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chupkb
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Joined: Sat May 26, 2018 12:41 pm

CSS326 and loopback protocol (CTP)

Sat May 26, 2018 1:27 pm

Hello everyone.

Is there any information about loopback protocol (ethertype 0x9000), aka configuration test protocol implementation in SwOS? I did not find anything about this in the documentation.

The problem is next.

I just replaced several my Cisco switches with Mikrotik ones and I have an issue with two my provider uplinks.

Two different providers are connected to the switch by the 802.1Q trunk. Every connection have several tagged VLANs. All of them are coming to the router-on-stick and next to the branches. But, when I connect both providers in one Mikrotik switch simultaneously, traffic from/to any provider VLAN is partically lost. Losses are about 10-70% frames, depends on bandwidth utilization. When I shut one of that uplinks (any) down, other uplink makes 100% reliable, no one frame is lost in this case.

I have solved this issue after sniffing incoming traffic. Provider A has an Cisco device on it's side, provider B has an D-Link device. So, Cisco device sends keepalives, function 1 of loopback protocol, and D-Link device uses it's own implementation of CTP called loopback detect (function 256). It seems that Mikrotik reacts on that service frames and makes it's ports err-disabled without any notification.
In my case, I just asked both providers to disable keepalives and loopback detection. My problem is gone, but investigation was quite hard. Please, make some record about loopback (CTP, ethertype 0x9000) in your documentation.

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