This document will review procedures for using Ascend Pipeline 50, Pipeline 75 and Pipeline 130 routers to obtain IP addresses dynamically from a Network Access Server (NAS). (The Pipeline 50, 75 and 130 are the ONLY Ascend routers that support this "NAT for a LAN" feature. The Pipeline 25-Px does support NAT, but only for a single workstation.) This technical note assumes your ISDN line is configured and working properly. Information in this document is excerpted from the appropriate incremental software release notes, located at ftp://ftp.ascend.com/pub/Software-Releases/Pipeline /Incremental/Release-5.0Ai16/doc/rp50ai.pdf and experience.
Single Workstation Example:
The following example, for setting up NAT to a single workstation, is a typical setup for a connection to an ISP.
The Pipeline MUST be on software 5.0A or better. Software upgrades are available online at ftp://ftp.ascend.com/pub/Software-Releases/Pipeline/ . You must have an account with your ISP that is set up to dynamically assign you an IP address.
How it works:
When the Pipeline first connects to the NAS, it receives an initial IP address via PPP negotiation. The Pipeline then builds a lookup table that matches the workstation's bogus address with the registered address that the NAS assigns. The Pipeline re-addresses packets destined for your workstation (i.e., destined to the registered address) with the bogus address it actually has. This translation is transparent both to the workstation and to devices on the WAN.
Multiple Workstation Example:
You must satisfy a few additional requirements before using NAT for a LAN of multiple workstations. The setup for the Pipeline is exactly the same as it is for single-workstation NAT. The feature required "single-to-many NAT" is incorporated only in software release 5.0Ai10 and later.
Configure the Pipeline exactly as you would for a single-workstation application.
Each workstation must have a unique IP address on the same logical network as the Pipeline. For example, if the Pipeline has an IP address of 126.96.36.199/24 and you have three workstations on the same Ethernet segment, you could address the workstations as 188.8.131.52/24, .202/24, and .203/24.
When NAT Routing=Yes, the Pipeline 50 or 75 is NOT accessible from the WAN (i.e., you cannot telnet into it from the Internet). It is still accessible from the local network (using the private address).
Be aware that, if the ISDN connection drops (e.g., because of an idle time-out), there is no guarantee that upon reconnection you will get the same IP address assigned. For example, if you are using a web browser and the connection drops because you go idle, if you then click on a link, you might get an error message because you now have a different IP address.
Be certain that Ignore Def Rt=Yes (on the Pipeline, under Ethernet->Mod Config->Ether options...) to prevent the NAT default route from being overwritten.
Certain applications, like some UDP-based Internet game and chat client programs, will work unreliably or not at all when using NAT because they report their bogus, private IP address to the server instead of the "correct" dynamically assigned address.
There is a command in debug mode that will tell you the address assigned by the NAS. Enter the command "napt" in debug mode and you will see the address assigned by the NAS.
For more information on additional NAT features such as static port mappings and NAT over Frame Relay, check the release notes for 5.0A incremental releases (available at the link referenced at the beginning of this document).