D-2 User’s Reference Guide

When the Netopia R2121 establishes a connection over its WAN interface with another router it uses the Point to Point Protocol (PPP). Within PPP there is a Network Control Protocol (NCP) called Internet Protocol Control Protocol (IPCP) which handles the negotiation of IP addresses between the two routers, in this case the Netopia R2121 at the customer site above and the Router at the Internet Service Provider (ISP).

If the Netopia R2121 calls the Router at the ISP with NAT disabled, the Netopia negotiates its LAN interface address (as specified in IP Setup within the Netopia R2121's console) with the Router at the ISP through IPCP and then sets up routing. From the previous diagram you can see that the address for the Netopia R2121 is 192.168.5.1 and the address of the Router at the ISP is 200.1.1.1. Assuming that the addresses negotiated by the routers are valid and unique for the Internet, the Netopia R2121 and the hosts on its LAN would be able to access the Internet.

If the Netopia R2121 calls the Router at the ISP with NAT enabled, instead of negotiating the LAN interface address the Netopia R2121 suggests the address 0.0.0.0 through IPCP. When the Router at the ISP sees this all-zeros IPCP request, the Router can either pull a free dynamic IP address from its pool and assign it to the Netopia R2121’s WAN interface or, if configured to do so, match the Netopia R2121's incoming connection profile and assign a pre-configured static IP address to the Netopia R2121's WAN interface.

From the previous diagram, you can see that the IP address assigned to the Netopia R2121's WAN interface is 200.1.1.40, while the IP address assigned to the LAN interface remains the same. The LAN interface address 192.168.5.1 is thus hidden from the ISP and the Internet, and the Netopia R2121 only has a single valid IP presence on the Internet. The LAN interface IP address for the Netopia R2121 can be any IP address, however it is recommended that you use the IANA specified 192.168.X.X Class C address range which is used for networks not attached to the Internet. This address range is described in RFC 1597.

The dynamic IP address acquisition on the WAN interface of the Netopia R2121 is one of several features of NAT. Another is the mapping of locally assigned IP addresses to the single globally unique IP address acquired by the Netopia R2121 on its WAN interface. NAT employs several things to accomplish this seamlessly. You must look at the formatting of an IP packet before IP address remapping can be explained.

Every IP packet that is transmitted across the Netopia R2121’s LAN interface or across the WAN interface to the Internet contains several bits of information that indicate to any device where the packet is going and where it came from. In particular you have the source and destination port and source and destination IP addresses.

A port is used within IP to define a particular type of service and could be either a Transmission Control Protocol (TCP) port or User Datagram Protocol (UDP) port. Both TCP and UDP are protocols that use IP as the underlying transport mechanism. The major difference between TCP and UDP is that TCP is a reliable delivery service whereas UDP is a “best effort” delivery service. A list of well known TCP or UDP ports and services can be found in RFC 1700.

If Workstation A wants to communicate with a World Wide Web (WWW) Server on the Internet and the Netopia R2121 does not have NAT enabled, Workstation A forms an IP packet with the source IP address of 192.168.5.2 and destination IP address of 163.176.4.32. The source port could be 400 while the destination port would be 80 (WWW server). The Netopia R2121 then looks at this IP packet, determines the best routing method and sends that packet on its way across the WAN interface to the WWW Server on the Internet.

With NAT enabled the Netopia R2121 does something different. For example, suppose that Workstation A again wants to communicate with the WWW Server on the Internet. Workstation A forms an IP packet with the source IP address of 192.168.5.2 and destination IP address of 163.176.4.32 and source port could be 400 while the destination port would be 80 (WWW server).

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Netopia R2121 manual User’s Reference Guide
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R2121 specifications

The Netopia R2121 is a powerful and versatile router designed for both home and office environments, providing seamless connectivity and robust performance for various networking needs. This device offers a range of features and technologies that cater to the demands of modern users seeking reliable internet access, speed, and security.

One of the standout characteristics of the Netopia R2121 is its dual-band technology, which operates on both the 2.4 GHz and 5 GHz frequency bands. This capability allows users to enjoy faster speeds and less interference, as the 5 GHz band is typically less congested than the traditional 2.4 GHz band. With the ability to support multiple devices simultaneously, the R2121 ensures that users can stream videos, play online games, and conduct video conferences without experiencing lag or connectivity issues.

The router is equipped with advanced security features, including WPA3 encryption, which provides enhanced protection against unauthorized access and data breaches. The R2121 also supports a robust firewall system that guards against external threats, ensuring that the user's network remains secure. Additionally, the router includes parental controls, allowing users to manage and restrict internet access for specific devices or set time limits for usage, making it an excellent choice for families.

Another significant advantage of the Netopia R2121 is its extensive coverage area. With high-gain antennas and advanced beamforming technology, the router can deliver strong and stable Wi-Fi signals even in larger homes or office spaces. This technology focuses the Wi-Fi signal directly toward connected devices, minimizing dead zones and improving overall connectivity.

The R2121 also supports both IPv4 and IPv6, ensuring compatibility with current and future internet technologies. This forward-thinking design makes it a future-proof solution for users looking to invest in a reliable router.

In terms of setup and management, the Netopia R2121 features a user-friendly web interface that allows users to easily customize settings, monitor network performance, and manage connected devices. The inclusion of mobile app support further enhances the user experience, enabling remote monitoring and control of the network from anywhere.

Overall, the Netopia R2121 stands out as a robust and reliable router that combines advanced features, enhanced security, and excellent performance, making it an ideal choice for home and business users alike. With its focus on delivering seamless connectivity and comprehensive management options, the R2121 is well-suited for today's connected lifestyles.
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