{"id":482,"date":"2013-08-25T14:21:25","date_gmt":"2013-08-25T12:21:25","guid":{"rendered":"http:\/\/bergs.biz\/blog\/?p=482"},"modified":"2013-08-25T14:21:25","modified_gmt":"2013-08-25T12:21:25","slug":"how-to-roll-your-own-dyndns","status":"publish","type":"post","link":"https:\/\/bergs.biz\/blog\/2013\/08\/25\/how-to-roll-your-own-dyndns\/","title":{"rendered":"How to roll your own DynDNS…"},"content":{"rendered":"

I didn’t want to rely upon services like DynDNS.org<\/code> (which obviously was a smart decision since they now pretty much closed their free service) so I rolled my own…<\/p>\n

What you need is the following:<\/p>\n

    \n
  1. Host your domain yourself using the popular nameserver “Bind.”<\/li>\n
  2. Host a small CGI script that will tell you your external IP (or use one of the many free services available that do the same).<\/li>\n
  3. Run a machine within your LAN 24×7 which can detect changes of your external IP and update your hostname accordingly.<\/li>\n<\/ol>\n

    Step 1: Setup Bind for Dynamic DNS Update<\/h2>\n

    to do<\/p>\n

    Step 2: CGI Script<\/h2>\n

    The CGI script that needs to be deployed somewhere in the Internet to tell you your external IP is very simple and tiny and looks like this:<\/p>\n

    #!\/bin\/bash\r\necho \"Content-type: text\/plain\"\r\necho \"\"\r\necho \"$REMOTE_ADDR\"<\/pre>\n
    Step 3: External IP Probe<\/h2>\n
    Here’s the script that needs to run periodically on a machine (I use Ubuntu server) within your LAN (or on your Internet gateway, although if you have the means to run stuff on your gateway you could employ a more elegant, “proper” solution):<\/p>\n
    #!\/bin\/bash\r\nlockfile=\"\/run\/extip\"\r\nlockfile-check $lockfile\r\nif [ $? -eq 0 ]; then\r\n\u00a0\u00a0 \u00a0echo \"Locked, bailing out...\"\r\n\u00a0\u00a0 \u00a0exit 1\r\nfi\r\n\r\nlockfile-create $lockfile\r\nfilename=\"\/var\/lib\/extip.txt\"\r\nlogfile=\"\/var\/log\/extip.log\"\r\nkeyfile=\"\/root\/var\/lib\/dyndns\/Kmyhost.dyn.example.org.+163+56719.key\"\r\ncur_ip=`curl -s http:\/\/example.org\/cgi-bin\/myip.sh`\r\nprev_ip=`cat $filename`\r\nif [ $cur_ip != $prev_ip ]; then\r\n\u00a0\u00a0 \u00a0echo \"`date --rfc-3339=seconds` IP changed, old IP: $prev_ip, new IP: $cur_ip\" >>$logfile\r\n\u00a0\u00a0 \u00a0echo \"$cur_ip\" >$filename\r\n\u00a0\u00a0 \u00a0# Wait 5 sec to complete, force kill if nsupdate not done after 10 sec\r\n\u00a0\u00a0 \u00a0timeout -k 10s 5s nsupdate -k $keyfile -v<<EOF\r\nserver example.org\r\nzone dyn.example.org.\r\nupdate delete myhost.dyn.example.org. A\r\nupdate add myhost.dyn.example.org. 60 A $cur_ip\r\nsend\r\nEOF\r\nfi\r\nlockfile-remove $lockfile<\/pre>\n
    The above script — even though it’s pretty small — is not a quick’n’dirty hack, but even employs some sanity checks:<\/p>\n
      \n
    • It makes sure that only one<\/em> instance is running at any time, and<\/li>\n
    • it uses the timeout<\/code> command from the Linux coreutils<\/code> package to enforce that the nsupdate<\/code> command will be terminated if it takes longer than 10 s (e. g. due to network issues).<\/li>\n<\/ul>\n
      I run the above script once a minute as follows:<\/p>\n
      # cat \/etc\/cron.d\/extip \r\n* * * * * root \/usr\/local\/bin\/pubextip.sh<\/pre>\n
      That’s it!<\/p>\n
      Let me know what you think. Suggestions how to improve things are, as always, very welcome!<\/p>\n","protected":false},"excerpt":{"rendered":"
      I didn’t want to rely upon services like DynDNS.org (which obviously was a smart decision since they now pretty much closed their free service) so I rolled my own… What you need is the following: Host your domain yourself using the popular nameserver “Bind.” Host a small CGI script that will tell you your external […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[33],"tags":[81,93],"class_list":["post-482","post","type-post","status-publish","format-standard","hentry","category-linux-computers","tag-dynamic-dns","tag-dyndns"],"yoast_head":"\nHow to roll your own DynDNS... - Ralf's Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/bergs.biz\/blog\/2013\/08\/25\/how-to-roll-your-own-dyndns\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"How to roll your own DynDNS... - 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