tunnel interfaces

Unanswered Question
Dec 18th, 2008

How many virtual interfaces can you have on one physical interface?

I have this problem too.
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Richard Burts Thu, 12/18/2008 - 12:14


As a general question I believe that there is not a limit on the number of virtual interfaces on one physical interface, other than the limit on the number of virtual interfaces, which is a function of the number of IDBs and that varies from platform to platform (and sometimes varies by version of IOS). Note that for certain media there may be some limits on the number of virtual interfaces. For example if the physical interface is a serial interface with Frame Relay encapsulation there is a limit on the number of PVCs which would establish a limit on the number of subinterfaces. Or if the interface were a FastEthernet connected to a switch and doing trunking there might be a limit on the number of VLANs supported on that particular switch which would establish a limit on the number of subinterfaces.



Harold Ritter Thu, 12/18/2008 - 12:28


Just to supplement your comment on the number of IDB supported on a given platform (and IOS SW release), you can use the "show idb" command to see that limit.

r1#show idb

Maximum number of Software IDBs 1024. In use 10.


Active 6 7

Inactive 3 3

Total IDBs 9 10

Size each (bytes) 4328 1376

Total bytes 38952 13760

Type SIdx Idx St,O,Sh Interface Name (subblocks)


H 1 1 U,I,R Ethernet0/0 (HW SB CDP(6), MAC ADDR(2), Ether(1))

H 2 2 A,I,R Ethernet1/0 (HW SB CDP(6), MAC ADDR(2), Ether(1))

H 3 3 A,I,R Serial2/0 (HW SB CDP(6), Frame relay(5), Serial(3))

H 4 4 A,I,R Serial3/0 (HW SB CDP(6), Serial(3))

H 5 8 U,D,R Auto-Template1 (HW TUN_TEMPLATE(4))

H 6 7 U,R,R Loopback0

S 1 2 U Ethernet0/0 (SW CDP(3), IPv6(10001), LLC2(1))

S 2 3 U Ethernet1/0 (SW CDP(3), IPv6(10001), LLC2(1))

S 3 4 U Serial2/0 (RSVP(5), SW FR SUB(2), LLC2(1))

S 4 10 D Serial2/0.1 (RSVP(5), Tagswitch(4), SW CDP(3), LLC2(1), SW FR SUB(2))

S 5 5 U Serial3/0 (SW CDP(3), LLC2(1))

S 6 9 U Auto-Template1 (LLC2(1))

S 7 8 U Loopback0 (LLC2(1))

Key: SIdx=Sort Index, Idx=hw_if_index or if_number

St=Current State, O=Old State, Sh=Shadow State

A=Admindown, D=Down, G=Going Down, I=Init

R=Reset, T=Testing, U=Up, X=Deleted




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