[c-nsp] spantree pvst and mst

[Asbjorn Hojmark - Lists]

>> See http://tinyurl.com/9rhf7

> Maybe my understanding of VTP pruning was wrong.  I know VTP 
> pruning did what was said in that url above but i also though
> it kept the client switches from seeing vlans that where not
> assigned to ports on that switch. 

Well, not so. They will be sent to the switch, which will then
have to run STP for them. Only then will the switch tell its
uplink which VLANs can be pruned back.

> the 3750's i think support 4000 somthing vlans and the 2950's 
> only support 1024 if i remember correctly.

The 3750 supports 1005 VLANs, but only 128 STP instances.

The 2950 SI supports 64 VLANs, and the 2950 EI supports 250
VLANs, but both support only 64 STP instances.

You're probably thinking of VLAN *numbers* (i.e. 1-1005 or 1-
4096), not the number of concurrent VLANs.

> Shoudnt both sides report the same vlans?

Note that it's saying 'stp forwarding and not pruned'. The will
rarely be the same between a distribution switch and an access
switch.

> VTP makes it easy seeing how i dont have to create/remove 
> vlans on the 2950's also but i guess when that time comes if
> thats my only option i guess i'll have to go that route.

Well, you can also run MSTP.

>> If you want to change from pVST+ to MSTP, you'd better do it
>> in the whole L2 domain. It is possible to mix the two, but it
>> can get kind of tricky. If you do, keep the root inside the
>> MSTP region, not outside it.

> the 3750 is doing routing so i assume your not saying i should
> change my 3750 to MSTP?

Yes, if it's participating the STP, it should preferably be
running the same STP protocol.

> I also dont understand what you mean by keep the root inside
> MSTP region.

There's a fine paper on MSTP on Cisco.com. Just search for
'understanding 802.1s'.

-A