DNS Issue - Getting Different IPs Assigned

[dajonx]

Hi,

We currently have four Domain Controllers and some have different forwarders. Do you know if this is an issue?

Also, we're getting different IPs assigned on our workstations and are not sure what's causing this. Do you have any idea what's going on?

Any help is GREATLY appreciated.

Thanks!

 

[ShackDaddy]

It's not a problem for them to have different forwarders.

When you say "different IPs" what do you mean? Sometimes that's normal when you are using DHCP and have a short lease time. But they are all IPs in the same subnet, right?

When you do an "IPCONFIG /ALL" from the command-line of a Windows system, you should see a bunch of information including the IP address of your DHCP server. Run that command on several workstations and see if the DHCP server IP is the same on all of them. If any of them have a different address from the others, you may have a problem with a rogue DHCP server on your network.

Dave Shackelford
ThirdTier.net
TrainSignal.com

 

[VinceWhirlwind]

Also, go onto your DHCP service, go to the scope, and check it isn't 100% assigned - if the scope's full, the client will self-assign a default IP address.

If you have a rogue DHCP service on your network (usually a stand-alone wireless router somebody has plugged into the network) you should configure DHCP-snooping on all your switches:
- trust your DHCP server
- trust your uplinks
- configure option 82
- untrust all other switchports

 

[VinceWhirlwind]

To find the rogue DHCP server, check the "ipconfig" off a victim workstation and see what the assigned gateway/router address is.
go to your core switch and ping that IP address on the VLAN the victim workstation is on.
Check your ARP table to get the MAC address that responds to that IP address.
Check the MAC-address-table to see which switchport that MAC address has been seen from.
Go to the switch that is connected to that port and check its MAC-address-table to see where the MAC address is from there.
etc...

 

[dajonx]

Thank you for all of the help!

I found out that it's a certificate issue on a website on IE8 (for some reason, it's not asking for the certificate (ie, it doesn't think that workstation has the certificate installed)). So it's not a DHCP/DNS issue.. Looks like I have to research IE and certificates.

Thanks again!