Re: AC2600 and DHCP management

PatDen · ‎2019-01-08

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 much users connected

When more than 20 devices are connected, the modem / router overloads, and no more the internet.

I will try another configuration, i will place de modem in bridge mode, and use my first AC2600 like a router to manage the DHCP to the other AC2600 in AP mode.

Here is my question, do you think that the Nighthawk will be able to manage a lot of request of connection with his DHCP ?

Thanks a lot...... ( and sorry for my poor English language)

IrvSp · ‎2019-01-09

@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.

View solution in original post

microchip8 · ‎2019-01-08

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

myersw · ‎2019-01-08

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.

IrvSp · ‎2019-01-08

@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.

myersw · ‎2019-01-08

Last I knew the dhcp server set the lease time. The router has the dhcp server.

antinode · ‎2019-01-08

> [...] 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.

PatDen · ‎2019-01-08

Hi..

@antinode wrote:

> [...] 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.

Hi

There is a lot of answer and a lot of question ... I have no much time now to answer and i'll come back tonight, bur i can first give the model of the gateway : https://www.mtlcable.cz/other/Technicolor_TC7210_datasheet.pdf

Thank a lot for your attention, and i will come back tonight to explain my exact situation, because, it's not so simple Thanks

antinode · ‎2019-01-08

> [...] Technicolor TC7210 [...]

   Ok. That's a cable-TV modem+router. If your problem really is with
DHCP, then you will need to deal with that device. (Access points
should be too stupid to cause a DHCP problem.)

> I will try another configuration, i will place de modem in bridge
> mode, and use my first AC2600 like a router to manage the DHCP to the
> other AC2600 in AP mode.

   I would not bet that an AC2600 will do any better than the TC7210.
And, if the problem is with DHCP leases which last too long, then I
doubt that you could change the lease time on an AC2600. (I don't know
if you can do it on the TC7210, but I'm pretty confident that you can't
do it on the AC2600.)

> [...] it's not so simple

   Everything's complicated. (Sometimes you might think that it's not,
but you'd be wrong.)

IrvSp · ‎2019-01-09

@myersw wrote:

Last I knew the dhcp server set the lease time. The router has the dhcp server.

Correct, I don't know why I said that? I was probably thinking of a server? I was sober when I posted that? Senior moment

The rest of the post holds though. It might be possible to get into the firmware using TFTP or telnet interface and change the default 24 hours to something smaller as it is a variable held in NVRAM if it could be located and somehow changed I guess? Hmm, see HERE as there was a question about this.

Possible some routers have an option for lease time too?

myersw · ‎2019-01-09

@IrvSp

Not sure about consumer grade router vendors and ability to set lease time. Most of my consumer grade routers were running OpenWRT/LEDE or DD-WRT both of which allow you to change the lease time to whatever you want. Started with DD-WRT on a WRT54G back in 2006. DD-WRT usually ran better then the OEM firmware for me until the r8000. Of course these 3rd party firmware folks are trying to take a consumer grade router to the next level. If you are wondering about the r8000 I had with crappy Netgear firmware, it was the crappy firmware that drove me to try DD-WRT on it. Still had what appeared to be driver issues with DD-WRT, therefore my personal opinion that a big part of the r8xxxx and r9000 router issues are due to the binary blobs that BroadCom provides Netgear. They would be providing DD-WRT with them as well as Brainslayer has a license with Broadcom, which you need.

Ability to set lease time exists on my Ubiquiti gateway (their name for router).

PatDen · ‎2019-01-09

Hello

I try to explain my situation, for that i have made 2 diagrams. ,Diagram 1 is the situation before my incoming in the school.

The internet network was made from a connection with a bandwith =10Mbps trough routers et one PA , the DHCP was activated on each router, then each router made his own network with his DHCP.

PatDen · ‎2019-01-09

The second diagram is the situation now, i have extended the wifi network for différent reasons (the school work with interactive board etc...)

And to have a better bandwith, we must work with the TV cable because the school is to far from town And there is no optical fiber. We have now a bandwith = 125 Mbps and soon we will be with 400 Mbps.

I have configured all the routers in acces point , and so i can manage all of them from 1 computer.

But now each device who try to connect to the network ask his IP to de Modem/router, and sometimes there is no more connection to internet, and we must reboot the Modem/router, i think there is sometimes to much devices to mange for the DHCP of the modem router.

PatDen · ‎2019-01-09

I'm not really a network specialist, i was in the army as technician spécialised for télécom and now i try to help the school where my daughter work as teacher.

I have another asking: The different HOTSPOTs (airport,town Etc...) they are able to connect a lot and a lot of devices, how do they make the management of the DHCP ???? Not with simply routers i présume.. ?????

Thanks everybody for your answers and your attention

IrvSp · ‎2019-01-09

@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.

PatDen · ‎2019-01-19

@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 ????

microchip8 · ‎2019-01-19

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

IrvSp · ‎2019-01-19

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.

myersw · ‎2019-01-19

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-Netw...

PatDen · ‎2019-01-19

It is certainly a better solution than a usual router, but the school has bought 8 Netgear R7800 to set up its wifi network, and I think the budget is empty now. Then, at first, I have to try to work with the NG routers. But I keep your solution as a possibility of "last chance".

Thaks a lot