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System Administration Guide: Security Services
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Controlling Network Access

Computers are often part of a configuration of computers. This configuration is called a network. A network allows connected computers to exchange information. Networked computers can access data and other resources from other computers on the network. Computer networks create a powerful and sophisticated computing environment. However, networks also complicate computer security.

For example, within a network of computers, individual machines allow the sharing of information. Unauthorized access is a security risk. Because many people have access to a network, unauthorized access is more likely, especially through user error. A poor use of passwords can also allow unauthorized access.

Network Security Mechanisms

Network security is usually based on limiting or blocking operations from remote systems. The following figure describes the security restrictions that you can impose on remote operations.

Figure 2-1 Security Restrictions for Remote Operations
Diagram shows three ways to restrict access to remote systems: a firewall system, an authentication mechanism, and an authorization mechanism.

Authentication and Authorization for Remote Access

Authentication is a way to restrict access to specific users when these users access a remote system. Authentication can be set up at both the system level and the network level. After a user has gained access to a remote system, authorization is a way to restrict operations that the user can perform. The following table lists the services that provide authentication and authorization.

Table 2-3 Authentication and Authorization Services for Remote Access



For More Information


IPsec provides host-based and certificate-based authentication and network traffic encryption.

Chapter 19, IP Security Architecture (Overview), in System Administration Guide: IP Services


Kerberos uses encryption to authenticate and authorize a user who is logging in to the system.

For an example, see How the Kerberos Service Works.


The LDAP directory service and the NIS+ name service can provide both authentication and authorization at the network level.

System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP) and System Administration Guide: Naming and Directory Services (NIS+)

Remote login commands

The remote login commands enable users to log in to a remote system over the network and use its resources. Some of the remote login commands are rlogin, rcp, and ftp. If you are a “trusted host,” authentication is automatic. Otherwise, you are asked to authenticate yourself.

Chapter 29, Accessing Remote Systems (Tasks), in System Administration Guide: Network Services


The Simple Authentication and Security Layer (SASL) is a framework that provides authentication and optional security services to network protocols. Plugins enable you to choose an appropriate authentication protocol.

SASL (Overview)

Secure RPC

Secure RPC improves the security of network environments by authenticating users who make requests on remote machines. You can use either the UNIX, DES, or Kerberos authentication system for Secure RPC.

Overview of Secure RPC

Secure RPC can also be used to provide additional security in an NFS environment. An NFS environment with secure RPC is called Secure NFS. Secure NFS uses Diffie-Hellman authentication for public keys.

NFS Services and Secure RPC

Solaris Secure Shell

Solaris Secure Shell encrypts network traffic over an unsecured network. Solaris Secure Shell provides authentication by the use of passwords, public keys, or both. Solaris Secure Shell uses RSA and DSA authentication for public keys.

Solaris Secure Shell (Overview)

A possible substitute for Secure RPC is the Solaris privileged port mechanism. A privileged port is assigned a port number less than 1024. After a client system has authenticated the client's credential, the client builds a connection to the server by using the privileged port. The server then verifies the client credential by examining the connection's port number.

Clients that are not running Solaris software might be unable to communicate by using the privileged port. If the clients cannot communicate over the port, you see an error message that is similar to the following:

“Weak Authentication
NFS request from unprivileged port”

Firewall Systems

You can set up a firewall system to protect the resources in your network from outside access. A firewall system is a secure host that acts as a barrier between your internal network and outside networks. The internal network treats every other network as untrusted. You should consider this setup as mandatory between your internal network and any external networks, such as the Internet, with which you communicate.

A firewall acts as a gateway and as a barrier. A firewall acts as a gateway that passes data between the networks. A firewall acts as a barrier that blocks the free passage of data to and from the network. The firewall requires a user on the internal network to log in to the firewall system to access hosts on remote networks. Similarly, a user on an outside network must first log in to the firewall system before being granted access to a host on the internal network.

A firewall can also be useful between some internal networks. For example, you can set up a firewall or a secure gateway computer to restrict the transfer of packets. The gateway can forbid packet exchange between two networks, unless the gateway computer is the source address or the destination address of the packet. A firewall should also be set up to forward packets for particular protocols only. For example, you can allow packets for transferring mail, but not allow packets for the telnet or the rlogin command.

In addition, all electronic mail that is sent from the internal network is first sent to the firewall system. The firewall then transfers the mail to a host on an external network. The firewall system also receives all incoming electronic mail, and distributes the mail to the hosts on the internal network.

Caution - A firewall prevents unauthorized users from accessing the hosts on your network. You should maintain strict and rigidly enforced security on the firewall, but security on other hosts on the network can be more relaxed. However, an intruder who can break into your firewall system can then gain access to all the other hosts on the internal network.

A firewall system should not have any trusted hosts. A trusted host is a host from which a user can log in without being required to supply a password. A firewall system should not share any of its file systems, or mount any file systems from other servers.

The following technologies can be used to harden a system into a firewall:

Encryption and Firewall Systems

Most local area networks transmit data between computers in blocks that are called packets. Through a procedure that is called packet smashing, unauthorized users from outside the network can corrupt or destroy data.

Packet smashing involves capturing the packets before the packets reach their destination. The intruder then injects arbitrary data into the contents, and sends the packets back on their original course. On a local area network, packet smashing is impossible because packets reach all systems, including the server, at the same time. Packet smashing is possible on a gateway, however, so make sure that all gateways on the network are protected.

The most dangerous attacks affect the integrity of the data. Such attacks involve changing the contents of the packets or impersonating a user. Attacks that involve eavesdropping do not compromise data integrity. An eavesdropper records conversations for later replay. An eavesdropper does not impersonate a user. Although eavesdropping attacks do not attack data integrity, the attacks do affect privacy. You can protect the privacy of sensitive information by encrypting data that goes over the network.

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