the worlds gone mad

we've lost the hope we had

Posted on 22 March 2018   6 min read

VSS Recovery mode

vss recovery mode scenario

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.

Posted on 21 July 2017   15 min read

Cisco N1000v Switches

cisco distributed vSwitches

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.

Posted on 14 July 2017   11 min read

Cisco IP Device Tracking

IPDT and DHCP collision detection

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.
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