User`s guide

IP Address Management
Network Address Translation (NAT) for a LAN
Pipeline User’s Guide Preliminary January 30, 1998 3-25
The translation table entries are reused as long as packets are seen that match an
entry. All are freed (expired) when a connection disconnects. For Nailed
connections, the connection is designed not to disconnect.
Multiple-address NAT
Multiple-address NAT can be performed when translating addresses for more
than one host on the local network. To do this, the Pipeline borrows an official IP
address for each host from a Dynamic Host Configuration Protocol (DHCP)
server on the remote network or accessible from the remote network.
The advantages of multiple-address NAT are that hosts on the remote network
can connect to specific hosts on the local network, not just specific services such
as Web or FTP service, but only if the DHCP server is configured to assign the
same address whenever a particular local host requests an address. Also, network
service providers might require multiple-address NAT for networks with more
than one host.
When you use multiple-address NAT, hosts on the remote network can connect to
any of the official IP addresses that the Pipeline borrows from the DHCP server.
If the local network must have more than one IP address that is visible to the
remote network, you must use multiple-address NAT. If hosts on the remote
network need to connect to a specific host on the local network, you can
configure the DHCP server to always assign the same address when that local
host requests an address.
When multiple-address NAT is enabled, the Pipeline attempts to perform IP
address translation on all packets received. (It cannot distinguish between official
and private addresses.)
The Pipeline acts as a DHCP client on behalf of all hosts on the LAN and relies
on a DHCP server to provide addresses suitable for the remote network from its
IP address pool. On the local network, the Pipeline and the hosts all have “local”
addresses on the same network that are only used for local communication
between the hosts and the Pipeline over the Ethernet.
When the first host on the LAN requests access to the remote network, the
Pipeline gets this address through PPP negotiation. When subsequent hosts
request access to the remote network, the Pipeline asks for an IP address from the
DHCP server using a DHCP request packet. The server then sends an address to