[ale] Strange Linux networking issue

[Derek Atkins]

Hi,

On Mon, April 19, 2021 2:17 pm, Jim Kinney wrote:
> ???
> Two hosts directly connected with neither switch nor cross-over cable.
> ???
>
> Sounds like the two nics auto-negotiated themselves to death.

That was certainly one of my theories.  (NB: I'm helping someone else
debug this, it's not my design).  The strange part was that it was working
fine for a week or two before kicking the bucket.

> To test, stop networking on boxA, rmmod nic modules, insmod nic modules,
> start networking. If ping runs a bit after that, disable autoconfig.

We've been trying to do non-destructive edits at the moment to debug, but
yes, this is a good option to attempt to "get it back online".

-derek

> On April 19, 2021 1:06:07 PM EDT, Derek Atkins via Ale <ale at ale.org>
> wrote:
>>HI.
>>
>>I'm having a strange networking issue between two AWOW devices running
>>Linux that stopped talking to each other.  The devices are configured
>>as
>>below:
>>
>>--(a)[Box 1](b) ----- (c)[Box 2](d)--
>>
>>Where:
>>(a) is 172.16.5.0/16
>>(b) is 172.16.5.1/16
>>(c) is 172.16.7.100/16
>>(d) is 172.16.7.0/16
>>
>>The (b)/(c) link is a direct link between the devices, not a crossover
>>cable, and no switch.
>>
>>The two devices were talking fine for a while and then all of a sudden
>>they stopped.  Now that won't talk at all.  When truing to ping .7.100
>>from Box 1, it sends out ARPs but there is no ARP response from Box 2.
>>Similarly, on Box 2 trying to ping .5.1 results in no ARP responses.
>>
>>Both devices show the (b)/(c) link as up.  Running ethtool shows the
>>link
>>is detected.  However arp -an shows an incomplete response (no
>>surprise).
>>
>>The dmesg output doesn't show anything.
>>
>>I am at a loss. I don't understand how or why the two devices would
>>stop
>>talking, and why neither will pick it up again.
>>
>>Any suggestions for where to look or how else to debug this?
>>
>>Thanks,
>>
>>-derek
>>
>>--
>>       Derek Atkins                 617-623-3745
>>       derek at ihtfp.com             www.ihtfp.com
>>       Computer and Internet Security Consultant
>>
>>_______________________________________________
>>Ale mailing list
>>Ale at ale.org
>>https://mail.ale.org/mailman/listinfo/ale
>>See JOBS, ANNOUNCE and SCHOOLS lists at
>>http://mail.ale.org/mailman/listinfo
>
> --
> Computers amplify human error
> Super computers are really cool


-- 
       Derek Atkins                 617-623-3745
       derek at ihtfp.com             www.ihtfp.com
       Computer and Internet Security Consultant