UDLD Loop issue?

[kmand1234]

Our department lan is a collection of HP switches, one of which is connected by 10G fiber to a Cisco switch that 

is our gateway to the campus network. Today the Cisco switch shut down our with the UDLD loop error below.

This has been working for many months, so I'm trying to understand the sudden error. Does it represent an issue on that

fiber connection itself, or something further back on our lan (or the campus backbone)

2015 Jun 22 12:38:29 400DowDr1A-m2 %UDLD-4-UDLD_PORT_DISABLED: UDLD disabled interface Ethernet1/5, transmit/receive loop detected

2015 Jun 22 12:38:29 400DowDr1A-m2 %ETHPORT-5-IF_DOWN_ERROR_DISABLED: Interface Ethernet1/5 is down (Error disabled. Reason:UDLD Tx-Rx Loop)

[InayathUlla Sharieff]

Hi,

This because that the UDLD Protocol disabled an interface because it detected connections between neighbors that were functioning only in one direction, which might potentially cause spanning-tree loops or interfere with connectivity. The cause is likely to be hardware related, either due to a bad port, a bad cable, or a misconfigured cable.

You might be running UDLD aggressive mode.  It basically polls a fiber link for connectivity in both directions, and when your switch detects uni-directional traffic on a fiber link, it will shut the port down (err-disable) to avoid a loop developing.  I'd check the fiber or the fiber modules on both ends to make sure there's no issues.  Here's more info on the UDLD feature:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.1_19_ea1/configuration/guide/swudld.html

HTH

Regards

Inayath

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