A + Supplemental Guide
V0822
By studying the information found in this document,
you will be better prepared for the exam.
The four topics that will be covered hereafter are as follows:
1.
2.
3.
4.
Port numbers and protocols
Windows commands
UNIX/LINUX commands
RAID (Redundant Array of Independent Disks)
1. PORT NUMBERS & PROTOCOLS
The purpose of protocols: Protocols are a set of rules and procedures that allow two computers to
communicate over a network. Examples include HTTP, DNS, and FTP. Each protocol has its own rules and
unique purpose.
The purpose of port numbers: When two computers communicate, they will tag their messages with port
numbers. The numbers indicate what protocol is being used and allow any computer to have multiple
conversations simultaneously (aka multiplexing).
PORT #
PROTOCOL
DEFINITION / FUNCTION
20/21
FTP
22
SSH
23
TELNET
25
SMTP
53
DNS
67/68
DHCP
69
80
110
TFTP
HTTP
POP
File Transfer Protocol. Used to reliably transfer large files. Port 20 for data, 21
for authentication and file browsing.
Secure Shell. Provides an encrypted tunnel to access a remote devices
command prompt. Secure!
Provides access to a remote devices command prompt, but does not have any
encryption. Very insecure!
Simple Mail Transfer Protocol. Used to send emails to an email server, or mail
between servers. Not encrypted by default.
Domain Name System. Used to look up domain names like www.example.com
and find out what IP address they are using.
Dynamic Host Configuration Protocol. Used to assign dynamic IP addresses to
computers when they first join the network.
Trivial File Transfer Protocol. Similar to FTP, but only suitable for small files. It
does NOT offer encryption or any form of authentication.
Hypertext Transfer Protocol. Used to retrieve/view websites. No encryption.
123
NTP
137-139
NBT
143
IMAP
161/162
SNMP
443
HTTPS
445
SMB
993
IMAPS
995
POPS
3389
RDP
Post Office Protocol. Used to download emails from an email server, not for
sending. No encryption.
Network Time Protocol. Used to synchronize the time configured on the
computers across a network.
Net BIOS. Used by computers to identify other systems by name on a single
network and to send/share files between devices. Can’t operate over the
internet by itself.
Internet Message Access Protocol. Used to view an email that exists on an
email server. An alternative to POP. No encryption.
Simple Network Management Protocol. Used to send logs over a network and
to remotely manage network hardware. Only V3 is secure.
The encrypted version of HTTP. It is encrypted through SSL or TLS. It requires
the use of certificates on the web server.
Server Message Block. Much like Netbios, but more advanced. Operates
through IP addresses, so it can provide Netbios functions over the internet.
The encrypted version of IMAP. It is encrypted through SSL or TLS. It requires
the use of certificates on the email server.
The encrypted version of POP. It is encrypted through SSL or TLS. It requires
the use of certificates on the email server.
The Remote Desktop Protocol. Native to Windows, it allows one user to access
another computer’s desktop (GUI/graphical user interface) remotely.
Encrypted.
2. WINDOWS COMMANDS
COMMAND
PING X
where X, the target, is an IP
address or fully qualified
name, like
www.example.com
TRACERT X
Where X, the target, is an IP
address or fully qualified
name, like
www.example.com
IPCONFIG
NSLOOKUP X
Where X is a fully qualified
name or IP address
Suggestion: Try them out on your own! You can
reach the command prompt by searching for “cmd”.
FUNCTION
Used to test connectivity TO and FROM a target device. The source computer
sends out an “echo request” to the target, who will reply back with an “echo
reply” if they received the message. If the source receives an echo reply, this
confirms bi-directional communication over the network. Also, if you ping by
name, it will allow you to see if DNS is working.
Used to show all of the routers/servers between you (the source) and the target
(destination). This is similar to PING but now you can see all of the routers along
the way. This helps troubleshoot if there is a problem between two points.
By itself, this command shows you your current IP address, network mask, and
default gateway (the router that connects you to other networks or the internet).
Add any of the following to the end of Ipconfig to get different results:
/ALL - shows all basic info, plus MAC address, IP lease time, and DNS/DHCP
servers.
/RELEASE - gives the IP address BACK to the DHCP server
/RENEW - asks DHCP for a refresh on the IP lease time
/DISPLAYDNS - shows all DNS info in our cache
/FLUSHDNS - clears all DNS info in our cache
If you enter a name, such as www.google.com, you will perform a forward
lookup/query on port 53 through DNS, and receive an IP address as a result.
If you enter an IP address, such as 8.8.8.8, you will perform a reverse
lookup/query on port 53 through DNS, and receive a fully qualified name as a
result.
Netstat
Short for Network Statistics. This will show you all of your active network
connections. If you use any of the following commands after netstat, it will give
you more information:
-a (short for ALL) now it will show you open ports that aren’t even being used,
usually called listening ports.
-n now it will show all the IP addresses instead of only names.
-o now it will show what processes opened this connection. This function requires
admin privileges.
NBTstat
Short for Network Bios Statistics. This will show you information about users and
groups that have been seen on the local network, communicating through
netbios.
Bootrec /fixmbt
This command is only used in the recovery command prompted when a hard
drive has a corrupted boot record. The command is short for “fix the master
boot”. You will need this if the Windows OS can’t be found on the hard drive
due to a corrupted boot record.
3. UNIX/LINUX COMMANDS
UNIX COMMANDS ARE CASE SENTITIVE BY DEFAULT
COMMAND
FUNCTION
ls
List. It will display a list of all files in the current folder, or in the target folder if specified.
For example, “ls /record/finance/*.xls” would list all of the files that end in .XLS, within the
finance folder, inside of the record folder.
pwd
Print Working Directory. It will show you what folder you are currently in.
cd
Change Directory. This allows you to change to whatever directory you specify. (This also
works in Windows!)
cp
Copy. This command copies a file. Proper syntax is “cp [file to be copied] [destination].”
mv
Move. This command moves one or more files or directories from one location to another.
Proper syntax is mv [options] [source] [destination].
rm
Remove. This deletes the specified files or folders.
grep
passwd
A very versatile searching utility, Grep can search any plain-text data set for a specific
“regular expression” which is a fancy way of saying search for a predefined string of
characters. Syntax is grep [options] [pattern] [file name].
Example: grep “find_this_pattern” file123. This would display any line in document “file
123” that contained “find_this_pattern”.
Password. This command is used to change a user’s password.
sudo
Superuser Do. This command would be put in front of any command that we want to
execute with superuser (elevated/restricted) privileges. Most systems will request a
password be entered and checked before proceeding.
chmod
Change Modes. This command is used to change the permissions on an object (file).
chown
Change Owner. This command assigns a new owner to an object (file) and this includes
granting all of the permissions/privileges that would be associated with ownership.
Requires root permissions to use, so it should be proceeded by sudo.
ps
Processes. Displays a list of all currently running process (programs/services) for the user.
kill
Sends a signal to a running process, to by default, terminate (close). However, kill can be
used to send other instructions if done properly!
ifconfig
Interface Configure. Similar to ipconfig in Windows, it shows the current configuration of
the network interface card.
cat
Concatenate. Reads a file and prints contents to the screen.
dig
Domain Information Groper. Similar to nslookup in windows, it can be used to
communicate with a DNS server.
4. RAID (Redundant Array of Independent Disks)
Two things are true of all hard drives. They have a maximum read and write speed, and they will inevitably fail.
When faced with this truth, system designers will often combine hard drives together to increase performance
(faster read/write) and or provide redundancy. There are five raid configurations worth knowing for this exam.
RAID ZERO
How it is performed: Data is “striped” across all of the
drives in the array. If you used two drives, half of the file
would be on one drive, half would be on the other.
Minimum number of disks: TWO
Calculating the size: Add them all together.
Benefits: Speed and space, but not redundancy.
Fault tolerance: none (zero). If any disk fails,
all data is lost and unrecoverable.
RAID ONE
Minimum number of disks: TWO
How it is performed: Data is “mirrored” across all of the
drives in the array. If you used two drives, any data that is
put on one drive will be copied (mirrored) onto the other.
Benefits: fault tolerance (redundancy).
RAID FIVE
Calculating the size: The size of only the
smallest disk in the array.
Fault tolerance: One of the disks can fail and
everything can keep on running.
Benefits: Speed and fault tolerance (redundancy).
Minimum number of disks: THREE
Calculating the size: Add them all together
and subtract one drive from the total.
Fault tolerance: One of the disks can fail. As a
result, the remaining two disks will be slow
until the missing drive is replaced.
RAID SIX
Minimum number of disks: FOUR
How it is performed: Data is “striped” across two drives,
and the third drive will hold a parity bit. The parity bit is
like the answer to a math question that allows any one of
the drives to fail and be replaced later.
How it is performed: Data is “striped” across two drives,
and the other two drives will hold a parity bit. The parity
bits are like the answer to a math question that allows any
two of the four drives to fail and be replaced later.
Calculating the size: Add them all together
and subtract two drives from the total.
Benefits: Speed, and more redundancy than RAID 5.
Fault tolerance: Two of the disks can fail. As a
result, the remaining two working disks will be
very slow until the missing ones are replaced.
RAID TEN (nested)
Minimum number of disks: FOUR
How it is performed: Data striped across two drives, and
then mirrored (copied) to the other two. This is known as
RAID nesting, as we are basically performing RAID 0 and
then RAID 1.
Benefits: Speed of RAID 0 and the redundancy of RAID 1.
Calculating the size: Add them all together
and divide in half.
Fault tolerance: one or two, depending on
which drives fail.