Hello Sathish
Yes, you’re correct. UDLD frames aren’t like BPDUs. UDLD is a Layer 2 protocol that works with the Layer 1 infrastructure to determine whether a link is bidirectional.
As for your question, yes, an alternate port can respond to and send UDLD frames. When UDLD is enabled on a port, the port transmits UDLD frames containing its device and port IDs to its neighboring device. These frames are echoed back to the port and if the port does not receive its own device and port IDs for a specific duration of time, the port can go into err-disable state or it can be considered as “undetermined”.
This mechanism helps in detecting unidirectional links to avoid loops in the network. It’s important to note that UDLD is not a replacement for STP, but a complementary technology.
I hope this has been helpful!
Laz