CISCO switch - finding DHCP settings for VLANs

[Koldov]

Hopefully a quick question with an easy answer...

 

TL;DR - How do I find if a VLAN is set to use DHCP

 

We run an old network of CISCO switches but I don't have a lot to do with them as they were set up managed before I started and now the support contract has been downgraded to 'break/fix' only and no support on the config side of things.

 

It was setup so that the switches provide the DHCP function, but I have noticed that on a particular VLAN that no I.P.s are given out from DHCP but everything works if I set a static I.P. (other VLANs give out DHCP addresses OK).

 

The main core switch room has the following and I guess was pretty standard for the time (11+ years ago):

 

5508 WLC

 

3750 Master - this has server, printer, admin desktop + access VLAN - TRUNK connections

3750 Member - this has WAP network connections

 

2960 - this has curriculum PC connections (classrooms)

2960 - this has curriculum PC connections (ICT suiite)

 

We have other 2960 switches in other parts of the building which have fibre runs back to the core.

 

Did a little research and then I used PUTTY to TELNET into the 3750 (would this be the correct switch?) and used the commands:

 

show ip dhcp binding

 

show ip dhcp server statistics

 

show ip dhcp pool

 

On the last command I got the error:

3750#show ip dhcp pool

^

% Invalid input detected at '^' marker.

 

I am thinking I might have to specify a 'pool' name, but I don't know what they are (unless they are the VLAN names?). I got as far as finding out this might mean DHCP isn't configured (but I think it must be) so now I'm stuck as the other commands all returned statistics...

 

What I'd like is to get the following info from the switch:

 

1. What VLANs are configured (something like VLAN 10, VLAN 20, VLAN 30)

2. For each VLAN what is the range/scope/pool of DHCP I.P. (VLAN 10 = 192.168.0.1 - 192.168.0.128, VLAN 20 = 192.168.0.129 - 192.168.0.253)

3. Is DHCP configured on each VLAN or not (VLAN 10 DHCP = YES, VLAN 80 DHCP = NO)

4. Also I believe the first 10 I.P.s in each VLAN are reserved for static assignment (out of the range/scope of DHCP pool) so some way to verify that would be good.

[speakercon]

Try 'show running-config' on the 3750. This will show you the full config of the switch including the configured vlans and if they have IP helper address'.

 

I would assume (but not a 100% given) the dhcp will be done on your domain controller so maybe have a look on there what/how the scopes are setup.

Edited February 7, 2023 by speakercon

[Koldov]

Well, that was a lot of effort scrolling and doing copy/paste (which PUTTY didn't seem to like, also I forgot right click was paste like in PS not 'open a sub menu' luckily I wasn't doing any configuration)...

 

But I now have a spreadsheet with all the relevant info...

 

Thanks!

 

EDIT: DHCP is on the core switch, not the DC, don't know why... I guess they thought it was a good idea at the time (not had any major problems though, just a pain when you need to manage - which is rare to be honest).

Edited February 7, 2023 by Koldov