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System Administration Guide: Network Services
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A version of PPP that was included with the Solaris Operating System from the Solaris 2.4 to the Solaris 8 releases. asppp supported asynchronous PPP communications only.

asynchronous PPP

A form of PPP that runs over asynchronous serial lines, which transfer data one character at a time. The most common form of PPP configuration, the dial-up link, uses asynchronous PPP communications.


The act of verifying the identity that is supplied over the network by a remote user or entity, such as a program. Some authentication protocols enable you to build databases of authentication credentials from potential users. Other authentication protocols use certificate chains of trust that are generated by a certificate authority for authentication purposes. These credentials can authenticate users when they try to communicate with you or use your site's services.


A data-link layer procedure that is used to transmit packets to every machine on a subnet. Broadcast packets are typically not routed beyond the subnet.

Callback Control Protocol (CBCP)

A proprietary Microsoft PPP extension that is used to negotiate a callback session. Solaris PPP 4.0 supports only the client (initial caller) side of this protocol.

channel service unit (CSU)

A synchronous telecommunications device that provides a local interface to a leased telecommunications line and terminates that line. In the United States, a CSU terminates a T1 line and provides a DS1 or DSX interface. Internationally, the CSU is typically owned by the telephone company provider.

See also CSU/DSU and data service unit (DSU).


The Challenge-Handshake Authentication Protocol is an authentication protocol that can be used to verify the identity of a caller on a PPP link. CHAP authentication uses the notion of the challenge and response, where the machine that receives a call challenges the caller to prove its identity.

See also password authentication protocol (PAP).

CHAP secret

An ASCII or binary string that is used for identification purposes and is known to both peers on a PPP link. The CHAP secret is stored in clear text in a system's /etc/ppp/chap-secrets file but is never sent over the PPP link, not even in encrypted form. The CHAP protocol verifies that a hash of the CHAP secret that is used by a caller matches a hash of the CHAP secret entry for the caller in the recipient's /etc/ppp/chap-secrets file.

chat script

Instructions that tell a modem how to establish a communications link between itself and a remote peer. Both the PPP and UUCP protocols use chat scripts for establishing dial-up links and dial-back calling.

Compression Control Protocol (CCP)

A subprotocol of PPP that negotiates the use of data compression on the link. Unlike header compression, CCP compresses all data within packets that are sent on the link.


A synchronous telecommunications device that combines the CSU and DSU devices and is used on a leased-line PPP link. The CSU/DSU translates signals from a peer to a leased line. Most CSU/DSUs do not need a chat script to establish the link. CSU/DSUs are often configured by the leased-line provider.

See also channel service unit (CSU) and data service unit (DSU).

data service unit (DSU)

A synchronous telecommunications device that is used on a leased-line PPP link. The DSU converts between data-framing formats that are used on telecommunications lines and provides a standard data communications interface.

See also channel service unit (CSU) and CSU/DSU.

dial-in server

The peer that negotiates and establishes the recipient end of a dial-up PPP link after receiving a call from a dial-out machine. Though the term “dial-in server” is in common use, the dial-in server does not function in accordance with the client-server paradigm. Rather, it is simply the peer that responds to the request to set up a dial-up link. After it is configured, a dial-in server can receive calls from any number of dial-out machines.

dial-out machine

The peer that initiates the call to establish a dial-up PPP link. After it is configured, the dial-out machine can call any number of dial-in servers. The dial-out machine typically provides authentication credentials before the dial-up link can be established.

dial-up PPP link

A PPP connection that involves a peer and a modem at either end of a telephone line or similar communications medium, such as a medium that is provided by ISDN. The term “dial-up” refers to the sequence in link negotiation when the local modem dials up the remote peer by using the peer's telephone number. The dial-up link is the most common and least expensive PPP configuration.

Directory Agent (DA)

Optional SLP agent that stores and maintains a cache of service advertisements that are sent by the service agent (SA). When deployed, the DA resolves user agent (UA) service requests. The DA responds to active solicitations from the SA and UA for directory advertisements. As a result, the SA and UA discover the associated DAs and scopes. A DA sends periodic unsolicited advertisements through which UAs and SAs discover the DA within shared scopes.


A scripting format that is used in PPP and UUCP chat scripts. The chat script begins with the text or instruction to expect from the remote peer. The next line contains the response to be sent from the local host after it receives the correct expect string from the peer. Subsequent lines repeat the expect-send instructions between local host and peer until all instructions that are required to establish communications are successfully negotiated.

extended accounting

A flexible way to record resource consumption on a task or process basis in the Solaris Operating System.

Internet Protocol Control Protocol (IPCP)

A subprotocol of PPP that negotiates the IP addresses of the peers on the link. IPCP also negotiates header compression for the link and enables the use of the network layer protocols.

Internet Protocol Version 6 Control Protocol (IPV6CP)

See Internet Protocol Control Protocol (IPCP).

ISDN terminal adaptor (TA)

A signal-adapting device that provides a modem-like interface for a dial-up PPP link over an ISDN network. You use the same Solaris PPP 4.0 configuration files to configure an ISDN TA as you use for configuring a standard modem.

leased-line PPP link

A PPP connection that involves a host and a CSU/DSU that are connected to a synchronous network medium leased from a provider. OC3 and T1 are common examples of leased-line media. Though easier to administer, leased-line links are more expensive than dial-up PPP links and, therefore, are less common.

legacy services

A networked service that is not SLP-enabled. You can create a proxy registration to register a legacy service with SLP. SLP-based clients can then discover legacy services (see Chapter 10, Incorporating Legacy Services).


In PPP, the communications connection that is negotiated and established between two peers. Solaris PPP 4.0 supports two types of links: dial up and leased line.

link control protocol (LCP)

A subprotocol of PPP that is used to negotiate the initial set of link parameters between the peers. Part of the function of LCP is to test the link integrity, so many link-related problems manifest themselves as LCP failure.

Microsoft CHAP (MS-CHAP)

A proprietary Microsoft authentication protocol for PPP. Solaris PPP 4.0 supports versions 1 and 2 of this protocol in both client and server mode.


A network layer procedure that is used to send datagram packets to multiple machines on an IP network. Packets are not handled by every machine as is the situation with broadcast routing. Multicast requires that routers be configured with special routing protocols.

password authentication protocol (PAP)

An authentication protocol that can be used to verify the identity of a caller on a PPP link. PAP uses a cleartext password that is passed over the link, which makes it possible to store the password on one of the endpoint machines. For example, PAP can use the login and password entries in the UNIX passwd database on the machine that receives a call to verify the identity of the caller.

See also CHAP.


In PPP, an individual computer at one end of a PPP communications link, which consists of two peers that are connected by communications media. You can configure many types of computing equipment as a peer, such as a workstation, personal computer, router, or mainframe.

point-to-point protocol (PPP)

A data-link layer protocol that provides a standard method for transferring datagrams over point-to-point media. A PPP configuration consists of two endpoint computers called peers, and the telephone lines or another bidirectional link that the peers use for communication. The hardware and software connection between the two peers is considered the PPP link.

PPP is composed of a number of subprotocols, including PAP, CHAP, LCP, and CCP. Numerous PPP implementations are available. The Solaris 9 Operating System includes Solaris PPP 4.0.

PPP over Ethernet (PPPoE)

A proprietary protocol from RedBack Networks that enables hosts to run PPP sessions over an Ethernet link. PPPoE is commonly used with Digital Subscriber Line (DSL) services.


A grouping of UAs and SAs that are arranged administratively, topologically, or in some other manner. You can use scopes to modify how you provision access to services across the enterprise.

service advertisements

Information that is distributed by an SA that describes a service. A service advertisement consists of a URL and a collection of attribute/value list pairs that describe a service. All service advertisements have a lifetime. After the lifetime expires, a service advertisement is no longer valid unless reregistered.

Service Agent (SA)

The SLP agent that maintains service advertisements for networked services. If no DA is available, the SA answers multicast service requests from UAs. If a DA is available, the SA registers and, optionally, deregisters services with DAs that support its scopes.

service URL

A URL that is used to advertise the network location of services. The URL contains the service type, host name, or network address of the service host. The URL might also contain a port number and other information that is required to use the service.

SLP daemon (slpd)

The daemon process that acts as a DA or an SA server in the Solaris implementation of SLP. Service processes on the host register service advertisements with slpd instead of maintaining the advertisements individually. Each process contains an SA client library that communicates with slpd when the daemon is configured as the SA server. The SLP daemon forwards all registrations and deregistrations to DAs. The daemon times out expired service advertisements and maintains a table of the available DAs by performing active and passive DA discovery. Through such mechanisms, DA information is provided to UA clients. UA clients use slpd on a host only for DA information. You can optionally configure slpd as a DA.

synchronous PPP

A form of PPP that runs over synchronous digital lines, which transfer data as a continuous stream of raw bits. The leased-line PPP link uses synchronous PPP.

trusted callers

In PPP, remote peers that a dial-in server grants access to by including the peers' security credentials in the server's PAP or CHAP secrets database.

User Agent (UA)

The SLP agent that acts on behalf of the user application. The agent queries for the identity of corresponding scopes, directory agents, and service advertisements.

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