i stuck recently on strange problem with SG580. My i-net provider has a carier network to my router e.g. 83.231.x.x and i have a pool of real IP addresses e.g. 64.73.x.x which are assigned to 5 machines. A week ago i was able to access or ping these machines from "outside" but now it is not possible. The unit allows me to connect only to port B e.g. 83.231.x.x . I updated the router with the latest firmware but it did not help and then i got back to the initial firmware 3.1.5u4 .Do you have any idea what could be the problem ?
it sounds like an arp issue.
if you use a packet sniffer such as available under system -> diagnostics -> packet capture
or from the command line ( as an example to looks for pings )
tcpdump -e -n -i eth1ip proto 1
does the incoming packets for 83.231.x.x have the same destination mac address as the 64.73.x.x packets ?