Tag: troubleshooting

Lessons learned and a case study on application slowness (brownout) troubleshooting for network management.

If you use Cisco VIRL to create virtual network models, here’s help with loading issues that occur when modeling multiple devices.

One of my customers asked for helping troubleshooting a port-channel between a HP-UX server and a Cisco Nexus 7000. I did not know much about HP-UX server configuration, but I [...]

I’d like to tell you a little story about something that came up recently when troubleshooting Wireless (WLAN) multicast (“IPmc”). I ran into something that was a bit unexpected … [...]

I noticed that you may not initially be able to set the clock time and date on Nexus 5Ks. For example: SWITCH-5K2# sh clock 18:16:56.460 UTC Fri Jun 12 2009 SWITCH-5K2# clock set 13:21:00 13 feb 2014 Setting clock from CLI is not allowed in this VDC. SWITCH-5K2# However, the…

I have been thinking about the interaction between LACP system IDs, port-channels on switch stacks, and virtual port-channels on Nexus gear. I saw some 'interesting' behaviour last week when helping a customer update the software on his 3850 stack. His stack was connected to a vPC port-channel on a pair…

One of my customers recently had an STP issue in his remote data center. He was not sure of all the details, but sometime during or after the migration of some Layer 2 links between his N7K and N5Ks into port-channels (possibly while VMware infrstructure changes were being made) his…

In the last week I talked to two different customers about issues with their port-channels, vPCs, and Spanning-Tree Protocol. The first customer thought he had a STP issue between his N7Ks and his N5Ks, but he actually had vPC design issue. The second customer also had the same design issue,…

I use multiple VPN clients, depending on which customer I am supporting on which day. I regularly use the Cisco VPN Client, the Cisco AnyConnect VPN Client, and the built-in Native Cisco VPN Support on my Mac (I'm currently running Snow Leopard version 10.6.8.) However, a recent customer project led…

The newer versions of NX-OS support 1G or 10G on the N5K, but the N5K is not auto-speed sensing. A mini case study follows.

In my last posts, Application Analysis Using TCP Retransmissions, Part 2, I described how application performance is impacted by TCP Retransmissions. Of course, there are many other causes of poor [...]

I was talking to some network engineers at an organization I will call Charlie. They thought they had a redundant network, but after looking at their network I believe it [...]