2960 showing multiple SVI's as up

Unanswered Question
Oct 17th, 2007

I was just asked to look at a config and was amazed to see that 2 SVI's shows up in a layer 2 switch. Is it a bug?

Switch#sh ip int brief

Interface IP-Address OK? Method Status Protocol

Vlan1 unassigned YES NVRAM up up

Vlan6 172.20.103.2 YES NVRAM up up

Vlan10 172.20.104.2 YES NVRAM up up

FastEthernet0/1 unassigned YES unset up up

Switch#sh ver

Cisco IOS Software, C2960 Software (C2960-LANBASE-M), Version 12.2(25)SEE2, RELE

ASE SOFTWARE (fc1)

Copyright (c) 1986-2006 by Cisco Systems, Inc.

Compiled Fri 28-Jul-06 04:33 by yenanh

Image text-base: 0x00003000, data-base: 0x00AA2F34

ROM: Bootstrap program is C2960 boot loader

BOOTLDR: C2960 Boot Loader (C2960-HBOOT-M) Version 12.2(25r)SEE1, RELEASE SOFTWA

RE (fc1)

Switch uptime is 2 days, 1 hour, 4 minutes

System returned to ROM by power-on

System image file is "flash:c2960-lanbase-mz.122-25.SEE2/c2960-lanbase-mz.122-25

.SEE2.bin"

cisco WS-C2960-48TT-L (PowerPC405) processor (revision B0) with 61440K/4088K byt

es of memory.

Processor board ID FOC1042ZCDE

Last reset from power-on

3 Virtual Ethernet interfaces

48 FastEthernet interfaces

2 Gigabit Ethernet interfaces

The password-recovery mechanism is enabled.

interface Vlan6

ip address 172.20.103.2 255.255.255.0

no ip route-cache

!

interface Vlan10

ip address 172.20.104.2 255.255.255.0

ip helper-address 172.16.42.27

no ip route-cache

!

Narayan

I have this problem too.
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glen.grant Wed, 10/17/2007 - 06:12

doesn't seem right , also like the helper address on the one SVI . Someone who did this thinks this box will route apparently , don't know why both SVI's are up though .

Kevin Dorrell Wed, 10/17/2007 - 06:37

Although this is a layer-2 switch, they have finally allowed it to have a presence in more than one VLAN at a time. That doesn't mean it can route. It just means that you have more than one way of getting at the box if one of your VLANs is down.

Kevin Dorrell

Luxembourg

royalblues Wed, 10/17/2007 - 07:10

Kevin,

even i thought the same but how will you define the gateway of the switch in that case.

Say for example if i have following configuration

int vlan 6

ip address 172.20.103.10 255.255.

ip defaul-gateway 172.20.103.1

Now if this vlan is down, i cannot logon to this switch remotely but need to log on to the upstream switch and telnet again.

Anyway before i could not do any R&D on this, the engineers changed the config. I will try to simulate the same with one of my 2960's

Narayan

Kevin Dorrell Wed, 10/17/2007 - 07:18

You will not be able to get to it from VLAN 6 any more, sure. Even if you go through a router. But you should be able to get to one of its other IP addresses from something on the same VLAN as that address. I agree though that if it doesn't have a viable default-gateway then it will not be able to talk to any subnet where it does not have a presence.

Kevin Dorrell

Luxembourg

royalblues Wed, 10/17/2007 - 08:45

Well let me figure out whether it is really a new feature that cisco has introduced or is just another cosmetic bug :-)

Narayan

ankbhasi Wed, 10/17/2007 - 11:14

Hi Narayan,

It is not a bug actually. Multiple SVI support feature was introduced in 12.2 train and because 2960 switch supports 12.2 train this feature is available on this switch but as you already know it cannot route beteen vlans and only one default gateway is possible there is no much use of this feature on this hardware platform.

HTH

Ankur

*Pls rate all helpfull post

Alexander Demin Fri, 12/24/2010 - 01:35

Sorry, I have to update such an old topic ;-)

Unfortunately, I did't find such a feature (multiple SVI support) in Cisco Feature Navigator, nor I found any info about such support in 2960 datasheets.

Could anyone point me to the way I can definetly say abt. this or that switch that it has support for multi SVI ?

wbr, Alex.

ankbhasi wrote:

Hi Narayan,

It is not a bug actually. Multiple SVI support feature was introduced in 12.2 train and because 2960 switch supports 12.2 train this feature is available on this switch but as you already know it cannot route beteen vlans and only one default gateway is possible there is no much use of this feature on this hardware platform.

HTH

Ankur

*Pls rate all helpfull post

Peter Paluch Fri, 12/24/2010 - 01:55

Hi Alex,

When 2960 Catalyst switches were rolled out, I have been also surprised to learn that there can be multiple SVIs activated. That was a strong departure from the style of configuration I've been used to seeing on 2900XL and 2950 Catalysts.

The fact is that I do not know if this "feature" is actually something that has a special name and that may or may not be present. Using the Feature Navigator for this probably won't be useful. The documentation is also not very explicit about this. I am afraid that finding out whether this or that switch supports multiple active SVIs is a detective work for now.

Then again, for a pure Layer2 switch, it does not make much sense to support multiple active SVIs. Or does it?

Best regards,

Peter

Alexander Demin Sat, 12/25/2010 - 13:00

Hello, Peter!

It does makes sense even for pure L2

Just an example:I deploy a layer 2 channel for a client in my switching cloud from one edge to another. This channel is actually a VLAN.

A good diagnostic procedure for me to test the consistency of the channel from edge-to-edge is to push up two SVI's with IP addressing (one on each edge switch) and use ping. Of course, there is layer 2 traceroute (traceroute mac), but if CDP does not present everywere on the net - it doesn't work.

wbr, Alex.

Peter Paluch Sat, 12/25/2010 - 13:39

Hi Alex,

Well, yes, that is an example of a nice use of multiple SVIs even on a L2 switch But originally, the only active SVI as seen on 2900XL/2950 switches was used to provide a connection of the switch CPU into a single management VLAN for management and control purposes. Using a switch as a test target is... well, beyond its scope

But sure - invention has no limits.

Best regards,

Peter

glen.grant Sun, 12/26/2010 - 11:22

    With the latest release of code for the 2960 it is no longer just a L2 switch and

is now a limited function layer 3  switch also  , no dydnamic routing but static routing

off the switch is possible.   It will intervlan route on the switch itself.

Peter Paluch Sun, 12/26/2010 - 12:36

Hi Glen,

Sure, I know about that (and I silently expected someone to point that out ). The question is: was that the original intent since the first time the 2960 were introduced? I guess this can be answered only by a product manager. In any case, if that indeed was the intent then the multiple SVIs are logically supported since the first IOS version.

Best regards,

Peter

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