Server 2003 - unable to establish any network connectivity

An un-official state of emergency was declared when receiving this problem!!

Microsoft Windows Standard server 2003 (presumably also applies to SBS 03)with two network cards was unable to access the internet and the local network even though both cards are showing connected in the Status panel.

After checking all of the IP services and settings were correct, I tried a Network connection repair to get the message "Windows was unable to repair the connection, unable to clear the arpcache" Seeing this error before, I cleared the cache manually in DOS and repaired the RRAS Service...Still no joy.

The actual resolution was in relation to the IPSEC service not starting correctly and upon manual startup you are presented with:

"only one usage of each socket address (protocol/network address/port) is normally permitted."

As you may or may not know if the IPSEC service fails to start, the server will be running in Block mode and it will block all network connectivity to the server.

To fix this you must enter the registry and correct the following:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\

Select ReservedPorts

and make sure the entry reads as follows:

1645-1646 - Used by IAS
1701-1701 - Used by L2TP
1812-1813 - Used by IAS
2883-2883 - Used by AUTD
4500-4500 - Used by IPSEC

Please note a reboot is required once making the change

For further details see this related link.