[c-nsp] Maximum spannig tree instances

[Geoffrey Pendery]

Like Gert, I much prefer to have the system running "un-needed"
instances as the tradeoff for not having to design and manage instance
topology, and couple VLANs together, causing TCNs/blocking on VLANs
which haven't experienced any disruption.

"I've wondered about that...if we were to move to MST, we're going to
have to assign every VLAN to an MST instance, which could get messy."

That's exactly why I was warning about the 16/64 instance limit.  This
was my mindset when moving from PVST to MST, and I suspect there are
many others out there thinking this way.  But if you have more than 64
VLANs, you can't do that.  You'll have to look at their topology and
try to map them into a limited number of instances.  Most of the IOS
docs I've found say 16, not 64, but I have yet to test that out in the
lab.

Gert,

I think we mostly agree, and my sarcasm about the "scary proprietary"
bit didn't come across.
It's our management/architects here who are vehemently against the
Cisco Proprietary stuff; I just live with their edicts.
But then again, your statement that RPVST isn't proprietary is wrong,
and the statement that it's not scary tells me you've never tried to
plug it into an Enterasys core...
; )



-Geoff



On Tue, Jul 14, 2009 at 10:16 AM, Jon Lewis<jlewis at lewis.org> wrote:
> On Tue, 14 Jul 2009, Gert Doering wrote:
>
>> On Tue, Jul 14, 2009 at 09:26:13AM -0400, Jon Lewis wrote:
>>>
>>> But isn't that the whole point of MST?
>>
>> We have found MST to be mostly pointless...
>>
>> "Too much hassle, too little gain"
>
> So do you just do rapid-pvst and limit which VLANs are allowed on all trunk
> ports?  I know you're not a fan of VTP, and I suppose this may be another
> reason.  Even with the trunks limiting which VLANs get through, VTP still
> creates all the vlans on all the switches, and in a PVST setup, they run a
> spanning tree instance for each VLAN, even if they aren't really
> participating in the VLAN.
>
>> two VLANs that share the same topology - which maps very poorly to MST
>> instances.  At the same time, there is a fairly high dynamic in adding
>> and removing VLANs, which is *quite* painful with MST instance
>> mappings...
>
> I've wondered about that...if we were to move to MST, we're going to have to
> assign every VLAN to an MST instance, which could get messy.
>
> Maybe it is time to just turn off VTP and manually create VLANs only where
> they're needed, in which case we'll only have to worry about the number of
> PVST instances on the central 6509s, as there's no way we'd run up to 128
> VLANs on a 3550.  We've actually never done VTP on the 6500s...only on the
> 3550s.  I figured if VTP ever did blow up, I didn't want it blowing on the
> central switches...just the edges.
>
>
> ----------------------------------------------------------------------
>  Jon Lewis                   |  I route
>  Senior Network Engineer     |  therefore you are
>  Atlantic Net                |
> _________ http://www.lewis.org/~jlewis/pgp for PGP public key_________
>