Subinterface limitation in a Switch

[vivek_mohta]

We have a 4908G Switch and have configured multiple subinterfaces in the Switch. We are now unable to add any further subinterface in the Switch and are getting the following error :-

INTERFACE_API-1-NOMORESWIDB: No more SWIDB can be allocated, maximum allowed 300

-Traceback= 600737BC 6008F3A8 60098D6C 60090348 6004B18C 6004BB6C 600571C4 60099044 60099030

46w3d: %PARSER-3-CREATEINT: Can't create any more subinterfaces

We then tried to remove some of the subinterfaces associated BVI/bridge group from the configuration and we got the following error :-

4908G-IT_MSR(config)#no interface gigabitEthernet 7.72

% Not all config may be removed and may reappear after reactivating the sub-interface

Now the subinterface doesnt show in the running configuration but when i type the command

# show ip interface brief

GigabitEthernet7.72 unassigned YES unset deleted down

Now that I need to create more subinterfaces which should I do ?

[Bobby Thekkekandam]

Hi Vivek,

The error you're getting "No more SWIDB can be allocated" is a result of you running out of "software Interface Descriptor Block (IDB)" SWIDB. Here's some information on IDB:

http://www.cisco.com/warp/public/63/idb_limit.html

When you delete an subinteferface, the SW IDB remains in the memory. Her's an example of what happens when you delete a subinteface:

*************************

-11-5-7206-115#sh idb

Maximum number of Software IDBs 20050. In use 28.

HWIDBs SWIDBs

Active 14 20

Inactive 8 8

Total IDBs 22 28

Size each (bytes) 4656 1392

Total bytes 102432 38976

9-11-5-7206-115#conf t

Enter configuration commands, one per line. End with CNTL/Z.

9-11-5-7206-115(config)#no int atm3/0.1

Not all config may be removed and may reappear after reactivating the sub-interface

9-11-5-7206-115(config)#end

9-11-5-7206-115#sh idb

Maximum number of Software IDBs 20050. In use 28.

HWIDBs SWIDBs

Active 14 19

Inactive 8 9

Total IDBs 22 28

Size each (bytes) 4656 1392

Total bytes 102432 38976

*************************

As you can see the "Total IDBs" under "SWIDBs" remain. The only thing that's changed is the number

of "Active" and "Inactive" after I deleted the interface.

SW IDB is created in memory. The only way to clear the IDB is by reloading the router after deleting a subinterface. Once you reload it, you can create different subinterfaces.

HTH,

Bobby

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[vivek_mohta]

Thanks ,

The problem got resolved by rebooting the switch

[Richard Burts]

Even when you do no interface gigabitEthernet 7.72 some elements of the interface remain, as you have found out. The reasons have to do with how the running conf works - it is not a text file as we tend to see it but is a binary data structure. When you remove the subinterface (with the no interface command) some elements of the binary data structure were initialized and remain. The way to really get rid of them is to remove them (with the no interface command), save the config, and reload the switch. Then they will really be gone and you should be able to create new subintefaces.

HTH

Rick