3com 3C840 Guía Del Usuario
Port Address Translation (PAT)
C-5
Doing this provides a firewall and hides the private local network from
the outside world.
the outside world.
Figure C–2 PAT Example
Dynamic PAT
When a local PC sends a packet destined for the WAN, the OfficeConnect
Remote 840 puts its source IP address and a port number into an address
translation table. The port number is also placed into the data packet.
Remote 840 puts its source IP address and a port number into an address
translation table. The port number is also placed into the data packet.
An additional change is made to the packet: the original (private) source
IP is replaced by the OfficeConnect Remote 840 WAN IP address. Then
the packet is sent to the WAN.
IP is replaced by the OfficeConnect Remote 840 WAN IP address. Then
the packet is sent to the WAN.
The reply will contain the OfficeConnect Remote 840 WAN IP address
and port number. The port number is used to search the address
translation table for the original private IP address.
and port number. The port number is used to search the address
translation table for the original private IP address.
The original IP address is then put in a reply and sent to the Ethernet.
This method requires initiating incoming packets from the LAN. Packets
from the WAN are rejected unless they currently have a port number in
the table.
from the WAN are rejected unless they currently have a port number in
the table.
Static PAT
Static PAT operates like Dynamic PAT except you may add entries to the
address translation table and specify which port numbers to map to
which private IP addresses. This allows controlled access by the outside
address translation table and specify which port numbers to map to
which private IP addresses. This allows controlled access by the outside
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