[geeks] Kronos timeclocks

[Dan Sikorski]

I'm overdue for a quick message to let everyone know what i figured out 
for my kronos timeclock issue.

As Ian suggested, the reason why they worked with the cisco routers is 
because of proxy-arp, so i looked into how to get proxy-arp enabled on 
the procurve switch that is doing the routing between those two 
networks.   It was an easy thing to do, but i still had the exact same 
problem that i had before enabling it.  (later i found out that 
proxy-arp is effectively turned on whenever the switch is doing routing, 
even if it is not explicitly enabled.)  After spending some time with a 
packet sniffer, it turns out that the timeclock never actually makes an 
arp request for the address of the time collection PC that it is trying 
to talk to.  What it does instead is just use the MAC address from the 
source field in the header of the packet recieved from the time 
collection PC.  This works fine for the cisco router, because when it 
sends out routed packets, it uses it's own normal MAC address as the 
source address of all packets sent out.   The HP procurve switch 
however, does not send out routed packets from it's MAC address that is 
used for recieveing data, instead it will use a different address which 
it will not recieve data on.  So when the clock tried to send data back 
to that MAC address, it gets nowhere.

So, in the end, i ended up replacing the hub that the timeclocks were 
plugged into with a managed switch, and set the timeclocks up on the 
same vlan as the time collection PC. 

    -Dan Sikorski