What are the two modes of UDLD?

The two modes of UDLD (Unidirectional Link Detection) are Normal and Aggressive.

In Normal mode, UDLD actively sends out UDLD packets but only detects unidirectional links and disables the port after a certain number of failed packets are received. This mode is sufficient for most typical environments, where links are expected to operate bidirectionally and where the operator may not want to take immediate action in case of a unidirectional failure.

Aggressive mode, on the other hand, increases the level of detection and responsiveness. In this mode, UDLD will immediately disable the port when it detects that that the wavelength of communication (or the side established as the sender) is receiving packets unidirectionally. This is suitable for critical applications where unidirectional link failure might lead to severe disruptions or security issues, allowing for a quicker response to such problems.

This understanding of Normal and Aggressive modes showcases the flexibility of UDLD and how it can be configured based on network requirements and failure response protocols.