[p2p-hackers] STUN server bindings

[David Barrett]

The STUN protocol indicates:

    A STUN server MUST be prepared to receive Binding Requests on four
    address/port combinations - (A1, P1), (A2, P1), (A1, P2), and (A2,
    P2).

Does this mean that a compliant STUN server must have two Ethernet 
cards, each configured with a different IP address?  Or is it possible 
for a single computer with a single Ethernet card to send and receive 
via two different IP addresses?  In general, how would such a thing be 
done on a Linux Fedora Core 2 server?

Alternatively, does this mean I need to have two separate computers 
working together, such that server A can receive a STUN request with the 
CHANGE_IP flag set, and then it can request that server B send the response?

-david