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Time Syncing Through a Firewall Without NTP?

Posted by Cliff on from the route-around-the-problem dept.

dvdsmith asks: "Say are dealing with a Windows network that for internet access must pass through a firewall that you have no control over. Said firewall apparently blocks the known time protocols (NTP,daytime,etc) and you know from experience that those who control it will not allow any exceptions. If one sets up an internal NTP server (Windows XP or 2000 workstation) for all others to sync from, is there another reliable method for updating time on the server, like pulling from a Java website? See the time.gov website as an example. Any ideas?"

7 of 112 comments (clear)

  1. COOKING WEB SERVICES WITH ELZAR by captnitro · · Score: 5, Funny

    Of course, your most important ingredient is this baby right here: the external web service. You can get it in a can but to really do things right, you gotta strangle yourself a fresh one.

    We're going to sync with our outside web service using a simple SOAP client, written in whatever language you prefer, and setting the time. (Your users will get their time from you via NTP still, of course.) This isn't required, but for that fresh BAM! taste, it's recommended. Mind the delay calculations if you're writing the client side of it yourself, the WWWait will have a little bit more effect here depending on your setup. If you want to make it quick and dirty, there's no reason to go through the SOAP/WSDL hoops, the point is having it on a known port and piggybacking across HTTP's fame and success, and then sleeping with its girlfriend, and stealing her wallet on the way out. BAM!

  2. Here's what I'd do... by Anonymous Coward · · Score: 5, Insightful

    Ask the morons in charge of the firewall to please open the NTP port and take the time to explain why this is important.
    Take it up with management if said morons disagree.

    1. Re:Here's what I'd do... by ColaMan · · Score: 4, Insightful

      Get quotes for your time-sync hardware, and a *formal* quote from IT. (if no formal quote is forthcoming, keep your evidence of attempting to obtain one, and do a best-guess yourself, factoring labour/bandwidth/etc).

      Go up the chain to whoever manages both the IT and your division. Say "We need time sync for such-and-such. It's necessary."

      Give them a breakdown of costs like so:

      $x for GPS stabilised NTP appliance.
      $y for some bonehead in IT to open the port up.

      Make sure you put the expensive one first. If it costs the IT department more to poke a hole in the firewall, well, hell, you'll get a new toy to play with. But most likely management will say (paraphrased) "WTF? Bring me the head of the IT department manager, on a silver platter."

      IT departments are there to provide services for the rest of the company. That's their job. If they're not doing their job, call them on it. They're just a lead weight around the company's neck otherwise.

      --

      You are in a twisty maze of processor lines, all alike.
      There is a lot of hype here.
  3. Tunnel. by SharpFang · · Score: 5, Informative

    Set up a host outside the firewall, and tunnel the NTP data over some "allowed" port, so it gets through. Or set it up as NTP server on non-standard port (80?) outside the firewall.
    If you want precise measurement, this is the way to go. NTP software will correct the latency errors, no matter if you have direct connection or if it goes through tunnels around the globe, so you have precise time. But if you go for methods like reading time from website applet, all the network latency problems get completely neglected and just add up to the error of the internal server. You could just as well sync it to your hand watch instead.

    --
    45 5F E1 04 22 CA 29 C4 93 3F 95 05 2B 79 2A B2
  4. radio by F�an�ro · · Score: 4, Interesting

    you could build a device that gets the time via radio (LINK) or buy one that does this (like a gps receiver?).

    or if any udp port is open in the firewall, set up a ntp server outside that answers on that port

  5. You should use NTP by Anonymous Coward · · Score: 5, Insightful

    Correct subsecond time is important.

    If your boxes are hacked and you go into court and you can't demonstrate that your log timestamps have anything to do with reality, you might not be able to use them as evidence.

    You also would like to be able to accurately judge HTTP cache timeouts and other time-sensitive things.

    You also don't want your time to "step" (jump by more than one second) if you can help it. It screws up sensitive daemons and I've seen more than one box crash and burn and start spawning crap when the clock jumped backwards.

    Have them open up the damn firewall, set up a reliable Unix-based NTP server on the inside that syncs to something outside, and have the workstations sync up with that.

    You CANNOT tunnel NTP over SSH. NTP uses UDP.

    You also don't want to just get the time from some web page and set the clock because your clock may jump, and you don't adjust for latency correctly either (NTP is *complicated* because there are a lot of edge cases and complex concepts here). Also you'd like to be able to select from multiple sources and throw out any outliers, in case one has been hacked.

    If you can't do the sane thing, which is open up the firewall, you can just set up a local Unix NTP server and at least your boxes will all have the same time as that box, even if it's the "wrong" time.

    You can also use GPS or a dialup modem to set the time on your NTP server.

    To recap:

    1) set up a centralized NTP server
    2) sync to that NTP server
    3) if possible, sync that NTP server to another external NTP server, OR a radio or modem signal.

    It ain't rocket science folks.

  6. "Atomic Clock" card by SA+Stevens · · Score: 5, Informative

    You can run a local NTP server, and install an 'Atomic Clock' receiver in it, on a Card. Basically it's a 10 MHz WWV receiver that decodes the time info and reads it into the PC. They've been around a long time.