SEMESTER 1 Final Study Guide

Drippy Sweet Pancakes For Breakfast (Encapsulation)

Please Do Not Throw Sausage Pizza Away (OSI model) Never Ingest Tainted Apple (TCP/IP model)

* Make sure you know the basic functions of each layer for the above models.

* Router is residing on which layer of OSI model?

* Switch is residing on which layer of OSI model?

* When a connectionless protocols is used to send mission critical data (such as TFTP protocol),

how does the TFTP supplement this connectionless protocol and guaranty the delivery of all the

mission critical data?

* When a data going through the encapsulation process from the top to the bottom, it creates port

number and then encapsulation it inside the packet. Then packet creates IP address and then

encapsulated in the frame. Then frame create the MAC address and then turn it into bits.

* When a data going through the reverse encapsulation process from the bottom to the top, it

will only accept and pass the frame to the network layer, if the MAC address matches with the

host’s MAC address (or match the broadcast address). Also, it will only accept and pass the

packet to the transport layer, if the IP address matches with the host’s IP address (or match the

broadcast address).

* Can you identify what layer of the OSI each of the following diagrams is located? You need to

be able to identity some of the fields from each of the diagram that we spend a lot of time to go

over them in the class.

* Make sure you know all the technical name of all the devices and all the protocols needed for

each link?

- MUA SMTP MTA SMTP MTA MDA POP MUA (Tony: Know the sequence.)

* The http://www.cisco.com/index.html example

• http (the protocol or scheme)

• www.cisco.com (the server name)

• A web page named index.html on a server.

* Port numbers:

Well Known Ports (Numbers 0 to 1023) - These numbers are reserved for services and

applications.

Registered Ports (Numbers 1024 to 49151) - These port numbers are assigned to user

processes or applications.

Dynamic or Private Ports (Numbers 49152 to 65535) - Also known as Ephemeral Ports,

these are usually assigned dynamically to client applications when initiating a connection.

Here is another one that I think the answer key is wrong again. The question asks

which range of the port dynamically assigned to the client’s when initiated a

connection to the server, but the range 49152 to 65535 is not one of the choices.

Therefore, you should pick 1024 to 49151 as the correct answer.

Peer-to-Peer Networks

– In a peer-to-peer network, two or more computers are connected via a network

and can share resources (such as printers and files) without having a dedicated

server.

– Every connected end device (known as a peer) can function as either a server or a

client.

* The Client-Server Model

– the device requesting the information is called a client

– the device responding to the request is called a server.

– One example of a client/server network is a corporate environment where

employees use a company e-mail server to send, receive and store e-mail.

* The primary functions specified by all Transport layer protocols include:

– Segmentation and Reassembly

– Conversation Multiplexing

* In addition to the basic functions of data segmentation and reassembly, some protocols at the

Transport layer provide:

– Connection-oriented conversations

– Reliable delivery

– Ordered data reconstruction

– Flow control

* User Datagram Protocol (UDP)

– It providing for low overhead data delivery.

– The pieces of communication in UDP are called datagrams.

– These datagrams are sent as "best effort".

* Transmission Control Protocol (TCP)

– TCP is a connection-oriented protocol.

– TCP incurs additional overhead to gain functions.

– Additional functions specified by TCP are the same order delivery, reliable delivery, and

flow control.

* The TCP and UDP based services keep track of the various applications that are

communicating. Both TCP and UDP have header fields that can uniquely identify these

applications.

These unique identifiers are the port numbers.

* Port Addressing: netstat command

Sometimes it is necessary to know which active TCP connections are open and running

on a networked host.

Netstat is an important network utility that can be used to verify those connections.

Netstat lists:

– the protocol in use,

– the local address and port number,

– the foreign address and port number,

– the state of the connection.

* You need to know how the segment sequence number and acknowledgement number are used

to confirm receipt of the bytes of data in the segments.

For example: The telnet example covered in the lecture.

– The host on the left is sending data containing 10 bytes of data and a sequence

number equal to 1 in the header.

– The on the right receives the segment and determines that the sequence number is

1 and that it has 10 bytes of data.

– When the sending host on the left receives this acknowledgement, it can now send

the next segment starting with byte number 11.

* IP Address:

32 bits

Each end device must have a unique address

The Internet consists of millions of hosts, each of which is identified by its unique

Network layer address.

Layer 3 addresses supply the network portion of the address. Routers forward packets

between networks by referring only to the part of the Network layer address that is

required to direct the packet toward the destination network

* What are the characteristics of “network layer address” (or some people call it network

address)?

Routers forward packets between networks by referring only to the part of the Network

layer address that is required to direct the packet toward the destination network.

Network layer addressing schemes are hierarchical.

The network address indicates the network on which each unique host address is located.

* A router makes a forwarding decision for each packet that arrives at the gateway interface.

This forwarding process is referred to as routing.

If a route to a destination network does not exist, the packet cannot be forwarded.

o [Tony]: Dropped the packet

* You will use the following tables for multiple questions. * 255.255.255.192 (or /26) 0 - 63 64 - 127 128 - 191 192 - 255 (with multiplier of 64) * 255.255.255.224 (or /27) 0 - 31 32 - 63 64 - 95 96 - 127 128 - 159 160 - 191 192 - 223 224 - 255 (with multiplier of 32)

* 255.255.255.240 (or /28) 0 - 15 16 - 31 32 - 47 48 - 63 64 - 79 80 - 95 96 - 111 112 - 127 And so on (with multiplier of 16)

* 255.255.255.248 (or /29) 0 - 7 8 - 15 16 - 23 24 - 31 32 - 39 40 - 47 48 - 55 56 - 63 And so on (with multiplier of 8)

* What is the subnet mask (you are allowed to use only one subnet mask) that can be used to

cover for all IP addresses from 10.16.128.0 through 10.16.159.255? * You will be presented a list of IP address and are expected to pick up: - Usable (assignable) host addresses * Study the reference table included above. - Network IP address

* Study the reference table included above. - Broadcast IP address * Study the reference table included above.

* Public and Private Addresses Public Addresses

– The majority of the addresses are public addresses.

– These addresses are designed to be used in the hosts that are publicly accessible

from the Internet.

Private addresses

– There are blocks of addresses that require no Internet access.

• 10.0.0.0 to 10.255.255.255 (10.0.0.0 /8)

• 172.16.0.0 to 172.31.255.255 (172.16.0.0 /12)

• 192.168.0.0 to 192.168.255.255 (192.168.0.0 /16)

Network Address Translation (NAT)

– With services to translate private addresses to public addresses, hosts on a

privately addressed network can have access to resources across the Internet.

* What is the subnet mask for the range of address from 10.10.128.0 through 10.10.159.255?

* 255.255.0.0: How many hosts are in this subnet? * 255.255.255.0: How many hosts are in this subnet? * 255.255.254.0: How many hosts are in this subnet? * 255.255.248.0: How many hosts are in this subnet? * 255.255.224.0: How many hosts are in this subnet?

* Testing Connectivity to Remote LAN

Ping is used to indicate the connectivity between two hosts.

Traceroute (tracert) is a utility that allows us to observe the path between these hosts.

– The trace generates a list of hops that were successfully reached along the path.

– This list can provide us with important verification and troubleshooting

information.

* Pinging the Local Loopback One case is for testing the internal configuration of IP on the local host. To perform this test, we ping the special reserve address of local loopback

(127.0.0.1). A response from 127.0.0.1 indicates that IP is properly installed on the host. This response is not, however, an indication that the addresses, masks, or

gateways are properly configured. Nor does it indicate anything about the status of the lower layer of the network stack.

* The characteristics of data link layer.

The Data Link layer prepares a packet for transport across the local media by

encapsulating it with a header and a trailer to create a frame.

Controls how data is placed onto the media and is received from the media using

techniques such as media access control and error detection

Ethernet Topology:

The first versions of Ethernet used coaxial cable to connect computers in a bus topology.

The physical topology was also changed to a star topology using hubs.

* What are the characteristics of CSMA/CD?

– All network devices that have messages to send must listen before transmitting.

– All node sees all the frames that are on the medium,

– Once a collision occurs, the other devices in listening mode - as well as all the

transmitting devices - will detect the increase in the signal amplitude.

Ethernet Unicast, Multicast & Broadcast frame:

A unicast MAC address is the unique address used when a frame is sent from a single

transmitting device to single destination device.

With a broadcast, the packet contains a destination IP address that has all ones (1s) in the

host portion. FF-FF-FF-FF-FF-FF

the switch sends the frame to all ports except the port on which the frame arrived.

Multicast addresses allow a source device to send a packet to a group of devices.

Switch forwarding is based on the Destination MAC

– The switch maintains a table, called a MAC table. that matches a destination MAC

address with the port used to connect to a node.

– For each incoming frame, the destination MAC address in the frame header is

compared to the list of addresses in the MAC table.

– If a match is found, the port number in the table that is paired with the MAC address

is used as the exit port for the frame.

* Still need to know this. You need to know where is the location of the data and it determines

what is the source MAC and destination MAC address.

* Counting broadcast and broadcast domain.

* How to count the number of subnets needed for the network?

* Console cable (rollover):

- PC to Router console port (for initial router configuration)

* cross-over cable:

- PC to PC

- Router Ethernet to Router Ethernet

- Switch to switch

- Hub to hub

* Straight-through cable:

- PC to switch

- PC to hub

- Router to switch

- Router to hub

* Making WAN Connections

The cable is used as a V.35 connection to a Physical layer device such as a

CSU/DSU.

* Router Ethernet Interfaces:

Router Ethernet interfaces are used as the gateways for the end devices on the LANs

directly connected to the router.

Each Ethernet interface must have an IP address and subnet mask to route IP packets

In the example shown below (I know the IP addresses does not match, but concept is the

same), the IP address that is configured for the router Ethernet interface is going to be the

default gateway IP address for the PC inside your subnet. Also, the other way of saying it

is, the default gateway address configured on your PC is the router’s ethernet IP address.

Also, the IP address for the router and IP address for the PC, they must be in the same

subnet.

To configure an Ethernet interface follow these steps:

– Router#config t

– Router(config)#interface FastEthernet 0/0

– Router(config-if)#ip address ip_address netmask

– Router(config-if)#no shutdown

** Pay attention on the prompt needed and the command needed

Serial interfaces require a clock signal to control the timing of the communications.

– In most environments, a DCE device such as a CSU/DSU will provide the clock.

– By default, Cisco routers are DTE devices, but they can be configured as DCE

devices.

– On serial links that are directly interconnected, as in our lab environment, one

side must operate as DCE to provide a clocking signal:

• Router(config)#interface Serial 0/0/0

• Router(config-if)#ip address ip_address netmask

• Router(config-if)#clock rate 56000

• Router(config-if)#no shutdown

To configure console or virtual terminal line (telnet).

– Switch(config)#line console 0

– Switch(config-line)#password password

– Switch(config-line)#login

– Switch(config)#line vty 0 4 5 telnet session is setup with the password access.

– Switch(config-line)#password password

– Switch(config-line)#login

* Passwords are the primary defense against unauthorized access to network devices.The

passwords here are:

Console password - limits access using the console connection

Enable password - limits access to the privileged EXEC mode

Enable secret password - encrypted, limits access to the privileged EXEC mode

VTY password - limits device access using Telnet

* A Cisco network device contains two configuration files:

The running configuration file - used during the current operation of the device

– Stored in RAM, it is used to operate the device.

– Changes to the running configuration

The startup configuration file - used as the backup configuration and is loaded when the

device is started

– The startup configuration file is used during system startup to configure the

device.

– The startup configuration file is stored in NVRAM.

* Save the Changed Configuration

– Because the running configuration is stored in RAM, it is temporarily active while

the Cisco device is powered on.

– Saving the running configuration to the startup configuration in NVRAM

preserves the changes as the new startup configuration.

– Switch#copy running-config startup-config

* Removing All Configurations

If undesired changes are saved to the startup configuration, this requires erasing the

startup configuration and restarting the device.

Router#erase startup-config.

The startup configuration file is stored in NVRAM will be erased

Reload the device to remove the current running configuration file