RouterOS 5.7 DHCP not working

RouterOS General
1

During the process of changing a lot of network configuration last weekend, I upgraded from RouterOS 5.6 to 5.7 on an RB1100. On Monday I discovered that DHCP had stopped working.

DHCP requests were being seen by the RB1100 interfaces (using Torch), and the RB1100 could see DHCP traffic on the network (it detected a rogue DHCP server we set up for testing using an alert), it wasn’t firewall rules, there was nothing that could sensibly explain why the RB1100 simply refused to respond to any of the requests with an offer.

After a further day of trying to figure out which of the the many network configuration changes made during the weekend could have possibly caused it, I’ve just downgraded back to 5.6 from 5.7 and DHCP has suddenly sprung back to life. Configuration has remained the same.

Has something changed in 5.7 that could possibly cause DHCP to break using an identical configuration? The only talk I’ve seen about DHCP changes have been to get ready to introduce DHCPv6 but that’s not until 5.8, and it can’t be completely broken - our rogue DHCP server was running on an SXT, also on 5.7 (albeit mips rather than ppc).

2

We’ve been seeing occasional DHCP server failures under 5.7 (x86) as well. We tried disabling and reenabling the VLANs, DHCP servers and IP addresses, with no success. Finally, I had to reboot a router (with a 14 day uptime) to reestablish DHCP service. When it booted up, the DHCP servers were red in WinBox, so they had to be disabled and reenabled once more, then they started working. The only other oddity that we noticed was that the CPU was hovering around 50% before the reboot then 2% after.

I have another router with a 12 hour uptime (upgraded to 5.7 last night) showing similar symptoms, but I can’t reboot it until our maintenance window tonight to see if that clears it up.

-Matthew

3

I’m glad somebody else has seen the same behaviour! I was beginning to think I was the only one.

For me, rebooting made no difference. It wasn’t until I downgraded that it suddenly sprung back to life.

4

problem will be fixed in 5.8