881 router does not automatically reconnect after ISP drop

[dyfodolbvba]

We are having an issue with some 881 cable routers.

They are connected to the ISP cable modem on the WAN port.

Every so often, the ISP drops their signal for a couple of seconds, after which the internet connection is lost.

We tried rebooting the cable modem, no result.

The only thing that helps is to reboot the 881 router itself, after which internet access is restored.

As the WAN port is set to DHCP client, it seems odd that the connection isn't automatically brought up once the ISP is back online.

We are obviously missing some crucial config to make the router reconnect automatically.

What could cause this and how to resolve it ?  Could anyone assist us in this ?

Thanks.

[cadet alain]

Hi,

if the router interface is still up/up then it won't try to renew its address before the renewal timer T1 which is by default  1/2 lease time and then 1/2 of remaining lease time= 75% and then still 1/2= 87.5%

You could use IP sla to ping ISP default gateway and if unsuccessful shut/no shut the interface or renew address with a TCL script or EEM applet.

Regards.

Alain.

[dyfodolbvba]

Thanks,  this looks like an interesting line of thought.

A couple of questions though...

How frequently could we run the ping command without overburdening the router and distracting it from it's core business ?

TCL and EEM are unchartered territory for me, any pointers as to good places to start for finding information on how to do this ?

Also, I am still confused as to why the connection goes away although we get the same IP address after the reboot ...  something to do with the ISP's routing tables perhaps ?

Many thanks,

G.

[Edison Ortiz]

The router's interface never goes down so it retains its IP address from the ISP but it seems when the internet goes down the ISP requires a new IP address from you. The router's DHCP lease may last days so it won't request a new IP address. The only way to force the router to request a new IP address w/o rebooting it is to shutdown the port connected to the cable modem and then perform a 'no shutdown'.

[dyfodolbvba]

The ISP always provides the same IP adres through their DHCP server (their way of providing fixed adres), so would your logic still apply ?

[cadet alain]

Hi,

concerning the router not reclaiming a new address if the interface is up, yes the reasoning is still good.

Alain.