[ale] Strange Linux networking issue

[Raj Wurttemberg]

Quick, simple and cheap analysis idea.  Put a cheap gig-switch in-between
(b) and (c).  

I'm sure we all have  a few 5 or 8 port switches laying around. Haha!

/Raj

> -----Original Message-----
> From: Ale <ale-bounces at ale.org> On Behalf Of Derek Atkins via Ale
> Sent: Monday, April 19, 2021 1:06 PM
> To: ale at ale.org
> Cc: Derek Atkins <derek at ihtfp.com>
> Subject: [ale] Strange Linux networking issue
> 
> 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