have you discarded STP/RSTP issues? which version of SwOS are you using?
is OLD RB260GS which supports only up to SwOS 1.7 or the later version RB260GS(CSS106-5G-1S) which supports up to SwOS 2.13 ?
recent one RB260GS(CSS106-5G-1S) which supports up to SwOS 2.13
Issue Resolved:
From Support:
It is related to RSTP. The RB450Gx4 with HW offloaded bridge and configured VLANs on the switch menus tags RSTP BPDUs from CSS106. These tagged BPDUs are received on the CPU and they should be ignored based on the IEEE standard. Since RouterOS 7.3 we have made a software fix that ignores such packets. So after upgrade to 7.3, these two devices always tries and fails to negotiate the root bridge and cause DHCP related problems.
The related changelog entry:
*) bridge - ignore VLAN tagged BPDU;
The problem is that switch chip on RB450Gx4 does not correctly treat the BPDUs. We will try to improve this in future releases, but I cannot provide a release date.
Some possible workarounds:
1. Disable RSTP on RB450Gx4 (/interface bridge set protocol-mode=none) or CSS106.
2. Configure a switch rule to redirect the BPDUs to the CPU, for example:
/interface ethernet switch rule
add dst-mac-address=01:80:C2:00:00:00/FF:FF:FF:FF:FF:FF ports=AP1,RBSSwitchConnectedPort,UnifiAP redirect-to-cpu=yes switch=RBGX4Switch