[Cialug] Basic Networking ARP and Routers

[Nick Graber]

I checked the settings on the Schneider PLC
IP: 10.1.88.250
SNM: 255.255.255.0
GW : 10.1.88.254



On Thu, Jul 24, 2014 at 3:16 PM, Zachary Kotlarek <zach at kotlarek.com> wrote:

>
> On Jul 24, 2014, at 1:04 PM, Nick Graber <nick at graber.me> wrote:
>
> > The Schneider PLC is using ARP outside of it's subnet and expecting a
> reply
> > from the router with it's MAC to make a connection with the AB PLC I
> think.
> > Should the router replay to such and inquiry or should the PLC do an ARP
> > for the Default Gateway then send the packet to the Default Gateway?  It
> > appears it is using ARP to try and discover the router that controls
> > 172.20.87.255 and I'm not sure that is possible.
>
>
> It looks like the Schneider thinks that 172.20.87.235 is link-local.
> Otherwise it would ARP for the router, not the destination.
>
> My guess is the Schneider is not configured to use the router, either
> because the subnet information it has is wrong (maybe set to 0.0.0.0) or
> because it does not support IP routing (which sometimes happens on dumb
> equipment even though it pretends to speak IP).
>
> It is possible to bridge the two networks in such a way that this works,
> but I’d start by ensuring that 172.20.87.235 doesn’t match the subnet on
> the Schneider.
>
>         Zach
>
>
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