Motorola SBG6580 can't configure DDNS

Motorola support sez:

1. Launch a web browser, such as Internet Explorer, Firefox, or Safari. Enter http://192.168.0.1 into the address box.
2. Enter admin in the Username field
3. Enter motorola in the Password field. (If not changed)
4. Click the Login button. The Status Connection page appears.
5. Click the Firewall link from the top tabs. The Firewall Web Content page appears.
6. Under Web Features, uncheck Firewall Protection and click the Apply button.
7. Click the Basic link from the top tabs. Click the DDNS link from the left-hand column.
8. On the DDNS page, select Disabled for the DDNS service and click the Apply button.
9. On the same DDNS page, reenable the service by selecting http://www.DynDNS.org and click the Apply button.
10. Wait 2 -3 minutes and refresh the current page by pressing F5 or the refresh button from the web browser.
11. The status will change to "The update was successful". 12 Click the Firewall link from the top tab.
12. Reenable the Firewall Protection and click the Apply button.

This seems to work. At least, I was able to successfully complete the configuration for DynDNS.{org,com}. I guess I'll have to wait until my ISP next changes the IP address to be sure, but it seems OK.

I found similar directions elsewhere on the net, with one key exception: the instructions above say to reenable the Firewall Protection. That seems pretty important! I thought the other sites were saying that I had to leave Firewall off permanently to use DynDNS. Looks like that's not so. Big relief!

I assume you're entering your full DynDNS hostname (myhost.example.com) and username (not email address) from the DynDNS site? Also, if your password contains more than just standard ASCII letters and numbers, or is over 8 characters long that may also be the problem - some embedded clients are known to have short (undocumented) limits on the password.

I would suggest you check to see if there's a firmware update available. If not it sounds like it is another device with a broken update client.

It sounds then like the built in update client is broken in some way. You'll need to use some other device, or a software client.

The DDNS client on the SBG6580 is, indeed, broken if the firewall is turned on, at least for software versions < 3.3 (verified with Motorola Support).

The instructions for turning the firewall off does work for getting the router's DDNS function to update successfully. However, if you turn the firewall back on, no updates to your IP will register.

Leaving the firewall off on the SBG6580 only means that "SPI" or Stateful Packet Inspection is disabled. NAT still functions normally. NAT itself provides good security, as packets that originate on the WAN that are not responses to traffic initiated behind the router are still rejected, as the router will not know where to map the WAN packets to a device on the LAN, and will simply discard the packet. Again, this was verified with Motorola Support.

Bottom line is that, if you need the DDNS update capability built into the router, leaving the firewall disabled in the SBG6580 is probably safe, and should result in faster throughput as the router does not need to track the sessions associated with each packet.