Linux Administration

Front 1

packets are layered by_____, with the lowest layers coming ____.

Back 1

protocol

first

Front 2

When a host’s network card receives a packet, it first checks to see if it is supposed ________.

Back 2

to accept the packet.

Front 3

This is done by looking at the destination addresses located in the
________.

Back 3

packet headers

Front 4

If the network card thinks that it should accept the packet, it keeps a copy of it in its memory and generates
an _________.

Back 4

interrupt to the operating system.

Front 5

Upon receiving this interrupt, the operating system calls on the device driver of the ______ to process the new packet.

Back 5

network interface card (NIC)

Front 6

The device driver copies the
packet from the NIC’s memory to the system’s memory. Once it has a complete copy, it can examine the packet and ______.

Back 6

determine what type of protocol is being used.

Front 7

Note that the stack does not begin processing the packet immediately. This is because
the operating system may be doing something important that it needs to finish before _______.

Back 7

letting the stack process the packet.

Front 8

Since it is possible for the device driver to receive
many packets from the NIC quickly, a _____ exists between the driver and the stack software.
The _____ simply keeps track of the order in which packets arrive and notes where
they are in memory. When the stack is ready to process those packets, it grabs them from
the _____ in the appropriate order.

Back 8

queue

queue

queue

Front 9

As each layer processes the packet, appropriate headers are removed. In the case of a
TCP/IP packet over Ethernet, the driver will strip the _____ headers, IP will strip the
_____, and TCP will strip the ______. This will leave just the data that needs
to be delivered to the appropriate application.

Back 9

Ethernet
IP header
TCP headers

Front 10

The TCP/IP model is an architectural model that helps describe the components of
the TCP/IP protocol suite. It is also known by other names:

Back 10

Internet reference model,
Department of Defense (DoD) ARPANET reference model.

Front 11

The ISO’s OSI (Open Systems Interconnection) model is a well-known reference
model for describing the various abstraction layers in networking. The OSI model has
seven layers:

Back 11

Physical layer,
Data Link layer,
Network layer,
Transport layer,
Session layer,
Presentation layer,
Application layer.

Front 12

This Layer describes the actual medium on which the data flows. In a
network infrastructure, a pile of Cat 5 Ethernet cable and the signaling protocol are considered ______

Back 12

the Physical layer.

Front 13

____ used to describe the Ethernet protocol.The difference
between the OSI’s view of Layer 2 and Ethernet is that Ethernet only concerns itself with
sending frames and providing a valid checksum for them.

Back 13

Ehternet

Front 14

The purpose of the checksum
is to allow the receiver to validate whether the data arrived as it was sent. This is done
by computing the ______ of the packet contents and comparing
them against the checksum that was provided by the sender.

Back 14

Cyclic Redundancy Check (CRC)

Front 15

If the receiver gets
a corrupted frame (that is, the checksums do not match), the packet is dropped here.
From Linux’s point of view, it should not receive a packet that the _______ knows is corrupted.

Back 15

network interface card

Front 16

OSI model formally specifies that Layer 2 should handle the automatic
retransmission of a corrupted packet, Ethernet does not do this. Instead, Ethernet relies
on _____to handle retransmission.

Back 16

higher-level protocols (TCP in this case)

Front 17

Ethernet’s primary responsibility is simple:

Back 17

Get the packet from one host on a local
area network (LAN) to another host on a LAN.

Front 18

_____ the layer at which the Internet Protocol (IP) exists.
IP is wiser to the world around it than Ethernet.

Back 18

IP or Network Layer

Front 19

_____ understands how to communicate
with hosts inside the immediate LAN as well as with hosts that are not directly connected
to you. This
means that an IP packet can make its way to any other host, so long as a path (route)
exists to the destination host.

Back 19

the IP

Front 20

The reason why ____ does not provide any more features than those of a simple
transport protocol is that it was meant to be a foundation for other protocols to rest on.

Back 20

IP

Front 21

Transmission Control Protocol (TCP) and User Datagram
Protocol (UDP) are mapped to the ______.

Back 21

Transport layer.

Front 22

______ actually maps to this OSI layer
quite well by providing a reliable transport for one session

Back 22

TCP

Front 23

In addition to sessions, _____ handles the ordering and retransmission of packets. If
a series of packets arrives out of order, the stack will put them back into order before
passing them up to the application. If a packet arrives with any kind of problem or goes
missing altogether, ____ will automatically request the sender to retransmit.

Back 23

TCP

Front 24

Finally, ____
connections are also bidirectional. This means that the client and server can send and
receive data on the same connection.

Back 24

TCP

Front 25

____, by comparison, doesn’t map quite as nicely to OSI. While____ understands the
concept of sessions and is bidirectional, it does not provide reliability. In other words,
_____ won’t detect lost or duplicate packets the way TCP does.

Back 25

UDP

Front 26

Technically, all applications that
use TCP or UDP sit here; however, the marketplace generally calls _____ traffic Layer 7.

Back 26

Hypertext Transport
Protocol (HTTP)

Front 27

______ is a bit of an odd bird and is not commonly associated
with any layer. It sits squarely between Layer 4 (TCP) and Layer 7 (Application, typically
HTTP), and can be used to encrypt arbitrary TCP streams.

Back 27

Secure Sockets Layer (SSL)

Front 28

In general, ____ is not
referred to as a layer. You should note, however, that _____L can encrypt arbitrary TCP connections,
not just HTTP.

Back 28

SSL

Front 29

Many protocols, like Post Office Protocol (POP) and Internet
Message Access Protocol (IMAP), offer _____ as an encryption option, and the emergence
of SSL-virtual private network (VPN) technology shows how SSL can be used as an
arbitrary tunnel.

Back 29

SSL

Front 30

To date, there is no
framing protocol for ____ that runs on top of TCP directly

Back 30

XML

Front 31

_____ data uses existing
protocols, like HTTP, Dual Independent Map Encoding (DIME), and Simple Mail
Transfer Protocol (SMTP).(DIME was created specifically for transmitting ____.)

Back 31

XML

Front 32

Every ____ packet contains a type that tells the recipient what the nature of
the message is. The most popular type is “Echo-Request,” which is used by the
infamous ping program. When a host receives the ____ “Echo-Request” message,
it responds with an ___ “Echo-Reply” message. This allows the sender
to confirm that the other host is up, and since we can see how long it takes the
message to be sent and replied to, we get an idea of the latency of the network
between the two hosts.

Back 32

Internet Control Message Protocol (ICMP)

Front 33

Layer 8 typically refers to the _____

Back 33

“political” or “financial” layer,
JOKE!! HAHAHA

Front 34

_____ contains three entries: the destination address, the source
address, and the packet’s protocol type. Ethernet addresses—also called Media Access
Control (MAC) addresses

Back 34

Ethernet header

Front 35

[root@serverA ~]# tcpdump -e

does what?

Back 35

Shows Ethernet headers in network

Front 36

This command does what:

[root@serverA ~]# tcpdump -e -n

Back 36

where the -n option tells tcpdump to not do name resolution.

Front 37

Explain:

[root@serverA:~]# tcpdump -v -t -n -c 2 ip

Back 37

-v shows everthing in tcdump ip header
-c you can ask tcdump to stop after fixed number of packets

-n tells tcdump not to remane resolution

-t time stamp parameter

Front 38

TCP flag:

urg
ack
psh
rst
syn
fin

Back 38

urg - implies there is urgent data in package
ack - Acknowledgment of successfully received data.
psh - Request to immediately process any received data.
rst - Immediately terminates the connection.
syn - Request to start a new connection.
fin - Request to finish a connection.

Front 39

____ supports the concept of a connection

Back 39

TCP

Front 40

____ goes through a three-way handshake for every connection that it opens up.

The first packet is sent by the host that wants to open the connection with a server.

The second packet is sent from the server to the client. This packet contains two TCP
flags set: SYN and ACK.

the third packet goes from the client to the server. It has only the ACK bit set
in the TCP flags for the purpose of acknowledging to the server that it received its SYN

Back 40

TCP