what is an firewall system _learningmore

 

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.

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 21, 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.