[e-nsp] vlan trunk between summit 400 and cisco 3750

[Mikael Abrahamsson]

On Sat, 26 Aug 2006, Yu-lin CHANG (seawind) wrote:

> I don't know why S400 sends tunking information to those
> "untagged" ports.

It doesn't. It just forwards the spanning tree packets without doing 
anything about them. Most likely it's the 3750 that runs PVST or some 
other STP on the vlans you're trunking to/from it and this gets forwarded 
by the S400 as any other packet, and then the 2900 has some default 
protection turned on against this case and complains.

I usually say that Cisco switches are the Macintoshes of the switch world. 
They have a lot of things turned on that "just works" in a pure Cisco 
environment, but as soon as you start to interconnect them with other 
brands, you really have to know everything they do and don't and handle it 
by turning off things or changing the defaults.

"no spanning tree vlan 100" and 200 on the 3750 might solve this problem, 
or turning off bpdu-guard on the 2900.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se