Thursday, 3 May 2018   9 min read

Link-state advertisements (LSA) are used to communicates the router’s local routing topology to all other local routers in the same OSPF area. There are 11 types of LSAs although only the 6 most commonly used ones are described in this post.

Cisco Express Forwarding (CEF)

Sunday, 22 April 2018   14 min read

I am currently studying to rectify my CCIE and it is at these times that I realise there is so much I have studied and learnt but forgotten. There are many cool things I come across that I think at the time are useful features that I need to remember, but unfortunately if you don’t have a real world use for them they are soon put to the back of the brain and over time forgotten. The same applies with taking for granted the way things work, be that ARP, DHCP or the process a switch or router goes through when moving traffic. I came across some of my old notes on CEF which I thought worth sharing.

VSS Recovery mode

Thursday, 22 March 2018   6 min read

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.

Checkpoint Identity Awareness

Saturday, 13 January 2018   7 min read

The 3 main elements that run identity awareness under the hub are Active Directory Query (ADQ), PDP and PEP. They all intertwine in some way to allow the different blades of the Checkpoint to track and restrict access based on AD user and machine name. I tested these features as part of a POC and personally I would not consider them fit for purpose in a production environment. See the caveats at the end of the post for more details on this.

Deleting Checkpoint Logs

Saturday, 13 January 2018   1 min read

The directories that need to be emptied to delete all the logs on the Checkpoint managers.