------------------------- Week 11 Notes for NET2003 ------------------------- -Ian! D. Allen - idallen@idallen.ca Remember - knowing how to find out an answer is more important than memorizing the answer. Learn to fish! RTFM! (Read The Fine Manual) Keep up on your readings (Course Outline: average 5 hours/week homework) "ALN" = "Advanced Linux Networking" text Configuring DHCP (client) - ALN p.33, week10notes.txt ------------------------- - True/False: DHCP clients broadcast for a DHCP server. p.33 - True/False: Linux has only two common DHCP client packages. p.33 - What is the absolute pathname to the DHCP client start-up script? p.35 - Find the names of the DHCP client programs that are tried, in order, in your Mandrake Mini system DHCP client SysV start-up script. (Hint: the DHCP client program names all reside in the /sbin/ directory.) Of the DHCP client program file names tested, how many actually exist in your Mandrake Mini system? Which file is the smallest? - True/False: the "extra" config files listed for Mandrake in Table 2.1 are used to choose between static and DHCP network interfaces. p.36 - Give the absolute pathnames of the two typical files you must edit to configure a DHCP network interface under Mandrake. (week10notes) - True/False: to configure DHCP on a Mandrake system, you must use the "hostname", "ifconfig" and "route" commands. (week10notes) Configuring static networking - ALN p.36, week10notes.txt ----------------------------- - What four network parameters need to be set to manually configure a machine to be a "good network citizen" with a static IP address? (week10notes) - True/False: if you use any static network interfaces, you must always set all four network configuration parameters. (week10notes) - What command sets/shows the global host name of a Linux machine? (p.48, week10notes) - What command shows the IP addresses on each network interface? (p.36, week10notes) - What command shows the default gateway? (p.40-42, week10notes) - What command shows the list of DNS servers? (p.46-47, week10notes) - True/False: once you have put DNS servers in the /etc/resolv.conf file, you must start/stop the network using the /etc/init.d/network script to make the changes active. p.48 - True/False: to configure static addresses on a Mandrake system, you must use the "hostname", "ifconfig" and "route" commands. (week10notes) - True/False: a Linux computer with multiple network interfaces will normally have a main host name and also separate names for each network interface. p.49 - True/False: Using the "hostname", "ifconfig" and "route" commands makes permanent changes to your system that will re-appear on reboot. p.49 - True/False: a static configuration doesn't need a Gateway machine or default route. (week10notes) - Give the absolute pathnames of the three typical files you must edit to configure a static network interface under Mandrake. (week10notes) - True/False: to start the network under Mandrake, type "ifup eth0" or "ifup eth1". (week10notes) - True/False: giving a single interface name argument to the ifconfig command toggles the interface (if the interface is up, it takes it down; if down, it brings it up) p.37 - True/False: if you don't supply a netmask to the ifconfig command when you bring up an interface, the netmask is set based on the traditional TCP/IP class of the address. p.37 - What is the traditional/default netmask for IP address 10.34.56.78? p.39 Linux routing - ALN p.40 ------------- If your computer has simple network connectivity, you never need to use any of the low-level Linux network or routing commands. Either DHCP configures your system for you; or, you set up static routing using files /etc/sysconfig/network-scripts/ifcfg-eth?, /etc/sysconfig/network, and /etc/resolv.conf. The /etc/init.d/network script will use these files to add the correct routing entries to your machine. If you have special routing needs, you will need to understand Linux routing. - What are the two functions of the Linux routing table? p.40 - How does Linux find out the IP addresses of hosts on a directly-connected network? p.40 - What is the purpose of a "gateway" IP address? p.40 - True/False: Linux systems only need one gateway address. p.41 - What command configures the Linux routing table? p.40 - In which order does the kernel match an outgoing packet destination address against the table of routes? p.41 - What is another common name for the most general route in the routing table (the route that matches any address)? p.41 - How does using the ifconfig command affect the routing table? p.42 - True/False: using the route command without any parameters, or with just the "-n" parameter, clears the current routing table. p.42 - What is the most common use of the "route" command? p.44 - True/False: the ifconfig command also adds a route to your gateway. p.44 - What are the two steps needed to manually configure a machine with multiple interfaces and one gateway? p.44 - True/False: it is safe and normal for a router to run non-routing software (e.g. a GUI, web server, ssh, telnet, etc.). p.44 Configuring DHCP (server) - ALN Chapter 5 ------------------------- You can configure a computer to supply DHCP addresses to other computers on the same network (or networks). The addresses can be assigned at random from a common pool, or they can be made fixed (always the same address for the same computer). WARNING: DHCP is not software that you should enable if you are already on a network using DHCP! Having two DHCP servers on the same network will cause client machine failure when two clients are handed the same IP address by the two different DHCP servers. p.122 The most common DHCP server is named "dhcpd" from the ISC. p.116 - Describe the basics of how DHCP works. p.113 - True/False: DHCP cannot be configured to always assign the same address to the same computer network interface. p.113 - True/False: A Linux DHCP server cannot supply DHCP addresses to non-Linux DHCP clients. p.114 - Why is it not advisable to have public servers configure themselves using DHCP? p.114 - What are the cost/benefit issues in running a DHCP server instead of using static networking? p.115 - What is the usual way for a Linux DHCP server to be started? p.116 - Where is the DHCP server config file kept? p.117 - What is the purpose of a DHCP "leases" file? p.117 - True/False: you edit the DHCP leases file to configure DHCP. p.117 - What does DHCP "dynamic address assignment" mean? p.118 - True/False: a client receiving an address via dynamic DHCP usually keeps the same address if it isn't powered off for very long. p.118 - What is the purpose of a DHCP "subnet" declaration? p.121 - What is the purpose of a DHCP "range" declaraion? p.122 - What does DHCP "static address assignment" mean? p.122 - Why would you want DHCP to assign a fixed IP address to a machine? p.123 - True/False: dynamic DHCP may change a client's IP address in mid-session. p.123 - How do you configure the DHCP server to always assign the same IP address to the same hardware? p.123 - What Linux command shows you the MAC address of your active (up) network interface card(s)? Remote login and Configuring SSH - ALN Chapter 13, p.321 -------------------------------- - True/False: Remote login tools directly permit X11 graphical programs to run. p.309 - Rank ssh, rlogin, and telnet in order from most to least secure. p.310 - True/False: the telnet protocol sends your password in clear text over the network. p.320 - True/False: a telnet session itself is encrypted once you log in. p.320 - What kind of protocol is SSH? p.321 - What is the name of the non-commercial open source SSH package used in most Linux distributions? p.322 - True/False: the open source SSH and the commercial SSH cannot connect to each other. p.322 - What are the names of the three software packages needed to install a full open source SSH client and server on a Linux system? p.323 (Text Errata Note: "-client" should be spelled "-clients".) - True/False: SSH allows you to forward ports across your encrypted connection. p.323 - True/False: the scp program encrypts the login but not the data. p.323-324 - How is the SSH server usually started in Linux? p.324 - What is the absolute pathname of the script used to start the SSH server? (Go look!) - What is the actual name of the running SSH server started by the script? (What is the absolute pathname of the SSH server program?) - What configuration has to happen before you can run the SSH server for the very first time? p.325 - What are the key types of the key files that the Mandrake Mini system SSH start-up script generates before starting the SSH server? (Go look!) - What happens to client connections if you re-generate (overwrite) the encryption keys on your server? p.325 - What is the absolute pathname of the SSH server config file? p.325 - What is the absolute pathname of the SSH client config file? p.325 - What happens the first time you use an SSH client to connect to a server? p.328 - What happens at the client end when the key for a server changes? p.328-329 - How can you force an SSH client connection to a server if the key file has changed? p.329 Configuring POP3 - ALN Chapter 11 ---------------- - What is the difference between a "Push" and a "Pull" mail protocol? p.257 - True/False: a pull mail server can operate without a working push server. p.257 - An enterprise mail system receives email (delivered via the SMTP push mail protocol). Describe two ways that office users can read this email. p.258 - When is running a pull mail server useful? p.259 - What happens if the push mail server (SMTP server) on a pull mail machine (POP3 server) fails? p.259 - Describe what "relay" means in a push mail protocol. p.259-260 - True/False: a push mail server needs a larger disk than a pull mail server. p.261 - True/False: pull mail servers are used for retrieving mail. p.261 - True/False: push mail servers are used for sending mail. p.261 - True/False: You must use the same host name for your push and pull mail servers. p.261 - Describe briefly how POP and IMAP servers handle their email store. p.262, p.266-267 - True/False: POPmail requires more storage and bandwidth than IMAP. p.262, p.266-267 - True/False: default POP and IMAP mail servers carry userids, passwords, and email safely in encrypted form. p.267 - True/False: most POP servers require no configuration. p.267 - True/False: most POP/IMAP servers run under a "super-server" such as inetd/xinetd. p.269 The inetd/xinietd "super-servers" - ALN p.89-99 --------------------------------- - How does a super-server work? p.89 - Outline the costs/benefits to using a super-server instead of running many individual servers. p.89 - Suppose the super-server and each of five other servers controlled by the super-server take 1MB of memory each. (1) How much memory is in use when none of the other servers are being used? (2) How much memory is in use if all the other servers are being used? - If we start the five other servers (e.g. from SysV start-up scripts) without running the super-server, (3) how much memory is in use if none of the five servers are being used? (4) How much memory is in use if all of the five servers are being used? (Hint: same answer) - What is the network function of TCP Wrappers? p.92 - Name the two config files used by TCP Wrappers. p.92 - What daemons are listed in the Mandrake Mini tcpwrappers files? (Go look!) - Where does the xinetd super-server keep its main config file? p.96 - Where does the xinetd super-server keep its supplementary config files? p.96 - How many supplementary xinetd config files are installed in your Mandrake mini system? (Go look!) - For all the supplementary xinetd config files, how many are enabled/disabled? (Go look! "grep" is your friend) p.97 - How do you tell xinetd to reload/reread its configuration files? p.98 The last lines of output of "chkconfig --list" show the xinetd servers statuses under the heading "xinetd based services". Configuring SMTP (Postfix) - ALN p.507 ---------------- Linux offers several SMTP (Mail Transfer Agent - MTA) programs. (The ALN text calls these mail delivery or "Push" protocols [p.477].) The most well-known is the ancient "sendmail" program whose configuration file "has traditionally been described as looking like an explosion in a punctuation factory". Mandrake Linux uses the more modern Postfix MTA. - True/False: an SMTP server is known as a Mail Transfer Agent ("MTA"). p.478 - What is the purpose of an MTA? p.478 - True/False: most Linux systems install an SMTP server by default. p.479 - Describe the traditional Unix "mbox" mail format used by sendmail/Exim/Postfix? p.480-481 - Describe the new "maildir" mail format used by qmail. p.481 - What is a DNS "MX" record? p.481 The "host -t mx " command can list MX records for . - What are the MX records for algonquincollege.com? for idallen.org? - What purpose do the sequence numbers have in a set of MX records? p.482 - Describe the difference between "envelope headers", "message headers", and "message data". p.482-483 - True/False: the message headers are optional and can be omitted. p.483 - True/False: the envelope headers must match the message headers. p.484 - What is a big advantage of the Postfix config file over sendmail's config file? p.507 - Which Postfix config file is usually modified (absolute path)? p.508 - Text Errata Note: The fully commented postfix config file is now named "main.cf.dist". The main.cf file contains only the few lines that change the default postfix operation; read main.cf.dist for help. The file main.cf.default shows what default values are compiled into postfix. p.508 - What Postfix file contains system-wide mail aliases? p.508 - How do you generate the binary .db files from the text files? p.508 - How is the Postfix server started/stopped? p.508-509 - Does the start-up script for postfix run the postalias command? (Go look!)