@malada DHCP

 

@malada 

 

One problem with setting a device to a specific IP address is if that address could be given out by DHCP server.

 

Depending on router s/w, it, the router, might be aware of what IP Address are in use and not hand out a duplicate. All routers know what they handed out, but may not know if a device asks for a specific IP Address. Even if it did, there is alway the chance that since the IP Address is NOT reserved on the router, it would hand it out to a device and then when the device with the fixed address connects, it would honor that request and that would in turn disconnect another device that had that IP address.

 

I avoid this by setting the IP address that the device has fixed in the Reserved pool and it is my responsibility not to use that Reserved IP Address, Problem solved.

 

However, as I said, if the router f/w is smart enough to not hand out an IP address that was used before, either would work.

@IrvSp That wasn't actually my questions but you must have some telepathic abilities because I googled for exactly what you mentioned. So far I always set static IPs on the devices but I have some devices that I need to put on static IPs but they don't have such an option. That's how I found address reservation and I started wondering which one is better. My googling and your respond come to the same conclusion, use address reservation. Besides what you said, people also like the fact that it allows them to control all devices from one point, the router which also allows configuring things remotely. Plus I really like the fact that I can give all these "unknown" devices names.

 

As for my actual question, when you add an address reservation entry you have to choose an IP address. As of now my DHCP range is 1-155 and my static range is 156-254. So my question was if I need to chose a number in the DHCP range or the static range. Since address reservation is handled by the DHCP server I figured it would be in the DHCP range but some people say it should be in the static range. This might be router dependent so I asked on this forum. There was another response and that person said that it should be in the DHCP range.

 

malada wrote

There was another response and that person said that it should be in the DHCP range.

@malada 

 

Well, in some routers you might be able to 'mix' them, other maybe not?

 

If the DHCP Server 'knows' ALL the IP Addresses in use, either fixed or it handed out, it will work. If it only knows of the ones it hands out, you could have a collision. An 'old' router (from many years ago) I had collisions happen and the fix was simple, reduce the DHCP Pool and make all fixed (and reserved) IP Addresses outside the DHCP pool.

I use Address Reservation because I port forward my cameras so they can be viewed from anywhere in the world I can get a WIFI signal. When I assigned my DVR MAC address, I used an address that was not currently in use by any device by the router (in my case I used 192.168.0.119 which is well within the DHCP range). As a practice, I will reboot my router after making any router changes. I can see where a reboot may be required if you were able to assign an address that was in use by another device. I have more than 19 devices and have not had any collision.

@ArcherC8 

 

Yes, some router's what you've done could be correct.

 

I always only use for some devices a 'known' IP address. To avoid any collisions I carve out of the DHCP pool a block a IP Address I can 'manage'. For instance I start the DHCP pool @ 192.169.0.101.

 

That leaves me 99 IP Address to either Reserve on the router or set in the device settings. My responsibility is not to give the same IP address to 2 device.

Problem solved.

@IrvSp You said "To avoid any collisions I carve out of the DHCP pool a block a IP Address I can 'manage'". So basically you are using what I call the 'static IP address block'. Now I am getting confused, though. So you are using an address outside of the DHCP block. @ArcherC8  says that I should use an address in the DHCP block. And if I actually let the router decide then it selects something in the DHCP block.

 

The reason the router selects an address from the DHCP block might be because it doesn't have control over addresses used outside of the DHCP block. So maybe it really doesn't matter what address I am using (inside or outside the DHCP block). When the router sees a new MAC address (or a MAC address whose lease time expired) then it will first check the Address Reservation table. If the MAC address can be found it will assign it the set IP address. If it's in the DHCP block then the router will make sure it will not assign another device the same IP address. If the IP address is outside of the DHCP block, the router will still asign it the given IP address but then it's all my responsibility to make sure there is no conflict. Actually, as I write this I think that kind of makes sense but of course I don't know if that is what my router (Archer C3150) is doing.

 

malada wrote

If the MAC address can be found it will assign it the set IP address. If it's in the DHCP block then the router will make sure it will not assign another device the same IP address.

@malada 

 

Yes, this is correct. However, there is an 'order' of who asks for an IP address first.

 

Look at it another way. You have an IP Address 192.168.0.10 assigned to PC#3. The DHCP pool is left at default starting at 192.168.0.2. PC#3 is not powered on. You turn on PC#1 and #2. You also have some IoT's connecting as the router either starts or they come on. Some device gets assigned 192.168.0.10 by the DHCP server. What happens is when PC#3 tries to connect it will force off (do to an IP Address collision) whatever device was on that IP Address. This is for the case where the IP Address is set in the device, not on the router by MAC Address.

 

Now routers do usually track what IP Addresses are handed out that are in the DHCP pool, and if PC#3 came on first, more than likely it would know not to give that address out. I had an old Netgear that would though. It might also (the router) be aware of any Reserved IP Address it has and will not use those for the DHCP pool...

 

Again, creating a block for Static/Reserved/Fixed IP Addresses outside on the DHCP block that you manage is foolproof (as long as you don't assign the same IP Address to 2 devices).

 

Check this link out, https://superuser.com/questions/107302/does-a-router-know-not-to-hand-out-static-ip-addresses-to-other-devices

 

Bottom line though, do it which ever way you wish. As long as there is no collisions, you are good.

 

Me, I use Reserved for the PC's so I can easily transfer files or run programs on the PC's on the LAN from another one. I use IP Addresses that end in 0X0 but I could also used the NET NAME. Old school I guess?

 

@IrvSp Ok, so the first scenario is assigning a static IP address on the device and that IP address is within the DHCP pool. That of course will cause problems sooner or later.

 

The second scenariois also a user error. It assumes that computer #3 has a static IP in the DHCP pool. If the router is smart it tries to avoid the problem but that problem realy was caused by the user.

 

My question really is if I can use an IP address that is outside of the DHCP pool and at this point there is only one person that answered this and that answer indicates it says should be in the DHCP pool. Ther outer also chooses an IP in the DHCP pool. But as outlines in my previous post, I understand why the router might do that. My preference is that I use IP addresses outside of the DHCP pool but I don't know how the Tp-Link firmware work so maybe thers is something that makes this blow up.

 

malada wrote

 

My question really is if I can use an IP address that is outside of the DHCP pool

@malada 

 

My answer is YES, and to be absolutely sure there would be no collisions of IP Addresses (unless you assigned 2 devices the same IP Address) the only way to do it.