Question re AC68U IP generation from MAC address

[OttoL]

Hi all, relative noob here. I couldn't find an answer to the question at hand in the forums so if this has been mentioned somewhere in another thread I apologise.

Recently I noticed that my internet speed was around 1/5 of what I was paying for (1Gb over glass fiber). I checked the speed before my router (AC68U, which has been working fine for years) and the speed was fine there so it was the router. Of note, I've been using the Merlin firmware for years, mainly to allow install of Skynet and Diversion. After quite a bit of searching I decided to do a factory reset (first one in years after numerous firmware updates), which did bring my speed after the router to more reasonable values (50-75% of max) even though it could still be better.

ANYWAY, to come to my question. I had to reconfigure a few things after the reset (e.g. re-establish the WIFI SSID etc, re-initiate Skynet & Diversion), a bit annoying but OK. What struck me though is the following. I have some 15 IoT dimmers, lights and switches connected via WiFi. Strangely all of these had received different DHCP IP addresses from before the reset. I was under the impression that the DHCP-attributed IP was calculated by the ASUS based on the MAC of connected devices, so how can that be? A number of devices which I had given a fixed IP address via the router äddresses around the DHCP pool) still had their old IP attributed by DHCP even though they did not show up in the list of fixed DHCP addresses anymore... so e.g. my VOIP box, satellite and TV still had their old IP's (and no, there is no static address configured in those devices).

How come all IoT things got different addresses now?? This is mildly annoying as I have to update all their web interface addresses and also in my yet quite small Home Assistant setup they all have to be reconfigured. If I have to do this everytime my router acts up that could be very annoying especially with multiple home/light/alarm scripts and automations running based on ip addresses...

Thanks in advance for any comments or help!
Maarten

 

[Adooni]

why you will not assign DHCP manually for each device?
LAN- DHCP SERVER - Manually Assigned IP around the DHCP list

AC68U is to week for 1Gb especially if you have XX devices and router need to work as software switch, wi-fi etc. do not even turn on QoS as for 1Gb u do not need it and even with adaptive QoS speed for this router will be below 500Mb
If you want to stay with ASUS you should consider AX86U as upgrade.

 

[OttoL]

Thanks Adooni for your quick answer. I fully understand I can attribute DHCP manually for each device, and probably I will end up doing that. Indeed that is what I did for the devices I mentioned above, and they retained the same IP even after the factory reset - even though they don't show up anymore in the "manually assigned IP" list (?).
My question was more - why, after a factory reset, does the ASUS DHCP not calculate the same IP-adresses as before from the MAC of each device... as I understand (maybe wrongly) it should do that unless you manually attribute a different IP?

Thanks for the upgrade tip BTW, maybe I'm stretching the poor old AC68 to its limits...

 

[Adooni]

factory reset clear nvram - there is no any information left to start from. Asus do not have any info saved. If you doing it for same testing you can save those settings.
Auto DHCP is providing IP no. looking at what device they 1st recognize - I could be wrong here as for more then 20y I am working with routers, servers, net etc I never used Auto DHCP and always assign it manually for "important devices" (rest I do not care ).

 

[ColinTaylor]

My question was more - why, after a factory reset, does the ASUS DHCP not calculate the same IP-adresses as before from the MAC of each device... as I understand (maybe wrongly) it should do that unless you manually attribute a different IP?

IP addresses are generated pseudo-randomly based on a hash of the client's MAC address and the available address range. So if you change the DHCP IP address range the generated addresses will be different. For example, a DHCP range of 30-254 will generate different addresses than 2-254.

Also, bear in mind that some devices (like Windows PCs) will remember what IP address they previously had and ask for the same address again. If that address is free and not reserved it will get that address.

 

[OttoL]

Hello Colin, that makes perfect sense. I think I set the dhcp range to start at .1.3 instead of .1.2 before the reset so that explains things perfectly, and indeed my linux satellite box, the voip box and the android TV may have "remembered" their last attributed IP and requested it again. Mystery solved (it seems), thanks very much!