Wednesday, May 7, 2008

Dynamic DNS on a Cisco ADSL Router

Any new Cisco ADSL router in the 800 series should support dynamic DNS updates to a DDNS provider like

This particular example is for a Cisco 877 ADSL router.
NOTE: This particular config was done on a Cisco 877 ADSL / DSL router however its known to work on the Cisco 800 series DSL routers in general including the Cisco 827 Cisco 837 Cisco 877W as long as your Cisco IOS on the router supports the DDNS config

You might want to check the Cisco ADSL config guide too.

First off you are going to want to create an account with a DDNS Provider, this particular example uses but others should work in the same way or at least in a similar way. In this example the dns name we want is

OK lets go

Login to you router via console or telnet

Go into Enable mode
Then configure terminal (conf t)

ip domain name
ip name-server ip.ip.ip.ip
ip name-server ip.ip.ip.ip
ip ddns update method DynDNS
HTTP add # Note From HTTP to myip= is one line #
interval maximum 1 0 0 0

Breakdown of the Above Commands:

username:password This is the username and password of the account you created at the dyndns provider.
HINT: password issues seem to crop up with unless you use an alpha-numeric combination pass123 for instance also shy away from pass!@# at least at the time of this How-To anyway. You can leave this as it is if you are using HINT the ? after this might cause problems
where the Cisco router thinks that you are asking for help you can escape this by pressing CTRL
and V at the same time then ?

system=dyndns There are 3 Options here dyndns is the one to use if you are using one of the default domains.

hostname= The hostname you are updating in this case

myip= Leave this blank the dyndns site will determine what IP your ISP has issued to you

interval maximum This is the Maximum Interval in time that will pass before your router sends your DDNS provider an update. For
testing purposes you can use interval maximum 0 0 5 0 (every 5 minutes) the First 0 is Days 0 - 365 the second 0 is
Hours 0 - 23 the third 0 is minutes 0 - 59 and the last one is for seconds 0 - 59. Once you have determined that the
DDNS Config is working I would suggest that you change it to 0 1 0 0 (once a day in other words) if for some reason
your IP Address is changed before that 24 hour period your router will automatically update your DDNS Provider

interface Dialer1
ip ddns update hostname
ip ddns update DynDNS host

interface Vlan1
ip ddns update hostname
ip ddns update DynDNS host

Once you have that all added write the config, then enable dedugging turn on terminal monitor

debugging ip ddns update
term mon

I have noticed that to get the DDNS kick started that its best to shut the dialer interface and then un-shut it. As soon as you do that you start seeing debugging info on the terminal window.

If things work out you should see something like this happening

Example IP's <-- IP assigned to the router by the ISP <-- The IP of the the DDNS provider's HTTP page that your router is logging into to update. 00:04:35:%DHCP-6-ADDRESS_ASSIGN: Interface Ethernet1 assigned DHCP address,
mask, hostname

00:04:35: DYNDNSUPD: Adding DNS mapping for <=> server

00:04:35: DYNDNSUPD: Sleeping for 3 seconds waiting for interface Ethernet1 configuration
to settle

00:04:38: HTTPDNS: Update add called for <=>

00:04:38: HTTPDNS: Update called for <=>

00:04:38: HTTPDNS: init

00:04:38: HTTPDNSUPD: Session ID = 0x7

00:04:38: HTTPDNSUPD: URL =

00:04:38: HTTPDNSUPD: Sending request

00:04:40: HTTPDNSUPD: Response for update <=>



00:04:40: HTTPDNSUPD: DATA END, Status is Response data received, successfully

00:04:40: HTTPDNSUPD: Call returned SUCCESS for update <=>

00:04:40: HTTPDNSUPD: Freeing response

00:04:40: DYNDNSUPD: Another update completed (outstanding=0, total=0)

00:04:40: HTTPDNSUPD: Clearing all session 7 info

Now if all the above things happened you should by able to do a dig or nslookup for your host name (

$ dig

in the answer section you should see somehting like this
; IN A


or you can do an nslookup

Non-authoritative answer:

If you then reboot your router or even shut and un-shut your Dialer 1 Interface your ISP will Probably issue you will another IP if thats the case give it a few seconds and a Dig should give you another IP associated to the hostname.
Remember to change the interval maximum once you have determined that it does work For other DDNS Providers most things should stay the same except for the "add http:username:password........" thing and of course the "ip ddns update DynDNS host xxxxx " and "ip ddns update hostname xxxxx"

Here are some examples of others







1 comment:

fishandchips said... does not exist. I modified it to and it all came good.

Thanks for all the help.

Joe's Store