Cisco router 1941 completely giving wrong IP and DNS address

[prompt2k2]

I have configured the ROuter 1941 successfuly and been in use for about 5 months, and just this morning, I realised some systems are not able to connect to the internet, on investigation I realised they do not have the correct IP and DNS address, they will connect to internet when I manually assign the IP and DNS address, what could be the cause and possible solution, i have checked the config and the DHCP pool and the DNS address configured on the router still remain correct.

Please help.

[mahmoodmkl]

HI

I think someone has introduced a cable modem in u r network,kindly check in to this,

[prompt2k2]

Hi Mahmoodmkl,

what do you mean by a cable modem? please elaborate.

[mahmoodmkl · Accepted solution]

Hi,

It seems somone has enabled DHCP server in ur network which is leasing these IP's.

Thanks

[Oleksandr Nesterov]

Hi Seun

It also can be a small router/wi-fi point etc.

You can check leased addresses via command "sh ip dhcp binding"

Just install wireshark on one of the PC's which gets wron address and renew the address.

If you'll get wrong ip you will see from which address you have received it - this will be rogue dhcp server address. Then just check the mac on the switch to find out the port to which server is connected.

HTH,

Alex

[prompt2k2]

Yea, Thanks,

Once you mentioned that, I realised one of the access point may have been the cause, and it turns out it is.

All I did was to disable the DHCP server on the Access Point.

Everything is fine now.

Thanks