What are Keepalive Messages on a Cisco Switch?

Question

Computer networks

ISP->media converter->switch
The interface towards the provider falls into errdisable:
%PM-4-ERR_DISABLE: loopback error detected on Gi0/2, putting Gi0/2 in err-disable state.
The problem is that the keepalive of the switch itself comes back, so it locks the port, as soon as I do [no keepalive] on the interface, the problem goes away (the channel is normal, there is no flood, there is no IPS loopback)
Here is what Cisco writes:
A loopback error occurs when the keepalive packet is looped back to the port that sent the keepalive. The switch sends keepalives out all the interfaces by default. A device can loop the packets back to the source interface, which usually occurs because there is a logical loop in the network
Everything is fine and understandable, but what is this keepalive frame in this case and what is meant by logical loop (this is not an L2 loop)

Answer 1

keepalive is a multicast frame that is sent by the switch, and if the switch receives such a frame with its mac address as the sender, it is considered that a loop has formed. In this context, the logical loop is exactly the L2 loop.
Maybe the provider has something, maybe the tsiska itself with the port. show errdisable recovery what does it say?
Have you tried changing the port on the switch?

Answer 2

Enable "no keepalive" on the interface.
This has nothing to do with stp and with loops too - it's just a problem in the compatibility of the medic and the tsiska. It happens

Answer 3

Keep-alive mechanisms
Ethernet interfaces
On broadcast media such as Ethernet, the keep-alive mechanisms are somewhat unique. Because the number of possible neighbors on an Ethernet is large, keepalive messages do not provide for determining the availability of a cable path to any particular neighbor. These messages only test whether the local system has read/write access to the Ethernet cable. The router creates an Ethernet packet that contains the source and destination MAC address of the router itself and a special Ethernet code of 0x9000. The Ethernet equipment sends this packet over the Ethernet cable and then immediately receives this packet back. This checks the transmit and receive hardware in the Ethernet adapter, as well as checking the integrity of the cable.