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Lesson 4 Optimizing remote subnets
Objective Determine the number of subnets and IP addresses used by remote network segments.

Optimizing Remote Subnets

Determine number of IP addresses

Remote networks require special consideration when you develop an IP addressing scheme to ensure that traffic is properly routed and that Internet access is maintained.

Private point-to-point Connections

F or private point-to-point connections, such as dedicated 56 kbps leased lines or T1 connections, a separate subnet is required for each point-to-point connection. Each point-to-point connection requires two IP addresses to support dynamic routing protocols as illustrated below.
Private point-to-point connections
Private point-to-point connections

Multi-point Connections

For multi-point connections, such as an X.25 or other packet-switched private networks, one subnet is sufficient for all connections. An IP address for each connection or virtual circuit is required in the multi-point connection.
A packet assembler-disassembler (PAD) [1] is used on X.25 networks to connect computers to the X.25 network Cloud as shown below. The X.25 Cloud is a world-wide private network that consists of a bunch of network devices that separate PADs.
Multi-point connections
Multi-point connections

Because no public addressing scheme can see point-to-point and multi-point connections, you can use private addressing to create each subnet. If the addresses used for point-to-point or multi-point subnets are allocated from the range of addresses used by other devices on the private network, VLSM or CIDR is recommended to conserve IP addresses.

VPN connections over the Internet

To connect to a VPN client, each VPN server requires a public address. This address becomes one end of the communications tunnel. The VPN client receives an address from the VPN server either via DHCP or from a static address pool configured on the VPN server. When communicating over the VPN connection, the VPN client uses the address assigned by the DHCP Server for the VPN interface to access intranetwork resources. Any IP addressing design must account for the public address and the range of private network addresses required by the VPN server design. A private network address is required for each VPN client that simultaneously accesses the intranetwork.
The next lesson examines QoS.
[1]Packet assembler-disassembler (PAD): A network device used on X.25 internetworks.