[Wlug] ISP/Router/Modem Ethernet communications

[John Stoffel]

kstratton> I just went through some painful debug session(s) with my
kstratton> ISP.  For some reason, after forcing 10 base T half duplex
kstratton> through my windows box directly to my modem (I do not
kstratton> expect ISPs to support linux),everything suddenly worked
kstratton> (after reconnection and re-enabling of course).

Can you give more details on the cable modem box you're using and the
PC as well?  Such as what network card in the PC you are using? 

kstratton> How often does this kind of thing happen?  I have seen this
kstratton> kind of thing before only once before, and I was using an
kstratton> old hub that only supported 10 base T, not a home router
kstratton> that is supposed to autodetect the port type.  I remember
kstratton> that the modem only supports 10 base T, but I am not 100%
kstratton> certain.

Sun and Cisco were notirious for having problems figuring our
autonegotiation on the Sun hme (Happy Meal Ethernet) cards.  They'd
end up 100Full on one side and 100 Half Duplex on the other.  It would
work, just very slowly...

kstratton> Does anybody have an explanation of what most likely
kstratton> happened?  Do not hesitate to skimp on technical details or
kstratton> references if is convenient.  I desperately want to
kstratton> understand what happened.  --
  
Something didn't autonegotiate properly.  Did you try powering off
both devices and then powering them on starting with the cable box?

Also, alot of Cable Companies lock the cable box to the first MAC
(ethernet hardware address) they see coming over the link.  So if you
boot up with a PC, and then try to move to something else like a NAT
box or a linux box acting as a NAT box, things can go wonky.  

Usually a hard reset of the Cablemodem will do the trick, but
sometimes you need to contact the ISP and ask them to reset it for
you.

In your case, it really sounds like a problem with Autonegotiation.
Some devices just don't do a good job, esp older equipment from before
the Gigabit ethernet stage.  

Just to expand on Frank's email, the people who designed the Gigiabit
Ethernet standard over Copper (802.xxx I can't remember) saw all the
problems with the 100/10 devices and autonegotiation and explicity
made AutoNeg part of the spec in a very well detailed way, so that
these problems won't happen again.  As a matter of fact, Gigabit ports
are much smarter and don't require crossover cables either, you can
just plug them into back to back, they figure out what's going on
automatically and adjust.  

The joys of big ASICs!  

John