Planning a Leased-Line Link

Setting up a leased-line link involves configuring the peer at one end of a switched or unswitched service leased from a provider.

This section includes the following information:

• Planning information for a leased-line link

• Explanation of the sample link that is shown in Figure 30–2

For an introduction to leased-line links, refer to Leased-Line PPP Overview. For tasks on setting up the leased line, see Chapter 32, Setting Up a Leased-Line PPP Link (Tasks).

Before You Set Up the Leased-Line Link

When your company rents a leased-line link from a network provider, you typically configure only the system at your end of the link. The peer at the other end of the link is maintained by another administrator. This individual might be a system administrator at a remote location in your company or a system administrator at an ISP.

Hardware That Is Needed for a Leased-Line Link

In addition to the link media itself, your end of the link requires the following hardware:

• Synchronous interface for your system

• Synchronous unit (CSU/DSU)

• Your system

Some network providers include a router, synchronous interface, and a CSU/DSU as part of the customer premises equipment (CPE). However, necessary equipment varies, based on the provider and any governmental restrictions in your locale. The network provider can give you information about the unit that is needed, if it is not provided with the leased line.

Information to Be Gathered for the Leased-Line Link

Before you configure the peer at your end of a leased line, you might need to gather the items or information that is listed in the next table.

Table 30–4 Planning for a Leased-Line Link

Information	Action
Device name of the interface	Refer to the Interface card documentation.
Configuration instructions for the synchronous interface card	Refer to the Interface card documentation. You need this information to configure the HSI/S interface. You might not need to configure other types of interface cards.
(Optional) IP address of the remote peer	Refer to the service provider documentation or contact the system administrator of the remote peer. This information is needed only if the IP address is not negotiated between the two peers.
(Optional) Name of the remote peer	Refer to the service provider documentation or contact the system administrator of the remote peer.
(Optional) Speed of the link	Refer to the service provider documentation or contact the system administrator of the remote peer.
(Optional) Compression that is used by the remote peer	Refer to the service provider documentation or contact the system administrator of the remote peer.

Example—Configuration for a Leased-Line Link

The tasks in Chapter 32, Setting Up a Leased-Line PPP Link (Tasks) show how to implement the goal of a medium-sized organization called LocalCorp to provide Internet access for its employees. Currently, the employees' computers are connected on a private corporate intranet.

LocalCorp requires speedy transactions and access to the many resources on the Internet. The organization signs a contract with Far ISP, a service provider, that allows LocalCorp to set up its own leased line to Far ISP. Then, LocalCorp leases a T1 line from Phone East, a telephone company. Phone East puts in the leased line between LocalCorp and Far ISP and provides to Local Corp a CSU/DSU that is already configured.

The tasks set up a leased-line link with the following characteristics:

• LocalCorp has set up a system as a gateway router, which forwards packets over the leased line to hosts on the Internet.

• Far ISP also has set up a peer as a router to which leased lines from customers are attached.

Figure 30–2 Sample Leased-Line Configuration

In the figure, the machine that is set up for PPP at LocalCorp is a router with a connection to the corporate intranet through its hme0 interface. The second connection is through the machine's HSI/S interface (hih1) to the CSU/DSU digital unit. The CSU/DSU then connects to the installed leased line. The link between LocalCorp and Far ISP is initiated after the administrator at LocalCorp configures the HSI/S interface and PPP files, and then types the /etc/init.d/pppd start command.

Where to Get More Information About Leased Lines

Task	For Information
Set up a client on a leased line	Chapter 32, Setting Up a Leased-Line PPP Link (Tasks)
Get an overview of leased lines	Leased-Line PPP Overview