SubInterface on a router

Question

How many sub interfaces can be created on a cisco router to route between vlans on a connected switch?

Answer 1

Maximum Number of Interfaces

Every interface uses an IDB. Therefore, the IDB limit indicates the maximum number of interfaces a router can handle.

The IDB limit is, therefore, the answer to the common question "How many (sub)interfaces can be configured on this platform?"

Maximum Number of VLANs

Each Virtual LAN (VLAN) requires one IDB. Any Cisco IOS software release can support up to 4096 VLANs (0-4095, where the number range is 1 to 4094 and in which 0, 4095 are reserved), if the platform supports at least 4000 IDBs

There is a limitation of 256 bridge groups in the Cisco IOS software release if you use VLAN bridging.

"Maximum Number of Interfaces and Subinterfaces for Cisco IOS Routers: IDB Limits"

If you are alluding to a router on a stick scenario (?) then it will depend on how many IDBs the platform can handle. A SWIDB represents a logical sub-interface and you can use the IOS command 'show idb' for existing allocations and the memory consumed.

Each interface uses an IDB and the limit therefore indicates the maximum number of interfaces a router can handle.

You need to know how many IDBs your particular platorm can configure (see above). Commonly this can correlate to the max number of vlans configurable because each vlan will require 1 IDB (normally 4094 in cisco IOS).