System Administration Guide: Security Services

Controlling Network Access

Computers are often part of a configuration of computers. The 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. Networking has created a powerful and sophisticated way of computing. However, networking also jeopardizes computer security.

For instance, within a network of computers, individual machines are open to allow the sharing of information. Also, because many people have access to the network, unwanted access is more likely, especially through user error. For example, a poor use of passwords can allow unwanted 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 machine. Authentication can be set up at both the machine level and the network level. Once a user gains access to a remote machine, authorization is a way to restrict operations that the user can perform on the remote system. The following table lists the types of authentications and authorizations that can help protect your machines on the network against unauthorized use.

Table 2–5 Types of Authentication and Authorization for Remote Access



Where to Find Information 

LDAP and NIS+ 

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 (FNS and NIS+)

Remote login commands 

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

“Accessing Remote Systems (Tasks)” in System Administration Guide: Resource Management and Network Services

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 to the NFS environment. An NFS environment with secure RPC is called Secure NFS. 

NFS Services and Secure RPC

DES encryption 

The Data Encryption Standard (DES) encryption functions use a 56-bit key to encrypt a secret key. 

DES Encryption

Diffie-Hellman authentication 

This authentication method is based on the ability of the sending machine to use a common key to encrypt the current time. The receiving machine decrypts the common key. The machine then checks the time against its current time. 

Diffie-Hellman Authentication


Kerberos uses DES encryption to authenticate a user when logging in to the system.  

See How to Configure a Master KDC for an example.

Using Privileged Ports Between Solaris Systems

If you do not want to run Secure RPC, a possible substitute is the Solaris “privileged port” mechanism. A privileged port is assigned with a port number of 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.

Non-Solaris clients, however, 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. Each network approaches the other as untrusted. You should consider this setup as mandatory between your internal network and any external networks, such as the Internet, with which you want to 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 when the firewall 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 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 secure gateway computer to restrict the transfer of packets. The gateway can forbid packet exchange between two networks unless the gateway computer is the origin 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. ASET, when run at high security, disables the forwarding of Internet Protocol (IP) packets.

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 receives all incoming electronic mail, and distributes the mail to the hosts on the internal network.

Caution – 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 type in a password. A firewall system should not share any of its file systems, or mount any file systems from other servers.

ASET can be used to harden a machine into a firewall. ASET enforces high security on a firewall system, as described in Chapter 8, Using the Automated Security Enhancement Tool (Tasks). Similarly, IPsec provides firewall protection. For more information on using IPsec to protect network traffic, see “IPsec (Overview)” in System Administration Guide: IP Services.

Packet Smashing

Most local area networks transmit data between computers in blocks that are called packets. Through a procedure that is called packet smashing, unauthorized users can corrupt data. Data can also be destroyed. 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 machines, 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 are those attacks that 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. While 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. For how to encrypt IP datagrams, see “Internet Key Exchange” in System Administration Guide: IP Services.