Dynamic DNS Update Script for dynDNS behind NAT

Grateful thanks goes to "webasdf" on the forums (http://forum.mikrotik.com/viewtopic.php?p=171805#p171805) for this. I just edited it so that we can use the same identical script at every single one of our hotspots that are behind a Dynamic IP. The great ability of the original script by webasdf is that it uses DynDNS's html access method which means it will work behind a NAT'ed connection.

# Set needed variables
:local username "YourUsername"
:local password "YourPassword"
:local hostname "nohostset"
:global systemname [/system identity get name]

:if ($systemname  = "Site1" ) do= {
:set hostname "yourdomain1.dyndns.org"
}
:if ($systemname  = "Site2" ) do= {
:set hostname "yourdomain2.dyndns.org"
}
:if ($systemname  = "Site3" ) do= {
:set hostname "yourdomain3.dyndns.org"
}

:global dyndnsForce
:global previousIP

# print some debug info 
:log info ("UpdateDynDNS: username = $username")
:log info ("UpdateDynDNS: password = $password")
:log info ("UpdateDynDNS: hostname = $hostname")
:log info ("UpdateDynDNS: previousIP = $previousIP")

# get the current IP address from the internet (in case of double-nat)
/tool fetch mode=http address="checkip.dyndns.org" src-path="/" dst-path="/dyndns.checkip.html"
:local result [/file get dyndns.checkip.html contents]

# parse the current IP result
:local resultLen [:len $result]
:local startLoc [:find $result ": " -1]
:set startLoc ($startLoc + 2)
:local endLoc [:find $result "</body>" -1]
:local currentIP [:pick $result $startLoc $endLoc]
:log info "UpdateDynDNS: currentIP = $currentIP"

# Remove the # on next line to force an update every single time - useful for debugging, but you could end up getting blacklisted by DynDNS!
#:set dyndnsForce true

# Determine if dyndns update is needed
# more dyndns updater request details available at http://www.dyndns.com/developers/specs/syntax.html
:if (($currentIP != $previousIP) || ($dyndnsForce = true)) do={
    :set dyndnsForce false
    :set previousIP $currentIP
    /tool fetch user=$username password=$password mode=http address="members.dyndns.org" src- path="/nic/update?hostname=$hostname&myip=$currentIP" dst-path="/dyndns.txt"
    :local result [/file get dyndns.txt contents]
    :log info ("UpdateDynDNS: Dyndns update needed")
    :log info ("UpdateDynDNS: Dyndns Update Result: ".$result)
    :put ("Dyndns Update Result: ".$result)
} else={
    :log info ("UpdateDynDNS: No dyndns update needed")
}