[ale] Strange Linux networking issue

Phil Turmel philip at turmel.org
Tue Apr 20 08:52:55 EDT 2021

I would not expect that layout to work except by chance.  With those 
subnet masks, each box is free to send any packet to 172.16.x.y out 
either interface at any time.  Specifying an interface for ping won't 
prevent the other box from replying out the wrong interface.

To be reliable, (b) and (c) need to be in the same subnet, and (a) and 
(d) need to be in different subnets.   Not necessarily different subnets 
from each other, but definitely different from the b/c subnet.

On 4/19/21 1:06 PM, Derek Atkins via Ale 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
> (b) is
> (c) is
> (d) is
> 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

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