Linux+ Guide to Linux Certification, Second Edition Chapter 15 Configuring Network Services and Security

Linux+ Guide to Linux Certification, 2e2 Objectives Identify and configure common network services Configure routing and firewalls Describe the different facets of Linux security Increase the security of a Linux computer Outline measures that can be used to detect a Linux security breach

Linux+ Guide to Linux Certification, 2e3 Network Services Processes that provide some type of valuable service for client computers on network Must identify types and features of network services before they can be configured Important to configure network-related services, such as routing and firewalls

Linux+ Guide to Linux Certification, 2e4 Identifying Network Services Port: Number uniquely identifying a network service –Ensure that packets delivered to proper service –Range from 0 to /etc/services file: Lists ports and associated protocol Well-known port: Ports from 0 to 1024 –Used by common networking services

Linux+ Guide to Linux Certification, 2e5 Identifying Network Services (continued) Table 15-1: Common well-known ports

Linux+ Guide to Linux Certification, 2e6 Identifying Network Services (continued) Internet Super Daemon (xinetd): Initializes and configures many networking services Standalone daemons: Daemons normally started at boot-up –e.g., Apache Web server –Configure themselves without assistance –ntsysv utility can configure most standalone daemons to start in various runlevels

Linux+ Guide to Linux Certification, 2e7 Identifying Network Services (continued) Figure 15-1: Interacting with network services

Linux+ Guide to Linux Certification, 2e8 Configuring Common Network Services Table 15-2: Common network services

Linux+ Guide to Linux Certification, 2e9 Configuring Common Network Services (continued) Table 15-2 (continued): Common network services

Linux+ Guide to Linux Certification, 2e10 Configuring Common Network Services (continued) Table 15-2 (continued): Common network services

Linux+ Guide to Linux Certification, 2e11 Configuring Common Network Services (continued) Table 15-2 (continued): Common network services

Linux+ Guide to Linux Certification, 2e12 Configuring Common Network Services (continued) Table 15-2 (continued): Common network services

Linux+ Guide to Linux Certification, 2e13 Configuring DNS Zone: Portion of DNS administered by one or more DNS servers Forward lookup: FQDN resolved to IP address Reverse lookup: IP address resolved to FQDN

Linux+ Guide to Linux Certification, 2e14 Configuring DNS (continued) Figure 15-2: The DNS lookup process

Linux+ Guide to Linux Certification, 2e15 Configuring DNS (continued) Iterative query: Resolved without use of top-level DNS servers Recursive query: Resolved with the use of top-level DNS servers DNS cache file: Contains IP addresses of top-level DNS servers

Linux+ Guide to Linux Certification, 2e16 Configuring DNS (continued) Master or primary DNS server: Contains read/write copy of zone Slave or secondary DNS server: Contains read- only copy of zone Zone transfer: Copying zone resource records from master to slave DNS server

Linux+ Guide to Linux Certification, 2e17 Configuring DNS (continued) Table 15-3: Common zone configuration files

Linux+ Guide to Linux Certification, 2e18 Configuring DNS (continued) Table 15-3 (continued): Common zone configuration files

Linux+ Guide to Linux Certification, 2e19 Configuring DHCP Send DHCP broadcast on network –Request IP configuration information DHCP server leases IP address to client computer for a period of time –Ensures each client has unique IP address /etc/dhcpd.conf file: Configure computer as a DHCP server –List appropriate IP address range for network

Linux+ Guide to Linux Certification, 2e20 Configuring Apache Most common Web server Document root directory: Stores default HTML content for a Web server –/var/www/html on Fedora Linux –Default document is index.html /etc/httpd/conf/httpd.conf: Default configuration file Directive: Line within a configuration file

Linux+ Guide to Linux Certification, 2e21 Configuring Apache (continued) Table 15-4: Common httpd.conf directives

Linux+ Guide to Linux Certification, 2e22 Configuring Samba SaMBa daemon: Emulates SMB protocol Windows computers advertise computer names using NetBIOS protocol –Can use NetBIOS name daemon to create and advertise NetBIOS name Connect Windows computers to Linux server smbpasswd command: Generate Samba passwords

Linux+ Guide to Linux Certification, 2e23 Configuring Samba (continued) /etc/samba/smb.conf: Default Samba configuration file /etc/rc.d/init.d/smb start: Start Samba and NetBIOS name daemons –Restart if smb.conf changed

Linux+ Guide to Linux Certification, 2e24 Configuring NFS Create directory containing information to share Edit /etc/exports file: –Add line listing directory to be shared and options Run exportfs –a –Update list of exported filesystems Restart the NFS processes

Linux+ Guide to Linux Certification, 2e25 Configuring FTP Very secure FTP daemon (vsftpd): Packaged with Fedora Linux To configure (assuming logon as “user1”): –Create directory below user1’s home directory to host the files Ensure user1 owns directory –Run /etc/rc.d/init.d/vsftpd start Start vsftpd daemon

Linux+ Guide to Linux Certification, 2e26 Configuring NIS Network Information Service (NIS): Coordinate common configuration files across several computers –Computers belong to a NIS domain, use NIS map to access configuration information –Most commonly used for password databases

Linux+ Guide to Linux Certification, 2e27 Configuring NIS (continued) Define the NIS domain via domainname command Add “ NISDOMAIN=‘NIS_domain’ ” to /etc/sysconfig/network file –Configure NIS domain at boot time Add “domain server ” to /etc/yp.conf file –Query specific NIS server

Linux+ Guide to Linux Certification, 2e28 Configuring the Secure Shell Daemon Secure Shell daemon (sshd): Allows use of ssh utility to log in to network servers /etc/ssh/sshd_config file: Contains configuration options Uses challenge-response authentication by default

Linux+ Guide to Linux Certification, 2e29 Configuring the Secure Shell Daemon (continued) Supported encryption standards: –Triple Data Encryption Standard (3DES) –Advanced Encryption Standard (AES) –Blowfish –Carlisle Adams Stafford Tavares (CAST) –ARCfour

Linux+ Guide to Linux Certification, 2e30 Routing and Firewall Services Network services not provided entirely by network daemons –Provided by Linux kernel –Do not listen to a particular port

Linux+ Guide to Linux Certification, 2e31 Routing Route table: Indicates which networks are connected to network interfaces Route command: Manipulate the route table Multihomed hosts: Computers with multiple network interfaces IP forwarding: Forwarding TCP/IP packets between networks Routing: Forwarding data packets between networks

Linux+ Guide to Linux Certification, 2e32 Routing (continued) Enabling routing: –Place number 1 in /proc/sys/net/ipv4/ip_forward file –Place “net.ipv4.ip_forward = 1” in /etc/sysctl.conf file

Linux+ Guide to Linux Certification, 2e33 Routing (continued) Large networks may have several routers route add command: Add entries to route table route del command: Remove entries from route table Can use ip command to add entries to route table

Linux+ Guide to Linux Certification, 2e34 Routing (continued) Figure 15-3: A sample routed network

Linux+ Guide to Linux Certification, 2e35 Routing (continued) Contents of route table lost when computer powered off –Add to /etc/rc.d/rc.local file Most routers configured with a default gateway –For packets addressed to destinations not in route table traceroute command: Troubleshoot routing –Displays routers between current and remote computer

Linux+ Guide to Linux Certification, 2e36 Firewall Services netfilter/iptables: Used to create a firewall –Discard network packets according to chains of rules Chains: Specify general type of network traffic to apply rules to Rules: Match network traffic to be allowed or dropped

Linux+ Guide to Linux Certification, 2e37 Firewall Services (continued) Three chain types: –INPUT chain: Incoming packets –FORWARD chain: Packets passing through computer –OUTPUT chain: Outgoing packets iptables command: Creates rules for a chain

Linux+ Guide to Linux Certification, 2e38 Firewall Services (continued) Table 15-5: Common iptables commands

Linux+ Guide to Linux Certification, 2e39 Security Linux systems typically available across networks such as the Internet Should improve local and network security Understand how to detect intruders who breach the system

Linux+ Guide to Linux Certification, 2e40 Securing the Local Computer Limit access to computer itself –Prevent malicious users from accessing files Server closet: Secured room to store servers Remove floppy and CD-ROM devices from workstations Ensure BIOS prevents booting from USB ports

Linux+ Guide to Linux Certification, 2e41 Securing the Local Computer (continued) Ensure BIOS password is set Set boot loader password in LILO or GRUB configuration file Limit access to graphical desktops and shells Minimize root user’s time logged in

Linux+ Guide to Linux Certification, 2e42 Securing the Local Computer (continued) nohup command: Prevents other commands from exiting when parent process killed su (switch user) command: Switch current user account to another sudo command: Perform commands as another user via entries in /etc/sudoers file

Linux+ Guide to Linux Certification, 2e43 Protecting Against Network Attacks Always a possibility that crackers can manipulate a network service Buffer overrun: Network service altered in memory Minimize number of running network services nmap (network mapper) command: Scan ports on network computers –See what network services are running

Linux+ Guide to Linux Certification, 2e44 Protecting Against Network Attacks (continued) Enable encryption on essential network services Ensure network service daemons not run as root user when possible New network service versions usually include fixes for known network attacks –Keep network services up-to-date

Linux+ Guide to Linux Certification, 2e45 Protecting Against Network Attacks (continued) TCP wrapper: Run network daemon with additional security via /etc/hosts.allow and /etc/hosts.deny files Examine permissions for files and directories associated with system and network services

Linux+ Guide to Linux Certification, 2e46 Detecting Intrusion Log files can contain information or irregularities indicating an intrusion Review system log files associated with authentication Pluggable Authentication Module (PAM): Handles authentication requests by daemons –Log file in /var/log/secure

Linux+ Guide to Linux Certification, 2e47 Detecting Intrusion (continued) Check /var/log/wtmp log file –Lists users who receive BASH shells Tripwire: Monitors files and directories Intrusion Detection System (IDS): Detect unauthorized access

Linux+ Guide to Linux Certification, 2e48 Detecting Intrusion (continued) Table 15-6: Common Linux intrusion detection systems