Here's our topology:
SBS 2003 DC
Cisco 1841 Router
Linksys SLM224G 24 Port Switch
Domain Controller IP - 192.168.12.2
Cisco 1841 Router
Dell Powerconnect 16 port switch
Domain Controller IP - 192.168.10.2
Office connected to Main Office through Point to Point T1
Server 2003 DC - IP 192.168.11.2
Linksys Rv0041 Router
Dell Powerconnect 16 Port Switch
Office connects to Main Office through Server to Server demand dial vpn
This office also has an outward facing IP that allows me to RDC into the DC
Last night I was attempting to install a new Dell 2748 switch in our main office. I planned to leave it in unmanaged mode. I swapped the linksys switch with the new Dell Switch and I could no longer ping my remote domain controllers from the Main Office. Obviously, I also started getting replication errors in the event log. My VPN connection between the Main Office and Remote2 are still up. And the point to point VPN between Main Office and Remote1 is still up. From the Main Office DC, I can ping clients through the T1, but just not Remote1 DC. I can, however, access network shares from the Remote1 DC. When I ping by servername, remote1DC, it does resolve to the proper IP address.
As a panick move, this morning, I swapped back to the old linksys switch, but that hasn't helped.
Other interesting notes:
From remote1 DC, I can ping Main Office DC and all clients at Main Office
Clients at Remote1 can't ping Remote1 DC, but can ping anything in the main office.
Actually, the only computer that can ping the remote1 dc is remote1 dc itself.
Pinging remote1dc from either the remote1 or main office routers fails also.
As I wrote earlier, I can usually RDC to remote2 DC through an external IP address in cases where site to site connectivity fails (such as this!). However, even this doesn't work.
It's as if the nics on the two remote DCs are now locked.