Why do I have to reboot my modem to connect a new router?

2

Sometimes, not all the time, when I change my router, I have to reboot the modem before the router can detect the WAN connection.

This does not make sense to me. Why does it seem like the modem is discriminating who it's sending data to.

Some sites suggests that it could be a conflict between the LAN IP address of the modem and the router, but that never really happens. The modem and router usually default to different IP ranges (ie. 192.168.100.1 vs 192.168.1.1)

Others suggest that it's because the modem stores the MAC address of the last router, and won't forget it until it is reset.

What's the deal with this? Why are modems designed to be like this? Are there ways around this other than a reset?

vinhboy

Posted 2015-05-31T20:34:42.863

Reputation: 321

1May be, The modem default is to clone a the LAN Client MAC. Try to check that. – user.dz – 2015-05-31T20:49:06.823

Answers

2

Most modems have a hidden DHCP server built in. This can be seen on a hidden administrative webpage, if you know how to access it. Your router is getting its external IP through DHCP from the modem. Since these home modems have one device attached to them - the router - it stores the router's MAC. If you were to attach another device, which would have a different MAC, it wont communicate with the new device until it is reset with a reboot, or by using the hidden administrative page. This is a security feature which prevents people from disconnecting your router and putting something else on/in the network

Now I am curious, why do you have to replace your router every few years?

Keltari

Posted 2015-05-31T20:34:42.863

Reputation: 57 019

Forget the why. Ask for how many such replacements the OP has been keeping track of this specifically in order to be able to state the question... – a CVn – 2015-05-31T20:52:47.270

@MichaelKjörling about 4 times in the last 2 years on my own modem. I've had the unfortunate task of replacing 2 routers which were lemons, and the other two time was just me testing out stuff. I also help other people with their network, and this is just something I noticed over the years. It's just an annoyance that I want to understand better. Ps. I am updating my questions so you don't think I am one of those crazy network people who upgrade their router every few months... haha. I generally don't. – vinhboy – 2015-05-31T21:09:29.437

Asked: 2015-05-31T20:34:42.863

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Active: 2015-05-31T21:45:54.763