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UDLD feature on L2

Dear Sir/Madam

Our customer request us to deploy the UDLD feature on their L2 spanning tree network. So I tried to read some UDLD documents and did some testing. By Cisco UDLD documents description, the UDLD can perform with L1 autonegotiation feature to overcome two issues. The two issues are that Link is up on both sides, however, packet are only received by one side and Wiring mistakes when receive and transmit fibers are not connected to the same port on the remote side. So I tried five testing about the physical layer testing. But I cannot simulate the above two issues. Do you have any ideas about UDLD? What siutations we need to deploy it? Please find my testing cases as following. Thanks!

Case1: Switch A and Switch B GE port are configured with autonegotiation when I put out the transmit side of switch A or receive side of Switch B, both Switch A and Switch B GE port will be in DOWN state at once.

When I put out the transmit side of Switch B or receive side of Switch A, both Switch A and Switch B GE port will be in DOWN state at once.

Case2 Switch A(Auto negotiation) while Switch B (no auto) Switch A GE DOWN but Switch B GE UP (not yet disconnect fibre)

Case3 Switch A and Switch B are no auto negotiation When I put out the transmit side of Switch A or receive side of Switch B, Switch A GE still up but Switch B GE in DOWN state at once.

When I put out the transmit side of Switch B or receive side of Switch A, Switch B GE still up but Switch A GE in DOWN state at once.

Case4 Switch A transit to Switch B receive and Switch A receive to Switch C transmit (all A.B.C are in auto negoitation). All ports are in DOWN state

Case5 As same as Case4 but all the Switch A, B and C in non autonegotiation. Switch A and Switch B UP but Switch C is DOWN.

Joseph Lee

1 REPLY
Anonymous
N/A

Re: UDLD feature on L2

UDLD is a Layer 2 protocol that works with the Layer 1 mechanisms to determine the physical status of a link. When you enable both autonegotiation and UDLD, Layer 1 and Layer 2 detections work together to prevent physical and logical unidirectional connections and the malfunctioning of other protocols. UDLD works by exchanging protocol packets between the neighboring devices. In order for UDLD to work, both devices on the link must support UDLD and have it enabled on respective ports. Each switch port configured for UDLD will send UDLD protocol packets containing the port's own device/port ID, and the neighbor's device/port IDs seen by UDLD on that port. Neighboring ports should see their own device/port ID (echo) in the packets received from the other side. If the port does not see its own device/port ID in the incoming UDLD packets for a specific duration of time, the link is considered unidirectional. The following document gives you more ideas:

http://www.cisco.com/warp/public/473/77.html

(See the last paragraph for more references)

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