DHCP Client Retry Interval

RouterOS General
1

Charter Cable Internet Service (in United States), and perhaps other Internet providers, sets their modems so that if you request a DHCP address too many times, your MAC Address is blacklisted UNTIL you do not request an address for at least 3 minutes.

This causes a problem with Mikrotik, because if your mac address gets blocked, the Mikrotik will keep searching over and over and you will NEVER get an address because you keep resetting the 3 minute timeout required to reset the dhcp block.

It’s not difficult to get blocked. When the modem and router are powered on together (like after a power outage), it sometimes gets an address in time, and it sometimes has to retry a few times to get an address, and then it gets blocked. (Or after an ISP outage).

To fix, you then have to unplug the miktotik for 3 minutes, then it gets an address fine… or you can change your mac address and immediately get a new address without waiting 3 minutes.

I have found that if I release/renew 2 times within 1 minute (on purpose for testing purposes), my mac address is blocked for 3 minutes.

The purpose of this block is to prevent dos attack on the isp dhcp server, but they set the threshold VERY low.

So, we need a way to make the mikrotik dhcp client to only retry every 4 minutes, instead of being so aggressive.

2

it is not aggressive, it performs DHCP auto-configuration sequence as it is described in RFC.

you can create scheduler that start on startup with some delay, that will enable dhcp-client a bit later. That way you will ensure that router waits long enough and it gets IP address every time.

something like:

/ip dhcp-client disable [find]
:delay 30
/ip dhcp-client enable [find]

that is, if you have one dhcp-client on the router, if you have several, you can add where interface= to the find clause.