[c-nsp] Number of Switches in MST+

[Dale W. Carder]

I believe that I could characterize my experiences with a large[*] L2 
switched infrastructure as "ugly", specifically with the 3550, and it 
should be avoided if possible.  Cisco touts the model of access, 
distribution, core for a reason and scales and builds their products 
accordingly.  Do it.

About lots of vlans on the 3550, read your release notes for the 
maximum number of "logical interfaces" supported.  This is not SVI's, 
this is the maximum number of spanning tree instances in total that the 
box can handle.  IIRC, this number is 128 for the 3550 and 3750.  Stay 
far, far below this number.

As for code stability on the 3550, IOS is nowhere near fully baked for 
that platform.  Take a look at CSCed65818 (fixed), CSCdx20106 (not 
fixed), CSCdx20106 (not fixed), CSCdx45558 (not fixed).  In summary, I 
would stay well away of any network design that puts a 3550 in a 
situation to have to mitigate spanning tree loops (for redundant links 
in particular) or make any important spanning tree forwarding decisions 
period.  I can't even take credit for that advice, as it was a 
recommendation of Cisco after our last outage caused by 3550's.

The latest version of IOS for the 3550 is better in most regards, or at 
least the 3550 no longer causes network loops and thus broadcast storms 
as easily when the CPU is tasked, and you don't have to send your field 
techs around town to reboot them when the hang as often anymore.

Also, beware of scaling VTP (v2, at least) that large.  Although YMMV, 
I believe that huge VTP domains are generally not recommended.

However, I am a fan of CatOS on 4x00 and 6x00 series switches.

Dale
Network Guy
University of Wisconsin at Madison

[*] A city-wide network, a few thousand switches, a few hundred vlans, 
lots of backhauling/trunking to tens of routers


On Aug 6, 2004, at 12:40 PM, Nicolaj Ottsen wrote:

> Hi,
>
> We are about to expand our MAN, and would like design inputs and 
> generel
> comments.
>
> Today we are running a L2 ring (SpanningTree MST+) build by 7 
> 3550-12Gs,
> all L3 is vlan'nd to 2 6500. We are expanding our ring with 7 new 
> sites.
>
> Does anyone have expirence with running MST+ and vtp with 14 ring
> connected switches, and about 40 switches in total (Good/bad/ugly) ?
>
> I have heard some rumors concerning support for more than 1000 Vlans on
> the 3550 series, and support for upto 16000 vlans on the 6500. Can
> anyone confirm this rumor ? Even better supply us with at release date
> :)
>
> Best regards
> Nicolaj
>
>
>
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