static DHCP

[VirtualLarry]

When setting up static DHCP in a router, do you select IP addresses that are outside the DHCP server's range, or do you select IPs inside that range, and the DHCP server is smart enough not to hand out the reserved IPs to random clients?

 

[Engineer]

Originally posted by: VirtualLarry
When setting up static DHCP in a router, do you select IP addresses that are outside the DHCP server's range, or do you select IPs inside that range, and the DHCP server is smart enough not to hand out the reserved IPs to random clients?

That's a good question. I read in the last few days (don't remember where) that it's best not to place the static DHCP in the dynamic pool so it would "probably" be better to not have them overlapping.

 

[Fardringle]

If you assign an address that is within the normal DHCP pool, it's possible that the DHCP server could give the same address to another system on the network, causing an IP conflict.

 

[JackMDS]

It depends on the Entry Level Router.

In Some Routers you can only assign within the DHCP range.

In some Routers when you assign within the DHCP range and the computer that supposes to get the IP is Off, another computer might grab it.

In many Routers assigning Static DHCP within the range works OK and nothing is Grabbed since the assignment is attached to the MAC number.

In sum live is full mysteries, find out which is yours.

 

[Engineer]

Originally posted by: Fardringle
If you assign an address that is within the normal DHCP pool, it's possible that the DHCP server could give the same address to another system on the network, causing an IP conflict.

One would think that assigning a "Static DHCP" entry "in the router" would result in the router being smart enough to not give out that particular IP except to the PC associated with the entered MAC address. Like Jack pointed out though, you never know what you're going to get with home routers/3rd party firmwares/etc. until you try.

If you keep it outside the range of the dynamic pool, you will know exactly what you should get (well, most of the time! )

 

[VirtualLarry]

While we're on the subject of DHCP, can someone tell me if this is a bug?

I recently (just an hour ago) set up a Trendnet 652 wireless-N router here at a friend's house, replacing their existing wired router setup.

It performs well, and now they are hitting 27Mbit/sec on speed tests, rather than 5.

But when I was setting it up, it defaulted to a LAN IP of 192.168.10.1. One of the computers that was connected to it was powered up, and pulled an IP of 192.168.10.101.
I had to change the LAN IP of the router to 192.168.0.1, but I didn't reboot the router. I rebooted that machine that had the 192.168.10.101 address, and when it came back up, it pulled the same IP from the router. Even though the current router config shows that the DHCP pool is 192.168.0.100-192.168.0.150. The router didn't clear it's DHCP leases when I switched its IP around. So I had to power down the PC, and then power-cycle the router, and then all was well.

 

[mcmilljb]

Originally posted by: VirtualLarry
While we're on the subject of DHCP, can someone tell me if this is a bug?

I recently (just an hour ago) set up a Trendnet 652 wireless-N router here at a friend's house, replacing their existing wired router setup.

It performs well, and now they are hitting 27Mbit/sec on speed tests, rather than 5.

But when I was setting it up, it defaulted to a LAN IP of 192.168.10.1. One of the computers that was connected to it was powered up, and pulled an IP of 192.168.10.101.
I had to change the LAN IP of the router to 192.168.0.1, but I didn't reboot the router. I rebooted that machine that had the 192.168.10.101 address, and when it came back up, it pulled the same IP from the router. Even though the current router config shows that the DHCP pool is 192.168.0.100-192.168.0.150. The router didn't clear it's DHCP leases when I switched its IP around. So I had to power down the PC, and then power-cycle the router, and then all was well.

Both the computer and the dhcp server hold onto the lease. The computer was probably holding the lease which it had before you switched the router's dhcp server settings. When you changed the settings on the router, it probably cleared all its dynamic leases, but it doesn't notify the computer. You should have been able to issue a dhcp release on the computer which drops the lease and notifies the dhcp server that it's releasing the lease. Then you could have issued a renew dhcp command to request a new lease. If it still received the wrong address, the router probably needed a restart to activate the new settings.

 

[spidey07]

Originally posted by: VirtualLarry
While we're on the subject of DHCP, can someone tell me if this is a bug?

I recently (just an hour ago) set up a Trendnet 652 wireless-N router here at a friend's house, replacing their existing wired router setup.

It performs well, and now they are hitting 27Mbit/sec on speed tests, rather than 5.

But when I was setting it up, it defaulted to a LAN IP of 192.168.10.1. One of the computers that was connected to it was powered up, and pulled an IP of 192.168.10.101.
I had to change the LAN IP of the router to 192.168.0.1, but I didn't reboot the router. I rebooted that machine that had the 192.168.10.101 address, and when it came back up, it pulled the same IP from the router. Even though the current router config shows that the DHCP pool is 192.168.0.100-192.168.0.150. The router didn't clear it's DHCP leases when I switched its IP around. So I had to power down the PC, and then power-cycle the router, and then all was well.

You didn't follow the rule of home networking.

1) Turn everything off
2) Bring up router
3) Wait 60-120 seconds
4) Turn on clients

You can't just go change things willy-nilly without rebooting in the SOHO world.