Forum :: Lounge 2.0 :: dd-wrt lan ip management

Hi guys,

I'm a little confused regarding how the DD-WRT router firmware (pointing at DLINK) manages their LAN ip addresses.  The ip address your device gets when you connect to your router.

When you disconnect from that router does that IP address stay assigned to your device despite being disconnected? Or does that IP go back into the pool for another device to select?

Basically where I work, our tech center has many computers/devices connected to it.  Eventually we start to have an issue where we can't connect new devices after a month of using it.  The manager recently installed a new router in hopes that it solves the issue however; i think it's more of an LAN IP issue, where theirs devices from the past that may still have an IP assigned to it, and due to that reason i think it's running out of IP addresses to assign.

Anyone wanna give their 2 cents on this matter?  I'll be downloading the DD-WRT source tomorrow when i have the time to see how it manages this stuff, but any ideas would be more then welcome :).

When I was in school, our university had a Class B public IP address space. They used public IPs for EVERYTHING and were constantly running out of addresses as more people connected more devices to WiFi. Terribly managed network, but it sounds like the same problem you're having.

The way it works with DHCP is that a device will send out DHCP request packets upon connecting to the network. If a DHCP server responds, it will give out the next available address to the device (if no server responds the device gets a 169.254.x.x address). However - when the device disconnects, that address is still reserved for the device based on the dhcp lease time, which is configurable on the server. It won't go back into the DHCP "pool" until it hits a timeout. Once the timeout is reached, the DHCP server will see if the device is still connected, and if it isn't, it will put the address back in the pool to be re-used by another device.

You have a couple of options to solve it:

1. Lower the lease time for DHCP leases - this will ensure that old addresses that are no longer in use are freed back into the DHCP pool sooner (this is the solution our university used)

2. Use a different private IP address space - if you're using a /24 you're limited to 254 addresses (excluding gateway/broadcast address for the subnet). Assuming you're on a 192.168.x.x address, you could change your subnet to a larger mask like /23 (510 addresses) or /22 (1022 address) and have more space available.

3. Use IPv6 - I know IPv4 is easier, but IPv6 exists for the larger address space. I explicitly disable it on my home network since I don't need it, but it was invented to solve exactly this problem of running out of addresses. You'll need to enable a 6to4 tunnel of some kind at your gateway if your network's public IP is IPv4, which it probably is, so this is the most pain-in-the-ass option you can go with.

Looking at the source code of DD-WRT is entirely unnecessary with proper network configuration and management. You should really be doing it more as a hobbiest/enthusiast, or contributer since its open source. Here are some wikipedia links that explain some of the basic networking concepts I mentioned in more detail:

• Dynamic Host Control Protocol
• IPv4 and IPv6
• Subnet and subnet calculator

---
class EOSERV {
Programmer | Oldbie
Open source EO Client: https://github.com/ethanmoffat/EndlessClient
};

ethanmoffat posted: (30th Apr 2016, 07:00 am)

When I was in school, our university had a Class B public IP address space. They used public IPs for EVERYTHING and were constantly running out of addresses as more people connected more devices to WiFi. Terribly managed network, but it sounds like the same problem you're having.

The way it works with DHCP is that a device will send out DHCP request packets upon connecting to the network. If a DHCP server responds, it will give out the next available address to the device (if no server responds the device gets a 169.254.x.x address). However - when the device disconnects, that address is still reserved for the device based on the dhcp lease time, which is configurable on the server. It won't go back into the DHCP "pool" until it hits a timeout. Once the timeout is reached, the DHCP server will see if the device is still connected, and if it isn't, it will put the address back in the pool to be re-used by another device.

You have a couple of options to solve it:

1. Lower the lease time for DHCP leases - this will ensure that old addresses that are no longer in use are freed back into the DHCP pool sooner (this is the solution our university used)

2. Use a different private IP address space - if you're using a /24 you're limited to 254 addresses (excluding gateway/broadcast address for the subnet). Assuming you're on a 192.168.x.x address, you could change your subnet to a larger mask like /23 (510 addresses) or /22 (1022 address) and have more space available.

3. Use IPv6 - I know IPv4 is easier, but IPv6 exists for the larger address space. I explicitly disable it on my home network since I don't need it, but it was invented to solve exactly this problem of running out of addresses. You'll need to enable a 6to4 tunnel of some kind at your gateway if your network's public IP is IPv4, which it probably is, so this is the most pain-in-the-ass option you can go with.

Looking at the source code of DD-WRT is entirely unnecessary with proper network configuration and management. You should really be doing it more as a hobbiest/enthusiast, or contributer since its open source. Here are some wikipedia links that explain some of the basic networking concepts I mentioned in more detail:

• Dynamic Host Control Protocol
• IPv4 and IPv6
• Subnet and subnet calculator

Couldn't have asked for a better answer!  Sounds like lowering the lease time or utilizing ipv6 would be the best way in terms of a quick fix.  Kind of figured they configured the router wrong for the type of situation it'll be in.  Just wish i had the login page's password so i can fix these things on my own.  Guess i'll try and explain this to the boss!

Thanks for the answer! Nice to see some of you are still around eoserv.net.