Cisco Switch Maximum number of VLAN support

[johnlloyd_13]

hi,

i'm going to standardize the L2 STP in one of our facility.

i tried to search for the maximum number of VLANs supported in a cisco switch but some links/doc are very old and inconsistent.

my question is, what determine the maximum number of VLANs supported in a cisco switch? is it the platform/hardware, VTP version, or STP version (MST, PVST+, etc)?

we got switches using extended VLAN id 1000+ and would like to determine if STP (i got a mix of MST, PVST, RSTP), on the switch will support it. is there a unique/other command to check this aside from the usual 'show span'?

[Giuseppe Larosa]

Hello @johnlloyd_13 ,

in my experience it is platform dependent and there are two different values:

a) max numbers of VLANs in database

b) max number of STP instances ( very important for PVST and Rapid PVST)

The two values can be different in the same platform at least it was in the past.

if a switch receives in VTP a too large database it moves itself to transparent mode and will not have the exceeding VLANs

the STP limit that can be lower for example 64 with limit in vlan database 128 was much more subdole as VLANs were added successufully but no STP instance was running for that VLAN.

The best solution for STP scalability would be moving to MST .

Modern switches limitations for type a) limit are reported in data sheets and are typically 1024 or 4094. The limitations on STP are not so available.

note a limit of 1024 VLANs means 1024 concurrent VLANs taken from the range 1-4094.

with VTPv3 the concept of extended VLANs ends and also VLANs with ID > 1024 can be advertised and propagated.

To be noted VTPv3 can also propagate MST configuration using an additional database and this makes the pair VTPv3 and MST a very good choice as it solves the issue caused by a change in MST that would need to be propagated to all switches in the same region.

Hope to help

Giuseppe

[Joseph W. Doherty]

I believe Giuseppe has hit all the high points, specifically that such limits can vary per platform and such are, often, not well documented.  Also, not 100% positive, but limits might also vary within a switch series, between different models, and, perhaps, even occasionally, with major IOS version changes.  (The latter might be seen between an "early" version of an IOS for the platform and a later version.)

I would also second Giuseppe's recommendation to use MST if you have "lots" of VLANs running PVSTP.  (One thing I've noticed on many Cisco switches, because dedicated hardware handles the normal data plane traffic, their CPUs are often not very powerful, as they seemed to be sized for typical/normal control plane processing.)