IP and DHCP addressing

Hi
A question on setting IP addresses for modems, routers and switches. I have a 3com modem which has the default 192.168.1.1, sub net mask at 255.255.255.0 and the dhcp range as 192.168.1.2 to 192.168.1.254. The cisco router is on default 192.168.0.1, subnet to 255.255.255.0 and dhcp range 192.168.0.100 to 192.168.0.150.
I am now attaching a switch switch which is also a default IP address of 192.168.1.1 and so I can't get into its control screen to change the settings as the 3com panel comes up at that address. I obviously need to change the IP address of the 3Com but I'm not sure what numbers I can use and whether I would also need to change the sub net mask and the dhcp range - my first attempt led me to having to reset the 3com back to factory after locking myself out so appreciate any help with this and / or a good reference to how addressing works on a home style LAN.
Thanks

If te switch is a Cisco it should have a serial connection which will give access to the management side. If not, then just connect the PC to the switch with nothing else connected and you should be able to log in.

Also, if both have DHCP ranges then you will have two DHCP servers running. You need to turn one of them OFF

The switch is Zyxel and has no serial port, only ethernet so I need to change the 3COM address, just not sure which IP address to use, ie can I use 192.168.2.1 ? Take the point with the two DHCP servers, when I switched off the 3COM modem dhcp was when I got locked out despite having the cisco router DHCP enabled. Thanks

In reply to a post by geoexplore:

The switch is Zyxel and has no serial port, only ethernet so I need to change the 3COM address, just not sure which IP address to use, ie can I use 192.168.2.1 ? Take the point with the two DHCP servers, when I switched off the 3COM modem dhcp was when I got locked out despite having the cisco router DHCP enabled. Thanks

Hi, first disconnect 3Com router from your computer Ethernet port and connect the Cisco switch to your computer Ethernet port, then change the switch IP Address to 192.168.1.2
when configuring the switch make the IP Address Static and outside the DHCP server range, example below�

Configure manually
3Com Router IP Address: 192.168.1.1

Subnet Mask: 255.255.255.0

Enable DHCP
First DHCP Address: 192.168.1.21

Last DHCP Address: 192.168.1.250


Cisco switch IP Address: 192.168.1.2

All must have the same Sub Net Mask 255.255.255.0

Edited by deleted (Tue 16-Aug-11 13:42:55)

Hi, I have tried this - I have the 3Com modem set with an IP 192.168.1.3 which connects to the Cisco router now set to 192.168.1.1 with the DHCP set as suggested and the ZyXEL switch set at 192.168.1.2 , when the router is changed from 192.168.0.1 I lose the wireless internet connection as well which works fine with the router on 0.1, however the direct ethernet connection via the router has never managed to connect to the internet so something is not making it through the router with either the default ot new IP address, any ideas?
Cheers

OK, works now, I had forgotton to switch the static IP address for accessing the switch on the LAN back to automatically assigned. Thanks