192.168.1.1/debug.htm
login in Telnet with your pass (telnet 192.168.1.1) and modify the file /tmp/udhcpd.conf file with "vi". Look for "option lease" which is in seconds and set your custom value. Then "killall udhcpd" and start it back again with udhcpd /tmp/udhcpd.conf
What good do you think changing the lease time would be?
Lease time determines when the device would ask for an IP Address. Generally this would be 1/2 the time of the lease. It could be longer, but not by much depending on the load of the device. Say it is set for 24 hours (usual default). At 12 hours the device requests a new lease. Almost ALL the times it will get the same IP Address for 24 hours. If you make the lease 2 hours, then the request comes in at 1 hour and a new 2 hour lease is given. OK, that does set the release of the IP Address to 2 hours IF no new RENEW request has come in and it is returned to the pool.
Good it you want to do that. However there is ONE assumption that you don't know the answer of? The question is DOES the DHCP server/Router manage the pool in such a way that it knows which IP Address as the oldest inactive one to use the address? If it did, the oldest one that didn't use the IP Address, that address would be dropped for that user and given to a new user asking for an IP Address (based on MAC Address of the user).
So the real question IS how many IP Addresses would be used at the SAME TIME. That is NOT the same as CONNECTED at the same time. Now once you had that, could you tell HOW LONG they needed the IP Address?
What I mean is you'll have 180 users at most active for 3 hours. Great, you could set the least time to 7 hours and you'd be all set. Now say the answer is 220 users active for 1/2 hour. That could be a problem. First you are approaching the limit of available IP Addresses at any one time (254) and the shortness of the lease time.
On top of that you really don't know what the router does after it exhausts the DHCP pool. Does it reject all new connection attampts? Does it tell the user why? Does it knock someone who is inactive off?
What you might require is a far more complex system to handle something for possibly the number of ALL users you could expect.
It feels to me like this is begging for a solution based on equipment toward the commerical grade. It sounds like things are being stressed currently and am sure requests/requirements will only increase in a school environment especially since you say your Internet speed is scheduled to be increased.
I have overkilled my home, but things just work. Made up of Ubiquiti Unifi gateway Pro4 with UnfI AP-LR AP's. If you watch Ebay you might pick one up there, that is where I got my gateway.
UNDERSTAND this is a suggestion!
You could start with the Unifi security gateway pro4 and insert it into your existing network in place of the current router/dhcp server. Would give you much more control over dhcp as well as other things. You do have to install a controller application, but it will run on windows. The controller also gives lots of graphs of total bandwidth used, total by application and can drill down to an individual IP address and see what applications are taking how much bandwidth. Does take more effort and knowledge to setup that a consumer grade dumbed down router.
Link to how you would do the swap. https://help.ubnt.com/hc/en-us/articles/236281367-UniFi-USG-How-to-Adopt-a-USG-into-an-Existing-Network