Part III Network security #

Network transparency is one of the central characteristics of a Unix system. X, the windowing system of Unix operating systems, can use this feature in an impressive way. With X, it is no problem to log in to a remote host and start a graphical program that is then sent over the network to be displa…

OpenSSH is the SSH (secure shell) implementation that ships with SUSE Linux Enterprise Server, for securing network operations such as remote administration, file transfers, and tunneling insecure protocols. SSH encrypts all traffic between two hosts, including authentication, to protect against eavesdropping and connection hijacking. This chapter covers basic operations, plus host key rotation and certificate authentication, which are useful for managing larger SSH deployments.

Whenever Linux is used in a network environment, you can use the kernel functions that allow the manipulation of network packets to maintain a separation between internal and external network areas. The Linux netfilter framework provides the means to establish an effective firewall that keeps differ…

Today, Internet connections are cheap and available almost everywhere. However, not all connections are secure. Using a Virtual Private Network (VPN), you can create a secure network within an insecure network such as the Internet or Wi-Fi. It can be implemented in different ways and serves several purposes. In this chapter, we focus on the OpenVPN implementation to link branch offices via secure wide area networks (WANs).

Managing your own public key infrastructure (PKI) is traditionally done with the openssl utility. For admins who prefer a graphical tool, SUSE Linux Enterprise Server 15 SP4 includes XCA, the X Certificate and Key management tool (http://hohnstaedt.de/xca).

XCA creates and manages X.509 certificates, certificate requests, RSA, DSA, and EC private keys, Smartcards, and certificate revocation lists (CRLs). XCA supports everything you need to create and manage your own certificate authority (CA). XCA includes customizable templates that can be used for certificate or request generation. This chapter describes a basic setup.

Sysctl (system control) variables control certain kernel parameters that influence the behavior of different parts of the operating system, for example the Linux network stack. These parameters can be looked up in the proc file system, in /proc/sys. Many kernel parameters can be changed directly by …