DNS Changed and Lease Stopped Locally

RouterOS Wireless Networking
1

Hello!

I’m having a lot of RB433 boards and a ‘few’ of them are giving me a lot of those messages:

dns changed
dns changed
dhcp-client on bridge1 got IP address xxx
wlan1 link down
dhcp-client on bridge1 lost IP address xxx - lease stopped locally

And the devices are offline for a few seconds to minutes.
Can anyone give me an explanation how this can happen or what could be the reason for this?
The devices are not touched, etc so the link should not go down…

Thank you!

2

Hi, I came upon this exact problem, it ended up being the upstream DHCP server. Upon a DHCP “renew” request, the upstream server was returning the assigned IP address only, the server did not return additional information such as subnet mask etc.

This ended up being a known bug in Cisco’s DHCP proxy service on there ASR9K running ios-xr4.3.4

As the DHCPACK was not “correct” according to the Mikrotik, the router would go through a full rebind, which causes the interface to completely loose its current IP address etc, which then causes routes to dis-appear which then causes TCP connections to die (due to the router sending icml unreachable messages…)

I tried a Cisco 887 instead of the Mikrotik, when I was experiencing this problem, this is the log entry i was getting:

*Apr 14 00:26:33.732: DHCP: Lease Seconds: 600
*Apr 14 00:26:33.732: DHCP: Server ID Option: 203.94.52.1
*Apr 14 00:26:33.732: DHCP: ack received without mandatory subnet mask.
Please contact the DHCP server administrator to upgrade the DHCP server.
*Apr 14 00:26:44.720: DHCP: Client socket is closed
*Apr 14 00:28:25.720: DHCP: Client socket is opened

I also found that cheap modems did not have any issue.

I would try and capture the DHCPACK pkt, and confirm that all the fields are correct.

cheers

3

I have this same problem but the DHCP server is another Mikrotik device. I switch to static IP and it’s still happening but just link goes down. So anyone with this issue it could just be an underlying problem with the ethernet connection. I’ve changed to another port on the switch so will see if it persists