please explain udld in detail

On 14.05.2007 19:22 cheeku wrote

What is unclear?

UDLD is a Layer 2 protocol that works with Layer 1 mechanisms to determine the physical status of a link. At Layer 1, autonegotiation takes care of physical signaling and fault detection. UDLD performs tasks that autonegotiation cannot perform, such as detecting the identities of neighbors and shutting down misconnected ports. When you enable both autonegotiation and UDLD, Layer 1 and 2 detections work together to prevent physical and logical unidirectional connections and the malfunctioning of other protocols.

Arnold

Maybe it's the purpose that is not clear?

In the case of a 10M or 100M UTP ethernet (10BaseT or 100BaseT), link when you connect two devices each will display a green light indicating that the link is "up".

Lets call the two devices A and B.

The problem occurs when for example the cable is faulty and the signal path from A to B is interrupted but the path from B to A is not. B will correctly show "link down" but A will show "Link up".

This can cause dissruptive network failures since some upper layer protocols were not designed to operate correctly under these curcumstances. e.g. Spanning Tree, RIP.

OSPF, BGP for example do detect this type of failure and are not affected.

Gigabit Ethernet had the functionallity of UDLD built in (to layer 1) and so it is not necessary or applicable for GBE.

thank you....!!!!!!