Could you explain de differences between UDLD and spanning-tree loop guard, it seem to be very similar and use for the same purpose. Maybe I'm missing something here - but when I plug two switches together with a duplex fiber cable and simulate a "cut" single fiber buy pulling one of the two fibers out of the GBIC the links goes down. Like your first picture in the post. Hi Gadget, but isn't device able to detect that no cable is inserted? You may need to cut the cable to get the effect, possibly.
One fiber for Tx and one fiber for Rx. Unplugging and maybe not is just the same as taking the single fiber and cutting it - no more light source. Am I still wrong on this? Generally speaking, if they are placing a Cisco ME series Ethernet switch at your site, you'll probably have problems passing UDLD to your remote side.
If they are using true transport gear Adtran, Ciena, Adva, etc its at least possible. Again, this very much depends on how your service provider delivers the circuit. It does nothing to protect against loops; only that the physical layer is functioning as expected between two connected nodes. Their other boxes might do it as well, but I don't run them so I can't provide much insight.
Current configuration allows changing the interval and timers very similar to BFD as low as ms to discover failures. All vendors of course recommend to not run udld across links to other vendors equipment, but i have only seen it trigger an errdisable event at one site.
And it only brought down 1 of the 2 uplinks from the access switch to the distribution layer casuing spanning tree to failover to the alternate link. Disabled udld on the Cisco port and all was well. Any ideas? Hello, how did you simulate the udld configured port to stop transmitting hello's?
In which case, our company is choosing BFD as a pref for link failure detections. Obviously it does depend on Layer 1 also, even though it is a Layer 2 protocol. UDLD functions on a per physical port basis i. Hence the best practices recommend to use them both.
Useful article. This behavior does not depend on the UDLD mode. This is noteworthy because many articles on cisco. You have to set both sides of the link to speed no negotiate in order to lab a uni-directional link event. Once you set this you can pull one of the fiber strands out and see ULDD in action. Could you explain this sentence please?
Have you been looking for a better way to model your network infrastructure? Check out what we're doing with NetBox! Open source and widely extensible, NetBox has enabled thousands of organizations to automate their networks like never before possible. Take the network bellow as an example, where the link from A to D goes unidirectional. In the below example we have three interconnected switches with an extra redundant link.
The same unidirectional link suddenly arrises as outlined in step 2 above. This loop, which would have otherwise gone undetected by STP, has been identified and mitigated. Configuring Spanning Tree on Meraki Switches. The Meraki implementation is fully inter-operable with the one implemented in traditional Cisco switches. However, there are a few differences that should be noted:. UDLD helps to prevent forwarding loops and blackholing of traffic by identifying and acting on logical one-way links that would otherwise go undetected.
Configuring UDLD on a trunk group's primary port enables the feature on that port only. Dynamic trunking is not supported. After you create the trunk group, you can re-add the UDLD configuration. Consult the release notes and current manuals for required software versions. If the incoming port itself is already blocked on the VLAN it will be dropped right away, and no re-forwarding will be done. Uni-directional link detection UDLD.
Configuring UDLD. Configuring transceivers and modules that have not been inserted. Uplink failure detection.
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