[Cialug] Basic Networking ARP and Routers

[Nick Graber]

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.


Wan{
    Schneider PLC [10.88.1.250]
    Sixnet Router WAN [10.88.1.254]
}

Lan{
    Sixnet Router LAN [172.20.87.1]
    AllenBradly PLC [172.20.87.235]
}


Example Packet Capture:

https://www.dropbox.com/s/s75m34lhu47y9rr/IOScanner.pcapng

Thanks,
Nick Graber