VLSM on a switch

[toeknee2120]

I have searched all over the Internet and can't seem to find the answer to this question.  Everything I've read talks about VLSM but never says specifically if it can be done on just a switch.  All examples have at least 3 routers in them.

Is it possible to configure VLSM on a switch?  I tried doing it at work to optimize our address space on a Cisco 3750G-48 and kept getting "Bad mask..." error.

So...is it even possible?

Thanks in advance for any help you can provide.

[ajay chauhan]

Can you please post what you are trying to do and what you are configuring ?

[cadet alain]

Hi,

of course you can.

Regards.

Alain

[toeknee2120]

Thanks, Alain, for giving me a definite answer.  At least now I know it CAN be done and I can troubleshoot from there.  I'll post the details for everyone else to see in a few minutes.

[ranraju]

Hello Tony,

Yes, as Cadet said, you can have VLSM on 3750 switch.

Can paste the output for what you were trying with the error that you see.

Regards,

ranraju

[toeknee2120]

Thanks, Alain, for giving me a definite answer.  At least now I know it CAN be done and I can troubleshoot from there.  I've never used VLSM, so please correct if I am wrong anywhere.

I was given the subnet 125.12.208.0/20 to use, which should give me 125.12.208.0-125.12.223.255. What I want is the Management VLAN to have at least 30 usable addresses in it and each user VLAN to have 6 usable addresses.

So, am I able to use:

Option1:

125.12.208.0/27

125.12.208.32/29

125.12.208.40/29

125.12.208.48/29 . . .and just keep going up by 8

Or, do I have to use:

Option 2:

125.12.208.0/20

125.12.216.0/29

125.12.216.8/29 . . .and just keep going up by 8

Option 1 is what I was trying to use.  I configured the VLAN 1 with 125.12.208.1/27 and tried to configure the next VLAN with 125.12.208.33/29. If there is no router, would be the default gateway for each VLAN be the network address?

ip routing is on as well as ip classless

[cadet alain]

Hi,

option 1 is ok and each VLAN default-gateway should be the IP address of corresponding SVI.

What is the message you get when configuring this on the switch ?

Regards.

Alain