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Thread: Dynamic DNS

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    Master Control Freak RussM's Avatar
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    Dynamic DNS

    Dynamic DNS (aka DDNS)

    Before we delve into the specifics of DDNS, let’s talk about DNS to get some background info.

    So what is DNS? The Domain Name System (DNS) is a standard method for resolving Internet hostnames into IP addresses. Computers/servers/printers/network cameras, etc. all communicate using an IP address, like 75.118.48.51. This is not user-friendly - us humans have a hard time remembering strings of numbers like that. http://forum.neptunesystems.com is undeniably much easier for us to remember and use than http://50.62.150.37.

    DNS uses servers "in the cloud" to maintain a huge distributed database of static DNS records, mapping a hostname like forum.neptunesystems.com to its actual IP address. When you use your web browser and try to go to a web address (also called a Uniform Resource Locator or URL) like www.google.com, your computer does a DNS query to the Internet, essentially asking "What is the IP address for www.google.com?" A DNS server (usually your ISP’s DNS server) will attempt to look it up in its own DNS database. If it finds records for the requested URL, it replies with the equiavalent of "The IP address of www.google.com is 97.74.27.1"; your computer then establishes communications to Google using that IP address. If the ISP’s DNS server doesn’t know the IP address, it forwards your query out to other DNS servers, and when it learns the IP address, it relies back to you. All this happens in the blink of an eye. One of the key things about standard DNS is that it is static info, generally updated world-wide once a day - it is intended for mapping hostnames to static IP addresses. For example, forum.neptunesystems.com’s IP address is hard-coded (static) and doesn’t change, so normal DNS is perfectly fine for things like commercial web sites.

    Dynamic DNS is a way to utilize DNS to map hostnames to IP addresses which change on a regular basis - such as the public IP address dynamically assigned to almost all of us by our ISP. My IP address, for example, is currently assigned an address of 72.199.140.xxx. I’ve had this address for several months, but it CAN change at any time. The public IP addresses assigned to residential subscribers by cable companies, and for services like ATT’s U-Verse and Verizon’s FIOS tend to get changed very infrequently (I had my previous IP address from Cox for over 2 years). But, those subscribers with standard DSL can get new IP addresses much more frequently - it is not unusual for DSL subscribers to get a new IP address every few days or when the router/DSL modem gets restarted. This dynamic IP address allocation is a nuisance when you are trying to access your Apex or AC3 or reefcam remotely; if you are away from home, and your public IP address changes, you won’t be able to access that device remotely until you get home and figure out that your public IP address changed and identify the new IP address. This is where Dynamic DNS really shines.

    Not only does DDNS provide us with human-friendly hostnames (as does standard DNS), it also provides a mechanism to determine if your public IP address gets changed and automatically updating a DDNS hostname like ‘russm-apex.home-ip.net’ when that happens.

    A side note: There is a popular misconception that using Dynamic DNS gives you a static IP address - this is not true. DDNS merely gives the appearance of having a static IP address.

    There are at least 5 different variants of DDNS, but only three are typically used on the Internet. One of those is an Apple-proprietary method called Wide-Area Bonjour, but it is not really applicable to us for accessing our controller or reefcam remotely; another method using a protocol called TSIG is far too complicated for everyone but IT technogeeks. I will not discuss either of these methods here.

    The other common method - by far the most widely used - is available through the use of online DDNS providers. There are quite a few DDNS provides out there: http://Dyn.com (aka http://dyndns.org), http://no-ip.com, http://freedns.afraid.org, http://zoneedit.com, etc. Some offer free accounts; other charge widely-varying fees. Some router and network camera manufacturers also offer free DDNS services for their customers. D-Link and Foscam are two such companies. Dyn.com is probably the largest, best, and most widely-supported by router/camera manufacturers. To use one of these services, you must sign up for an account on the provider’s web site. I’ll will discuss the selection of a DDNS provider a bit later.

    As mentioned above, one of the necessary components of DDNS is a mechanism to automatically detect a change in your public IP address and update the hostname record with the new IP address as needed. There are three common means of updating DDNS:


    • Your router may have DDNS support built-in
    • Your network camera/reefcam may have DDNS support built-in
    • You can download and install a small software package from the DDNS provider to provide the IP change detection and update function; this program must run in the background all of the time.


    Using the DDNS support in your router is by far the better option. Your router, for example, is typically on 7/24/365, so it can constantly monitor the public IP address assigned by your ISP, and can detect that change instantaneously and update your DDNS account as needed. Embedded DDNS updater support for one or more DDNS providers is available in most routers from Cisco/Linksys, D-Link, Asus, Netgear, Belkin, etc. There are two notable exceptions: Apple Airport routers and ATT-supplied 2Wire and Pace brand routers do not support any 3rd party DDNS services. Using DDNS support in a network camera is almost as good as using the router. Most if not all current cameras from D-Link, Foscam, Cisco/Linksys, Axis, etc. also have embedded DDNS support. An important note: if you have two routers daisy-chained (such as a D-Link router behind a Verizon FIOS router, you usually cannot use the DDNS feature in the D-Link - most router's DDNS support require the router to be directly connected to the Internet.

    Using a software updater client has three significant drawbacks:
    1. To work properly, the computer on which it is installed needs to be on and connected to the Internet 7/24; it cannot detect a change in your public IP address if it isn’t on!
    2. Software updaters will only check periodically to see it the public IP address has changed; usually, at 10- or 15-minute intervals.
    3. A software updater will update your DDNS account using the public IP address of wherever the computer is – this a big issue if you use a portable computer. If you take your notebook (which is running a DDNS client in the background) to work/school/Starbucks/McDonald’s/Grandma’s house/etc., your DDNS account will be automatically be updated with the public IP address of that particular place - and that’s BAD, because your Apex/AC3/camera isn’t there!


    So, I’ll say it again: You should ALWAYS use your router or network camera to update a DDNS account if possible.

    Selecting a Dynamic DNS service


    1. When you pick a DDNS provider, you should pick one which is supported by your router or camera if that device has a DDNS update feature. If your router or camera has such support for only one provider, your choice is clear: use that DDNS service.
    2. If your router/camera has options for more than one DDNS service, you can take your pick of those supported. D-Link’s DCS-9xx, DCS-2xxx, and DCS-5xxx series of cameras, for example, support dyn.com (dyndns.org) and D-Link’s own free DDNS service, dlinkddns.com (which is actually run by dyn.com).
    3. If your router and camera both have DDNS support, in general it will be better to use the router. Although in some cases, there may be added benefits to using the camera manufacturer’s DDNS service over a 3rd-party DDNS.
    4. There is absolutely no need for 99% of us to use a paid DDNS service. A free account is just fine.


    A few other points


    • Of all of the various independent/3rd-party DDNS providers, Dyn.com (aka dyndns.org) is my favorite, and the one I usually recommend; I’ve been a subscriber for over a decade, and it has been a flawless and 100% reliable service. But, they no longer offer free accounts. It currently costs $25/year. I personally feel that the cost is worthwhile, and in the grand scheme of things, insignificant. But I fully understand that many will want to use a free service.
    • You only need one DDNS hostname even if you have multiple devices which you need to access remotely, such as two Apexes or an Apex and a camera. When you configure port forwarding to each device, the public-side port number is what’s used to allow the router to determine which device to forward traffic to. So one hostname is all you need; for example I would use http://russm.home-ip.com:8888 for my Apex, and http://russm.home-ip.com:9999 for my camera. Of course, you can have multiple hostnames if you so desire, but that is absolutely unnecessary.
    • You must use only ONE method of updating a given DNS account. Do NOT, for example, use your router AND a software client concurrently to update the same dyndns.org (or other DDNS provider) account.
    • The AC3 and Apex use (standard) DNS to find the IP address of the configured mail server to use for sending email alerts. The controllers do not use DNS for anything else. The controllers do not use dynamic DNS at all. Dynamic DNS is used only by you for accessing the controller (or camera) remotely across the Internet.
    Last edited by RussM; 06-18-2013 at 12:57.

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