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62 Cards in this Set
- Front
- Back
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What is a network? |
A network is an interconnected collection of computers for sharing and retreiving information and resources. |
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What is a LAN? |
A local area network which connects devices over a short distance. Usually implemented as one subnet with less than 256 endpoints. |
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What is a WAN? |
A wide area network that connects devices over a large distance. Generally, it interconnects multiple LANs. Many computers, and usually more than one subnet. Not owned by one individual. |
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Personal Area Network |
Bluetooth connection between cell phones and headsets |
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Storage Area Network |
A network solely for storage. CyFiles for example. |
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T/F One machine can be connected to multiple LANs |
True |
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What is network topology? |
How everything is connected, usually drawn abstractly as graphs. |
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What is the Client/Server Model? |
A computing model in which tasks are partitioned into two parts: - Clients request services - Servers provide services Also used on single systems (X server, microkernels, etc) |
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Describe the life of a server program |
1. Listen for requests 2. When a request comes, handle it - Provide the requested service (if allowed) - Often, this means "start a process"... 3. Loop |
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Is a server program usually a daemon? |
Yes, a daemon sits and runs continually. Servers can also be clients so that they can request different services. Can be local or remote to the client. |
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What is a server machine? |
A machine dedicated to solely running server programs. They are usually more powerful than regular machines and normally have redundant components. May be part of private and public networks, and clustered together. |
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What is a client and give examples of typical client requests |
Make requests to server - Content, services, etc. For example, web browsers are client processes running on a client machine. |
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What is the command sshd and what does it do? |
sshd is a server program that "runs shell commands" On the client side, it allows a client to use ssh and access the server's shell + data anywhere in the world. |
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Explain a communication layer |
Partitions of communication, which provide an abstract view of the network. Each has its own protocol, and they are bundled into the "protocol stack/suite" Each layer will encode transmitted data and decode received data. Conceptually works like a pipeline. |
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What is the Open Systems Interconnection model? |
Abstract model specified by ISO with 7 layers; application, presentation, session - User-level transport, network - OS (usually in kernel space) data link, physical - Hardware |
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What is the job of a Physical Layer |
To physically send bits on a link between machines. |
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What is the job of a Data Link Layer? |
To send frames (fixed-length chunks of data around 1 kb) on a link between machines. Includes error correction for physical layer. |
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What is the Network Layer? |
It's job is to send variable-sized packets between machines. Must route a path through the network, choosing the best one. Also must address machines and network devices. Packet loss and delays are possible. |
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Where does the program "ping" fall into the OSI networking model? |
The network layer is responsible for pinging packets back and forth between machines. |
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What is an IP? |
Internet Protocol: the "network layer address" that are names for network devices. Fully-qualified domain names may be used instead, i.e. cs.iastate.edu and converts the name through a DNS server to a numeric IP address. |
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How does a machine or network device get its IP address? |
Statically: the sys-admin chooses a hardcoded IP address, it is fixed. Dynamically: machine asks someone else for an IP address. DHCP handles this. More scaleable than static IP configurations. |
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Explain the traceroute utility |
It is used to trace on possible route to the destination address and shows transit delays of packets between stages. ex: $ tracerout -q 1 -w 1 129.168.1.1 |
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What is the job of the Transport Layer? |
To transfer data between computers
This layer deals with breaking data into network packets, controlling the flow of data, and handling errors such as packet-loss. |
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Compare UDP and TCP |
UDP: User Datagram Protocol - Data is sent in fixed-size datagrams, and does "best-effort" delivery only. - A very thin wrapper around packets. TCP: Transmission Control Protocol - Data is viewed as a stream - Guaranteed delivery of packets - A conceptual giant, reliable pipe of data. |
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T/F Client and server processes must agree on a single protocol (UDP, TCP) |
True; some services use UDP and some use TCP, but both the client and the server must use UDP or both use TCP when transferring the data. |
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What is the Session Layer's job? |
To deal with communication sessions between computers, initializing connections, removing connections, managing connections during transfers, error handling to recover or close failed sessions |
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What is Full Duplex vs Half Duplex session layer? |
Full Duplex: may send and receive Half Duplex: may either send or receive, not both |
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T/F TCP includes session control |
True, so TCP is in the Session Layer |
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T/F Multiple processes can be listening on one port |
False! Each port can have at most 1 process listening. Certain ports are reserved, i.e. 22 is reserved for ssh. |
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What is a network firewall? |
A mechanism used to ignore certain network packets |
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In what layer(s) can a firewall be configured on? |
The session layer - drop packets by port number Transport layer - drop packets via TCP vs UDP Network Layer - drop packets based on IP addr |
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What is the job of the Application Layer |
To interact with the end user. Handles top-layer client/server protocol HTTP, SMTP/IMAP, DNS/DHCP, SSH/RDP, FTP, SSL, LDAP, SNMP |
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What organization provides the httpd service? |
Apache Software Foundation, provides a HTTP server protocol to the user. (Man pages will be provided on exam) |
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What is the utility curl? |
It will copy a URL, which transfers data from or to a server. Basically just displays the content of an HTTP url by downloading it and displaying it via command line. |
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By good practice, what do the following network interfaces control? eth0 em3 p3p1 |
eth0 - ethernet interface em3 - embedded interface (slot 3) p3p1 - PCI slot 3 ethernet port 1 |
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List some of the essential entries to an ifcfg-p7p1 file or similar. |
BOOTPROTO, IPADDR, NETMASK, ONBOOT, HWADDR, etc. Man pages give full list of entries. |
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What does running ifconfig -a output? |
The configuration for all network devices |
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What configuration file would I use to specify a specific IP address to be used as a DNS server? What config file would I use to specify the IP address of the network's gateway? (List the full path for both) |
/etc/resolv.conf for DNS server IP /etc/sysconfig/network for network gateway IP |
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What does the /etc/hosts config contain and what is it used for? |
A list of IP addresses and associated host names Linux looks here before asking DNS servers Useful to set up a few local host names or to set up your own custom DNS server |
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What does the service iptables do and what is it used for? |
Service handles IP packet filtering rules, but only sets the rules up. Handles NAT and Routing Firewall configuration uses iptables, etc. |
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When is Ring Topology used? |
2 or more hosts arranged in a circle, data travelling in one direction, or two rings for bi-directional. Used for Fiberoptic cable |
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What is a Mesh Network? |
Central nodes connected to one or more other nodes. Data must be routed to destination. Widely used for wireless networks without central base stations. |
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Identify and describe what TTL is |
Time to Live - the maximum lifetime of a packet - keeps packets from going in circles forever In practice, it is the maximum "hop count" based on the number or routers. More routers = less TTL |
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What is NAT? |
Network Address Translation: (IP Masquerading) A gateway router intercepts packets from private network, rewrites them and spoofs the gateway's real address and sends them off Upon receiving of packets, it reverses the rewrite |
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What are the benefits of using NAT? |
- Make private networks useful by allowing them to connect to the public internet - Slowed consumption of IP addresses - Gives security and natural firewalling, have to hack gateway before actual network |
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What is Samba? |
Also known as CIFS, it allows Linux machines to be clients and servers in a "Windows Network" |
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Configure autofs to mount a samba filesystem automatically on boot |
/etc/auto.master: "/shares/smb /etc/auto.smb" /etc/auto.smb: "SambaFS -fstype=cifs,rw,file_mode=0777,dir_mode=0777 172.168.1.1://samba/share" |
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Add a user alice with password alicepw Remove a user bob w/ password bobpw Change user alice's name to chuck |
# useradd -d /data/alice alice [enter alicepw for passwd] # userdel -r bob #usermod -l chuck alice |
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Create a group called network_dev and add user alice to it. Change bob's primary group to network_dev Add group network_dev to chuck w/o deleting his other groups |
# newgrp network_dev # usermod -G network_dev alice # usermod -g network_dev bob # usermod -a -G network_dev chuck |
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Show a line in /etc/passwd that assigns a user alice with an ID of 512 and group id of 101. Her full name is Alice Gnu and her home directory is /home/alice. She should also have access to the default shell. |
alice:x:512:101:Alice Gnu:/home/alice:/bin/bash |
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Give the contents of hosts.allow and hosts.deny configs that allow localhost, ssh access from anywhere except 44.22.11.x, and portmapper access from the local subnet (192.168.42.x) |
/etc/hosts.allow ALL : localhost sshd : 44.22.11. : deny sshd : ALL portmap : 192.168.42. /etc/hosts.deny ALL : ALL |
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What is NFS and what are its uses/benefits? |
Network File System - allows servers to export or share a folder and clients to mount said exported folder. Supports UNIX filesystems, and permissions + file owners and groups can be exported. |
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Configure an NFS client to mount the folder export from server to /mnt/nfs/share. (no autofs) |
# service portmapper enable # service portmapper restart # mount -t nfs server:/export /mnt/nfs/share |
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Set up an NFS Server that persists on reboot for servers inside subnet 10.0.0.1 through 24. Mount to /home with read and write permissions. |
# vim /etc/exports /home 10.0.0.1/24(rw, sync) # chkconfig rpcbind on # chkconfig nfs on |
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Configure an NFS Client for the server (10.0.0.1/24 mounted to /home with read and write perms). Use autofs to mount the directory on boot. (mount with name nfs_home on /export) |
# chkconfig rpcbind on # mkdir /export # vim auto.master /export /etc/auto.nfs --timeout 60 # vim auto.nfs nfs_home -rw,soft 10.0.0.1:/home # service autofs enable && service autofs restart |
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What is NIS and what are its benefits? |
Network Information Service that keeps info synchronized among hosts. Allows file data to be transferred over the network. Old and unsecure |
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Set up an NIS server and edit the server configuration if necessary. Set domain name to Server252. Allow traffic from only the local machine and 10.0.0.0/24 and initialize it as the primary NIS server. |
# service enable ypserv # service restart ypserv # vim /etc/sysconfig/network NISDOMAIN=Server252 # vim /var/yp/securenets 255.255.255.255 127.0.0.1 255.255.255.0 10.0.0.0 # /usr/lib/yp/ypinit -m |
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Configure an NIS client to connect to 10.0.0.1 with a domain name of Client252. |
# service ypbind enable # vim /etc/yp.conf domain Client252 server 10.0.0.1 # vim /etc/sysconfig/network NISDOMAIN=Client252 # service ypbind restart |
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What is DHCP and why use it? |
DHCP or the service dhcpd is easy to set up on both servers and clients. It is easy to move clients, and network changes are centralized. DHCP is used to tell a client what IP address, subnet mask, gateway, dns server to use, etc. It uses UDP broadcast packets. Server statements that are useful (/etc/dhcpd.conf): default-lease-time <sec>; max-lease-time <sec>; and more. Man pages have more info. |
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What is DNS? |
Domain Name System. DNS finds IP addresses for host names (google.com, etc). Networks consist of DNS zones, portions of domain name space each with an authoritative DNS server. It is the Internet's "phone book" DNS is a huge database, using hierarchical tree structure where each node is a domain, the top being the root domain. In this tree, a resolver on client side tries to complete unqualified names. ie relative paths or "." and configured /etc/resolv.conf formatted: "search dom1 dom2 ..." |
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Explain iterative vs recursive DNS queries |
Iterative query - client sends a domain name, server does not query other servers, returns either ip address for domain or name of another dns server. Recursive query - client sends domain name, server returns ip address for domain and may query other servers to get the ip. |
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Explain the differences between master and slave dns servers. |
Master server is authoritative, holds master copy of zone data, queries answers based on zone file, and is only iterative. Slave server is authoritative, obtains zone data from another server, and may be recursive. |
