MST

So tonight I watched a video on MST.  MST is one of those things that has caused me headaches and watching Marko M. from iPexpert, it sounds like it is a headache from everyone.  It is can be very simple and very complex. 

I knew that VLANs mapped to instances.  I knew that it reduced the amount of instances per switch to reduce the amount of traffic/BPDUs going over a link.  I didn't realize some of the behind the scenes junk.

For example, I didn't realize that MST didn't take effect until you exited its config mode.  Good to know.  I can see that biting me in the behind when I configuring it and checking my config with do show commands.

I also didn't realize that VLANs can be mapped that aren't even created.  I never really thought about it.  Allows for future growth and it is already configured when the VLAN is configured and set up.  This is more of a planning and design aspect but still good to know.

Also found out how instance and VLAN mappings are shared.  This comes from the MST CONFIG DIGEST within the BPDU.  This is a hash that will match from switch to switch if they are mapped the same way.  The revision number and region name have no sway in the hash what so ever.  This makes me thing of a good diagnostic question or part of a question for the v5 test.

Finally comes the MSTI, CST, and IST.  I either didn't know about them all or forgot about them.  Good to see how they all fit together.  CST is used to connect to another STP mode (PVST or Rapid PVST).  IST is used inside the MST and MSTI is an instance of MST that uses IST to traverse essentially.  Because of the CST that connects a region to another mode, it makes the region look like one switch.  Again, a cool concept. 

Can't wait to try this in my lab again.  And speaking of that, there will be some labbing but not a lot until INE and iPexpert release more labs.  I do have the Cisco Press v5 Configuration Prep book.  May do a little but also thinking of watching videos and also knocking out my Brocade Certified Network Engineer (BNCE) real quick and my CCNA Voice.  I have access to the study guides and they seem pretty easy.  Just  a though.