[c-nsp] STP and PVST..

Tom Hill tom at ninjabadger.net
Mon May 1 10:17:45 EDT 2017

On 19/04/17 12:20, Catalin Dominte wrote:
> Yes, until you realise that Cisco MSTP does not talk to Juniper MSTP for
> some odd reason! :)

MSTP is quite problematic between vendors, and most of the time the
reason is that certain operating systems - usually Cisco - have certain
VLANs configured by default, e.g. the FDDI VLANs, VLAN 1, etc.

Because these are hard-configured, and can't be removed, to have the
MSTP domain configuration hash properly and match between switches of
different vendors, you often have to create the missing VLANS on other
switches. Even if you don't/can't use them.

I spent a long time getting Cisco 3650s, Brocade CES, and Dell
PowerConnects (5400 and 6200, which are both different) converging with
MSTP, with all root bridges in the right place for each domain. Due to
the wonderful way in which Extreme XOS works, you simply cannot make it

I learnt that RSTP is fine, and you should just use it if you can. If
you can't choose RSTP, turn MSTP on and *don't* configure any domain
name/VLAN-to-instances. The CIST that it creates will interop just fine
with RSTP devices, and most of your interop headaches will disappear.

If you ever get as far as thinking "Man, I wish I could just..." when
configuring STP, please stop. Find a solution that doesn't involve STP,
PVST, or otherwise relies upon a overburdened sprawl of layer-2.

(Mini rant, I might have had it before, possibly. Sorry.)


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