Chapter 10 Networking and the Internet ITSC 1458

Hostnames Linux provides several ways to associate hostnames with IP addresses. One of these is to store a list of names and addresses in the /etc/hosts file. cat /etc/hosts localhost bravo.example.combravo Localhost - allows networking software to operate on th local machine without going onto a physical network FQDN - fully qualified domain name Nickname – locally unique

NIS The second way to associate hostnames with Ips is to use NIS (Network Information Service). NIS stores info in a database and is useful only for host information within a single administrative domain. Hosts outside of the domain can’t access the database.

DNS The third way to associate hostnames with IP addresses is to use DNS. DNS arranges the entire network namespace as a hierarchy. Each domain in the DNS manages its own namespace (addressing and name resolution), and each domain can query for any host or IP address by following the tree up or down the namespace until it finds the appropriate domain.

Communication Commands Hostname – shows or sets the system’s host name (default is localhost.localdomain) – hostname Displays the hostname – hostname Anaconda Changes the hostname to Anaconda – allows you to refer to a user (msmith) on a remote server (remotehost). uname – lists host information – uname –n lists hostname – uname –alists kernel name (-s), hostname (-n), kernel- release (-f), kernel version (-v), machine hardware name (-m), processor type (-p), hardware platform (-i), and operating system (-o)

Comm. Commands domainname – show or set the system’s domain name – domainnamelists the domain name – domainname newnamesets the domain name dnsdomainname – show or set the system’s DNS domain name

finger Finger – displays information about local and remote users. – displays information about all users on the remote system bravo – finger displays information about the single user alex on remote system bravo. – F – inger jane displays info on all local users with “jane” in /etc/passwd. Displays username, shell, home directory, and last login. Finger queries in.fingerd that runs on the system being queried. To disable finger, – set disable = yes in /etc/xinetd.d/finger – service finger restart

Network Utilities Trusted Hosts – some commands such as rcp and rsh work only if the remote system trusts your local computer. Trusted systems are listed in the /etc/hosts.equiv file. OBSOLETE. You should not allow rcp, rsh, or any rcommands on your network. OpenSSH has tools that replace the r (remote) commands with more secure alternatives.

telnet vs. ssh telnet – remotely access another system. Sends info in clear text. Don’t allow. Can be used as a debugging tool to connect to other ports rather than the standard 23. – telnet smtpsrv 25 -connects to port 25 using SMTP commands ssh – more secure alternative. Assumes that your username and password are the same on the remote system as they are on the querying system.

ftp ftp – transfers files over a network in clear text. Login is also in clear text. Used for publicly available downloads.Must connect to a server and must log in to the server. – ftp

ping ICMP Echo request/echo response Checks for connectivity (and DNS if use domain name) – ping Ctrl c ends

traceroute Traces the route that an IP packet follows, including all hops, to its destination. – traceroute

Host and dig Host looks up an IP address given a name, or vice versa. – host – host Dig (domain information groper) queries DNS servers and individual machines for information about a domain.

jwhois jwhois – replaces whois and queries a whois server for information about an Internet side. Returns site contact and registry information. Faster than whois – jwhois victoriacollege.edu

DNS DNS is a distributed service to provide IP address to domain name resolution. Nameservers on thousands of machines worldwide cooperate to keep the database up-to-date. No one system has a complete copy of the database. 6 original top-level domains: com, edu, gov, mil, net, org FQDN – fully-qualified domain name – a system’s complete name. Top-level domain appears last – anaconda.marty.com DNS service – bind (most common) – client/server system.

nis Network Information Service – simplifies the maintenance of frequently used administrative files by keeping them in a central database and having clients contact the database server to retrieve information from the database.

nfs Network Filesystem – allows a server to share selected local directory hierarchies with client systems. Files on the remote fileserver appear as if they are present on the local system.