Brocade VDX Switches – line protocol down / ISL DOWN

It would seem that it’s rather difficult (not possible?) to deactivate the ISL exchange between Brocade switches. This normally isn’t a problem unless you really want to segment your Brocade switches by not running ISL trunking between certain ones. As soon as you want to do this you may come across your interface in this state:

line protocol down (ISL DOWN)

Points you in the direction of ISL but when you’ve explicitly disabled fabric ISL for the interface:

no fabric isl
no fabric trunk

You may be left wondering how to disable it. We tried a few things but the Brocade ISL seems to operate at a lower level than the commands presented in NOS. Anyway the eventual solution was simply to change the vcs ID:

vcs vcsid XXX

Where XXX is different to your other switches.

It’s probably the cleaner solution in any case. Had we set things up properly in the lab in the first place then we wouldn’t have encountered this issue at all, but then again we now have the knowledge that NOS is doing things behind the scenes at a lower level than we’ve really got access to (when vcs mode is enabled). I guess it’s always nice to discover this in a lab environment first anyway.

Our first production deployment of Brocade VDX6740 & VDX6710 switches will be occurring later this week in Perth Australia. We’re really enjoying the multi-chassis LACP within a vcs fabric feature (I’m not sure any other switching fabrics support this?). It gives us an opportunity to do some fancy redundancy deployments – at least that’s how it’s working in the lab – watch this space for some real world experience coming up soon!