User`s guide

IP Address Management
Network Address Translation (NAT) for a LAN
3-24 Preliminary January 30, 1998 Pipeline User’s Guide
Incoming connection address translation
For incoming calls, the Pipeline can perform NAT for multiple hosts on the local
network using its own IP address. The Pipeline routes incoming packets for up to
10 different TCP or UDP ports to specific servers on the local network.
Translations between the local network and the Internet or remote network are
static and need to be preconfigured. You need to define a list of local servers and
the UDP and TCP ports each would handle. You can also define a local default
server that handles UDP and TCP ports not listed.
For example, you can configure the Pipeline to route all incoming packets for
TCP port 80—the standard port for HTTP—to port 80 of a World Wide Web
server on the local network. The port you route to does not have to be the same as
the port specified in the incoming packets. For example, you can route all packets
for TCP port 119, the well known port for Network News Transfer Protocol, to
port 1119 on a Usenet News server on the local network. You can also specify a
default server that receives any packets that aren’t sent to one of the routed ports.
If you don’t specify any routed ports but do specify a default server, the default
server receives all packets from the remote network that are sent to the Pipeline.
When you configure the Pipeline to route incoming packets for a particular TCP
or UDP port to a specific server on the local network, multiple hosts on the
remote network can connect to the server at the same time. The number of
connections is limited by the size of the translation table.
Note:
NAT automatically turns RIP off, so the address of the Pipeline is not
propagated to the Internet or remote networks.
Translation table size
NAT has an internal translation table limited to 500 addresses. A translation table
entry represents one TCP or UDP connection.
Note:
A single application can generate many TCP and UDP connections.
The translation table entries are freed based on the following timeouts:
• Non-DNS UDP translations timeout after 5 minutes.
• DNS times out in one minute.
• TCP translations time out after 24 hours.