Tips on synchronizing a sub-network through a gateway

To synchronize a network through a gateway, router, or firewall the PCs must be able to "see" the IP address of the time server. If there are multiple gateways on the network, the first or "immediate" gateway needs to be programmed into the time server. All gateways, after the immediate one has been programmed, have to be added to the routing tables. To make sure that the PC can see the time server, try pinging the IP address. It will most likely respond to the ping. Pings usually get through even if the tables are not set correctly.

The next thing to try is to make sure Telnet is enabled, at least for a test, in the time server. From the PC, using the command prompt, try to Telnet to the time server using the command: Telnet (IP address of time Server). The response from the time server should be the software version and a prompt for the user to hit the enter key to go into the setup mode. If it does not respond to Telnet, Telnet is disabled in the time server or the IP address is not getting through the gateways. Try this command on the PC in the same subnet as the time server and see if it responds. If it does, the issue is with the address getting through the gateway. If a firewall is installed, port 123 has to be open to let NTP/SNTP packets through.

An alternative to synchronizing a sub-network is to implement an Ethernet time server, such as the model 9188, to uses time from a master GPS time server through direct connection, but has its own IP address to distribute the time behind the firewall.

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Ping test