the worlds gone mad

Dual-active Detection (DAD) is designed to prevent a split-brain scenario where both VSS supervisors become active in the event of a VSL link failure. It uses a separate (from the VSL link) secondary communication link to communicate the devices state.
When the VSL link fails the standby switch becomes active and the current active switch is informed of this over the DAD links and goes into recovery mode to stop a split-brain situation occurring.

A recent project I was working on involved the need to join a new office to our existing Data Centres and OSPF core using a Gig circuit over the Internet. To flesh out this idea and test its viability I thought I would try and solve an ESX capacity problem I have at home by moving vCentre into the cloud.

Useful commands for managing VMs and vSwitches from ESX console. If the command has been executed successfully there will be no output returned to screen (no output = success!!!).

Intel NUCs only come with 1 built in NIC so when using them as ESX hosts it is useful to add additional USB ethernet adaptors. Before these will be recognised by the ESX OS the drivers need to be installed using a VIB file.

A cisco vswitch that can be used instead of the default VMware DvS to have a similar environment to that of Cisco physical NXOS switches. The control and packet communication can either be carried over VLANs in Layer2 mode or IP addresses in Layer3 mode. The default and Cisco recommended solution is L3 mode.

Local and Distributed vSwitches server the same purpose as physical switches allowing for VM vNICs to be assigned to specific VLANs. In a production environment it is usual to define a local vSwitch on each ESX host for management and backdoor and have distributed vSwitches shared between hosts for VMs.

Ever thought about how ACS gets an end users IP or how when showing an interfaces authentication sessions it had the IP of the host attached? This all stems from IP Device Tracking. I only recently came across it when troubleshooting an issue we had with windows machines not getting a DHCP address due collision detection involving the 0.0.0.0 address. Although there are lots of posts about people having a similar issue and the workarounds, I couldn’t find much information on the exact reason why this happened. This post is designed to give more reasoning on why this happens.