[PLUG] PLUG Digest, Vol 89, Issue 5

[Russell Senior]

>>>>> "Mike" == Mike Connors <mconnors1 at gmail.com> writes:

Russell> If you are running a DHCP client, then when your dynamic
Russell> ipaddr changes your ping will continue to succeed and you
Russell> won't be able to tell that anything has changed.  The better
Russell> answer is to take control of the software running on the
Russell> gateway and just have a script *there* watch for a ipaddr
Russell> change.  OpenWrt FTW!

Mike> If the assigned DHCP ip address does change, the ping should
Mike> fail because the originally assigned DHCP ip address will be
Mike> pulled back into the pool and very likely not reassigned within
Mike> a few minutes. DLS modems are not requesting new IP addresses at
Mike> the rate you would expect laptops connecting to a WIFI AP at an
Mike> airport.

Ah, you mean to ping the last known public ipaddr of the DSL modem.
That wasn't clear.


[ Internal host ] --- [ DSL ] ---- [ ISP ] --- [ whatsmyip.org ]

So, your suggestion is to have a script on the internal host that
every hour or so queries whatsmyip.org and every
<much-more-frequently> pings the ipaddr that query returns.  If the
ping fails significantly, re-query whatsmyip.org immediately.  If
ipaddr has changed, fire off the DNS change.


-- 
Russell Senior, President
russell at personaltelco.net