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New Member

Maximum Vlan support on 2940 series switch


I am using WS-C2940-8TF-S switches and i need to cofigure around 25 Vlans but i am not able to cofigure it. Below is the VTP STATUS output.

The maximum no of VLAN is now only 8, but current requirement is to support more than 25 VLANS each of the Switchs. If IOS is require to resolve the problem.

Please provide the solution at earliest.

Edge_M&M_2940#sh vtp sta

VTP Version : 2

Configuration Revision : 0

Maximum VLANs supported locally : 8

Number of existing VLANs : 7

VTP Operating Mode : Transparent

VTP Domain Name : ABCD

VTP Pruning Mode : Disabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

MD5 digest : 0x70 0xBF 0x4C 0x6B 0x71 0x04 0xE7 0x58

Configuration last modified by at 3-1-93 00:32:53

sh ver

Cisco Internetwork Operating System Software

IOS (tm) C2940 Software (C2940-I6Q4L2-M), Version 12.1(19)EA1c, RELEASE SOFTWARE (fc2)

Copyright (c) 1986-2004 by cisco Systems, Inc.

Compiled Mon 02-Feb-04 22:53 by yenanh

Image text-base: 0x80010000, data-base: 0x80594000

ROM: Bootstrap program is C2950 boot loader

Edge_E&T_2940 uptime is 18 minutes

System returned to ROM by power-on

System image file is "flash:/c2940-i6q4l2-mz.121-19.EA1c/c2940-i6q4l2-mz.121-19.EA1c.bin"

cisco WS-C2940-8TF-S (RC32300) processor (revision C0) with 20776K bytes of memory.

Processor board ID FHK0817Y0J9

Last reset from system-reset

Running Standard Image

9 FastEthernet/IEEE 802.3 interface(s)

1 Gigabit Ethernet/IEEE 802.3 interface(s)

The password-recovery mechanism is enabled.

--More-- 32K bytes of flash-simulated non-volatile configuration memory.

Base ethernet MAC Address: 00:0F:90:28:A1:80

Motherboard assembly number: 73-8783-05

Power supply part number: 341-0085-01

Motherboard serial number: FOC08151XX6

Power supply serial number: HIC080600PF

Model revision number: C0

Motherboard revision number: A0

Model number: WS-C2940-8TF-S

System serial number: FHK0817Y0J9

Configuration register is 0xF



Re: Maximum Vlan support on 2940 series switch

IOS will not solve your problem . The question becomes how can you need 25 vlans on a 8 port switch ??? These are not made to be aggregation switches , really only for small offices. You have the switch in transparent mode so vtp does not really come into play here.

New Member

Re: Maximum Vlan support on 2940 series switch

Hi Glen…I think I could not explain it properly. Let me explain fist -

I have configured 3750 core switch with more than 25 Vlans under Server Mode and my edge switches (2940 8Port) is configured with client mode edge switches having IOS (c2940-i6q4l2-mz.121-19.EA1c/c2940-i6q4l2-mz.121-19.EA1c.bin) .

The problem which I am facing here is-

1) All 25 Vlans configured on the core switch (3750) are not propagting to edge switch (2940 8Ports)

2) Edge Switch VTP Client mode automatically changes to transparent mode (while i thought transparent mode could not affect the Vlan propgation but still why mode is automatically changing).

While I am putting edge switches into production VTP mode auto changed from Client to transparenet & all Vlan information is not propagated into edge switches.

I would like to know -

How can we verify for a particular switch ( of any series) is supporting how many no . of the Vlans? Is there any a co-relation with IOS or it is hardware specific?

Thanks in Advanced


Hall of Fame Super Silver

Re: Maximum Vlan support on 2940 series switch

Hello Jintedra,

I have seen same kind of problems between C6500 and C2950.

There are two limits that can be different:

maximum number of Vlans that can be accepted in a VTP update

maximum number of STP instances.

In your case as in mine, the access C2940 switches revert to transparent mode to protect themselves from an excessive number of Vlans in the VTP update.

Once they are in VTP transparent mode you need to create the required vlans on each switch manually (you cannot be sure the 8 accepted vlans are good for all switches)

You need also to configure on the core switch each trunk port with a manual list of permitted vlans:

int f0/3


switchport enc isl|dot1q

switchport mode trunk

switchport trunk allowed vlan x,y,z,k

Hope to help


New Member

Re: Maximum Vlan support on 2940 series switch

Hi Giuseppe...Please let me clear few more points as described below -

1) Do I need to add all Vlan on edge switch manually or only isolated Vlan's (as Vlans are propagating dynamically may be in next VTP update revision Vlan sequence will change?).

2) As switch is not capable to cope the excessive vlan. Pushing manual the Vlan on edge switch can work... how? is it due to any IOS flaw or any other concept?

3) Changing mode from client to transparent due to excessive Vlan is a cisco switch behavior or is there any the logic behind it

Jitendra !!!


Re: Maximum Vlan support on 2940 series switch

To get around this problem on the trunk links on both sides restrict the vlans that are allowed across the link "switchport trunk allowed vlan XX" . If you need say 3 vlans on the 2940 only allow those 3 vlans across the links on both sides . The vlan database on the 2940 will still show all 25 vlans if you do a show vlan but the 2940 does not allocate a spanning tree instance for anything that is not allowed on the trunk and that is in where the problem lies. The 2940 probably does not support more 8 spanning tree instances so anything over that it will change it to transparent mode . If you restrict the vlans allowed across the link to less than 8 it should not automatically change to transparent mode . We had the issue with some 2950's where we had like 90 vlans on a 6500 defined and the 2950 only supported like 64 instances , once we manually pruned off the vlans allowed it worked fine. The restriction is a hardware restriction , the 2940 is a very small switch used for small offices and really isn't suited for installations where you are going to need dozens of vlans. What you are seeing is normal switch behavior due to the hardware restrictions on the switch.


Re: Maximum Vlan support on 2940 series switch

A litte more info , earlier versions of code seem to indicate they only support a small number vlans and spanning tree instances .In looking at the latest code information it seems to indicate support for a much larger number vlans and spanning tree instances like 128 so you can either upgrade to the latest code which is like 12.1.22ea11 or you can manually prune off the vlans to less than 8 in your current setup , personally I would do both. Info from 12.1.22ea11 config notes.

Catalyst 2940 switches support 128 VLANs. VLANs are identified with a number from 1 to 4094. VLAN IDs 1002 through 1005 are reserved for Token Ring and FDDI VLANs. VTP only learns normal-range VLANs, with VLAN IDs 1 to 1005; VLAN IDs greater than 1005 are extended-range VLANs and are not stored in the VLAN database. The switch must be in VTP transparent mode when you create VLAN IDs from 1006 to 4094.

The switch supports per-VLAN spanning-tree plus (PVST+) with a maximum of 64 spanning-tree instances. One spanning-tree instance is allowed per VLAN. See the "Normal-Range VLAN Configuration Guidelines" section for more information about the number of spanning-tree instances and the number of VLANs. The switch supports IEEE 802.1Q trunking for sending VLAN traffic over Ethernet ports.

Hall of Fame Super Silver

Re: Maximum Vlan support on 2940 series switch

Hello Jitendra,

Glen has answered very well to your questions

about question 3) the logic is that of protecting from a VTP DB that is too big.

note that VTP updates should be not partial so there are no chances to be able to digest smaller updates in the future so the only possible choice is to become VTP transparent

Hope to help


New Member

Re: Maximum Vlan support on 2940 series switch

Hi Glen/Giuseppe,

Thanks for your valuable responses. please clear my below points a little bit more-

- to execess no. of STP instance it is happening i.e possible only when we use PVST+/MST but When we are using CST (single STP) for all Vlan then will it work?

- existing hardware could not support the requirement & there is no any other other way to get problem resolved except H/W upgarde ?

- Is upgarding the IOS (ver 12.1.22ea11) will solve the problem?

- now here you are saying catalyst 2940 support 128 Vlan it means my existing hardware is capable to cope the requested Vlan (no. 25) just need to upgrade the IOS to Version 12.1.22ea11 ?