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Maximum number of SVI\VLAN interfaces in the switch

Hi guys,

 

I can't find any clear information about supported or recommended number of maximum VLAN interfaces in any switch.

I've found this document - http://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-122-mainline/15096-idb-limit.html#idb_limits but it describes routers.

 

I will be appreciate if any information.

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Hall of Fame Cisco Employee

Hello Ruslan,

Hello Ruslan,

One of limitations is given by the maximum count of so-called Interface Descriptor Blocks (IDBs). These IDBs are software data structures that describe the properties of individual interfaces, either physical or virtual, of a router or a switch. There is one IDB allocated for each interface. The maximum counts of IDBs that can be created is strongly dependent on the device platform and IOS version. A device can never have more interfaces than the maximum allocatable number of IDBs. To find out the current number of allocated IDBs and maximum count of IDBs, you can use the show idb command:

Switch# show idb

Maximum number of Software IDBs 5474.  In use 86.

                       HWIDBs     SWIDBs
Active                     82         82
Inactive                    4          4
Total IDBs                 86         86
Size each (bytes)        3392       1528
Total bytes            291712     131408
[ ... output omitted ... ]

This particular Catalyst 3560 tells me that the maximum number of IDBs is 5474, and we're already using 86, so there's a plenty of further space.

This is not the only limit, however. Usually, lower-end Catalysts do not support more than 255 or 1005 simultaneously existing VLANs, and without a VLAN, the corresponding interface Vlan will not be usable. So the maximum number of supported VLANs also influences how many Vlan interfaces you can use. You can check this maximum number of supported VLANs in the show vtp output:

Switch# show vtp status
[ ... cut ... ]
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 38
VTP Operating Mode              : Server
[ ... cut ... ]

It should also be noted that each routed port on a multilayer switch (i.e. a no switchport port) consumes one specific VLAN just for itself (these are so-called internal usage VLANs), so using routed ports instead of Vlan interfaces does not result in any conservation of resources.

There also may be another indirect limits imposed, such as maximum supported number of simultaneously running STP instances (usually, only up to 128 STP instances are supported so either you need to use less than 128 VLANs, or use MSTP to decouple spanning-tree instances from VLANs) or others, but these are the ones I am acutely aware of.

The maximum number of IDBs and VLANs is platform and IOS specific, so it is generally difficult to produce a universally applicable table summing these numbers.

Perhaps this helps somewhat.

Best regards,
Peter

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Peter, thanks for your quick

Peter, thanks for your quick and comprehensive answer.

as I understand there are no documentation/guides for such things like limit of VLAN interfaces and I'd like to know these numbers before I buy particular switch model:).

also could you tell me exact model of your switch and version of IOS?


is there anyone who may know about such numbers in other switch models?

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