[X-Unix] How to determine which network component is failing

[Wing Wong]

On 7/23/06, Charles Howse <chowse at charter.net> wrote:
> Hardware setup:
> ISP: Charter Communications, 2 megabit service
> Cable Modem: Motorola SB4200 Surfboard
> Router: Linksys Etherfast(r) Cable/DSL Router BEFSR41 V3 Firmware
> Version: 1.04.17
> Computers: 2 FreeBSD 6.1-RELEASE. 1 Mac OS X 10.4.7, 100 baseT
> ethernet connections on all
>
> This morning, I was offline, and just by accident decided to try and
> release and renew the ip address using the web interface of the router.
> BINGO!  Online again!
>
> Is this an indication that the router is not noticing that the lease
> has expired on my dhcp assigned ip address from the modem?  Or is it
> an indication that the modem is not renewing it's ip address?  Or is
> it something else?
>
> Can I tell the router to release / renew the ip address from a shell
> script?

Yes. I have a WRT54G Linksys router hooked up to my cablemodem and
this does indeed happen once in a while. Basically, when this happens,
one of two things happen:

1) the cablemodem/service has died and the cablemodem needs to be power-cycled.
2) the dhcp lease needs to be renewed.

Typically, I've found the lease to work fine by itself. But from time
to time, it doesn't. :/ The reasons for this vary, but I'm guessing
it's someone bouncing something over at the cable provider side and
the lease is just "forgotten", leaving your router with a useless
lease. So, hitting the release/renew will let you grab a new useful
lease, and back on the net.

I suppose you could script a lynx application to login to the web
interface of your Linksys router and perform a lease release/renew
once in while or when it is unable to access some remote server on the
internet.

Ie,

1) am I able to see the world?
** check google.com
** check msn.com
** check yourfavoritesite.com
If at least one is up, then you are essentially live and the other two
sites are coincidentally dead.

2) If I'm not up, let's run the scripted lynx session to perform a
release/renew of my IP address on the router.

3) Check output of the script. Did I actually get an IP address or am
I still stuck with 0.0.0.0? Wait a bit longer and run the scripted
lynx to read the DHCP address from the router again. If fail yet
again, scream for help!!

If you have some means to, you could script a powercycle of the cable
modem itself with an intelligent power socket. (serial control or over
net control) Just make sure you don't powercycle more frequently than
necessary. I've blown devices that way. ;) If you powercycle every
30seconds to every 5 minutes, it's amazing what 2 solid weeks of power
cycling will do to a device.


-- 
Wing Wong
wingedpower at gmail.com