The OSI Reference Model

Using the OSI model to discuss networking concepts has the following advantages:

Answer:

• Provides a common language

or reference point between network professionals

• Divides networking tasks

into logical layers for easier comprehension

• Allows specialization of

features at different levels

• Aids in troubleshooting
• Promotes standards of interoperability

between networks and devices

• Provides modularity in

networking features (developers can change features without changing the entire approach)

Functions Performed at Each OSI Model Layer

The following table compares the functions performed at each OSI model layer:

Answer:

Application (Layer 7)

The Application layer integrates network functionality into the host operating system, and enables network services.

• Protocols: HTTP, Telnet ,

FTP, TFTP, SNMP, DNS, DHCP, SMTP

• PDU: Data
• Devices: Computers / User

Interface

Presentation (Layer 6)

The Presentation layer formats or “presents” data into a compatible form. Presentation layer ensures:

• Formatting and translation

of data between systems.

• Negotiation of data transfer

syntax between systems, through converting character sets to the correct format.

• Encapsulation of data into

message envelopes by encryption and compression.

• Restoration of data by

decryption and decompression.

• Protocols: SSL, TLS, JPEG,

TIFF

• PDU: Data

Session (Layer 5)

The Session layer’s primary function is managing the sessions in which data is transferred. Functions at this layer include:

• Management of multiple

sessions (each client connection is called a session). A server can concurrently maintain thousands of sessions.

• Assignment of the session

ID number to each session to keep data streams separate.

• Set up, maintain, and tear

down communication sessions.

• Protocols: TCP
• PDU: Data

Transport (Layer 4)

Transport layer functions include:

• End-to-end flow control.
• Port and socket numbers.
• Segmentation, sequencing,

and combination.

• Connection services,

either reliable (connection-oriented) or unreliable (connectionless) delivery of data.

• Protocols: TCP, UDP
• PDU: segment (MTU

1500 bytes)

Network (Layer 3) The Network layer describes how data is routed across networks and on to the destination. Network layer functions include:

• Identifying hosts and

networks using logical addresses.

• Maintaining a list of

known networks and neighboring routers.

• Determining the next

network point to which data should be sent. Routers use a routing protocol to take into account various factors such as the number of hops in the path, link speed, and link reliability to select the optimal path for data.

• Protocols: RIP, RIPV2,

IGRP, EGP, IGP, EIGRP, OSPF, OSPFV3

• PDU: Packet

Devices: routers, layer 3 switches, firewalls, brouters

Data Link (Layer 2) – Logical Link Control – Media Access Control (MAC) The Data Link layer defines the rules and procedures for hosts as they access the Physical layer. These rules and procedures specify or define:

• How hosts on the network

are identified (physical or MAC address).

• How and when devices can

transmit on the network medium (media access control and logical topology).

• How to verify that the

data received from the Physical layer is error free (parity and CRC).

• How devices control the

rate of data transmissions between hosts (flow control).

• Protocols: PPP, SLIP,

L2TP, CDP

• PDU: Frame

Devices: switches, nics, multilayer switch, bridges, WAPs

Physical (Layer 1) The Physical layer of the OSI model sets standards for sending and receiving electrical signals between devices. Protocols at the Physical layer identify:

• How digital data (bits)

are converted to electric pulses, radio waves, or pulses of lights.

• Specifications for cables

and connectors.

• The physical topology.
• Protocols: SONET, DSL, T1,

Ethernet

• PDU: Bits

Devices: hubs, repeaters, nics, modems, cables, cable connectors, media converters

The Three-Way Handshake

To establish a connection, TCP uses a three-way handshake. Before a client attempts to connect with a server, the server must first bind to and listen at a port to open it up for connections: To establish a connection, the three-way (or 3-step) handshake occurs:

Answer:

• SYN: The active open is

performed by the client sending a SYN to the server

• SYN-ACK: In response, the

server replies with a SYN-ACK. Includes rules/parameters between hosts

• ACK: Finally, the client

sends an ACK back to the server. Notify client that connection agreement has been accepted

Flow Control and Windowing

Flow Control: TCP users an end-to-end flow control protocol to avoid having the sender send data too fast for the TCP receiver to receive and process it reliably. For example, if a PC sends data to a Smartphone that is slowly processing received data, the Smartphones must regulate the data flow so as not to be overwhelmed. Sliding Window: uses a sliding window flow control protocol. In each TCP segment, the receiver specifies…

Answer:

…the amount of received data (in bytes) that it is willing to buffer for the connection. The sending host can send only up to that amount of data before it must wait for an acknowledgment and window update from the receiving host.

Advantages and Disadvantages of Repeaters and Hubs

Advantages of Repeaters and Hubs:

• Repeaters and hubs can

extend a network total distance

• Repeaters and hubs do not

seriously affect network performance

• Certain repeaters can

connect networks using different physical media. Disadvantages of Repeaters and Hubs:

Answer:

• Repeaters and hubs cannot

connect different network architectures, such as Token Ring and Ethernet.

• Repeaters and hubs do not

reduce network traffic

• Repeaters and hubs do not

segment the network

Advantages and Disadvantages of Bridges

Advantages of Bridges:

• Bridges can extend a

network by acting as a repeater

• Bridges can reduce network

traffic on a segment by subdividing network communications

• Bridges increase the

available bandwidth to individual nodes because fewer nodes share a collision domain

• Bridges reduce collisions
• Some bridges connect

networks using different media types and architectures. Disadvantages of Bridges:

Answer:

• Because bridges do more

than repeaters by viewing MAC addresses, the extra processing makes them slower than repeaters - and hubs. Bridges forward broadcast frames indiscriminately, so they do not filter broadcast traffic

• Bridges are more expensive

than repeaters and hubs.

Advantages and Disadvantages of Switches

Advantages of Switches:

• Switches increase

available network bandwidth

• Switches reduce the

workload on individual computers

• Switches increase network

performance

• Networks that include

switches experience fewer frame collisions because switches create collision domains for each connection (a process called micro segmentation)

• Switches connect directly

to workstations. Disadvantages of Switches:

Answer:

• Switches are significantly

more expensive than bridges

• Network connectivity

problems can be difficult to trace through a switch

• Broadcast traffic may be

troublesome.

Advantages and Disadvantages of Routers

Advantages of Routers:

• Routers can connect

different network architectures, such as Ethernet and Token Ring

• Router can choose the best

path across an internetwork using dynamic routing techniques

• Routers reduce network

traffic by creating collision domains

• Routers reduce network

traffic by creating broadcast domains Disadvantages of Routers:

Answer:

• Routers are more expensive

than other devices

• Dynamic router

communications (inter-router communication) cause additional network overhead, which results in less bandwidth for user data.

• Routers are slower than

other devices because they must analyze a data transmission from the Physical through the Network layer, whereas bridges and switches only read two layers of information: the Physical and Data Link

Collision and Broadcast Domains

Collision Domains: Only one device in the collision domain may transmit at any one time, and the other devices in the domain listen to the network in order to avoid data collisions. Each connection from a single PC to a Layer 2 switch is ONE Collision domain. For example, if 5 PCs are connected with separate cables to a switch, we have 5 Collision domains. If this switch is connected to another switch or a router, we have one collision domain more. If 5 Devices are connected to a Hub, this is ONE Collision Domain. Each device that is connected to a Layer 1 device (repeater, hub) will reside in ONE single collision domain. (shared bandwidth). Broadcast Domains: Broadcasting sends a message to everyone on the local network (subnet). No matter how many hosts or devices are connected together, if…

Answer:

…they are connected with a repeater, hub, switch or bridge, all these devices are in ONE Broadcast domain. A Router is used to separate Broadcast-Domains. So, if a router stands between all these devices, we have TWO broadcast domains. An example for Broadcasting would be a DHCP Request from a Client PC. The Client is asking for a IP Address, but the client does not know how to reach the DHCP Server. So the client sends a DHCP Discover packet to EVERY PC in the local subnet (Broadcast). But only the DHCP Server will answer the Request.

CSMA-CD and CSMA-CA

CSMA-CD: (Carrier Sense Multi-Access with Collision Detection) is a media access method in which an host detects if a signal is being transmitted. If no signal is detected on the wire, then the host will transmit. There does exist the possibility that two or more hosts may sense the absence of a signal and transmit at the same time. If this happens, there is a collision. CSMA-CA: (Carrier Sense Multi-Access with Collision Avoidance) stands for…

Answer:

…Collision Sense Multiple Access with Collision Avoidance. This is used for wireless media access control. It uses a send and reply like the TCP three way hand shake, RTS – request to send, and CTS – Clear to send) After each message is sent the hosts associated to the wireless access point run a randomization algorithm which sets a random priority on who gets to send next. That along with many control fields help to mitigate some of the interferences and other radio related wireless problems.

Half-Duplex vs. Full-Duplex

How does half duplex differ from full-duplex communications?

Answer:

• Half-duplex communications

need that each participant only transmits when the other is listening

• By using full-duplex

communications, both parties can transmit simultaneously

• The benefit of full-duplex

mode is less delay in transmitting a message, because a computer could receive and transmit information simultaneously

Ethernet Addressing (Mac Address)

What is Ethernet Addressing?

Answer:

• Reference as Media Access

Control

• Size: 48 bit hex-decimal

address (6 byte)

• First set of 24 bits is

considered to be the OUI (organization unique identifier)

• Second set of 24 bits is

considered to be the MAC (unique per vendor) You should also know the following facts about Ethernet: The maximum cable length for UTP Ethernet “T” implementations are 100 meters for all standards. Ethernet standards support a maximum of 1024 hosts on a single subnet. 10GBase standards ending in W (i.e. 10GBaseSW) are used for SONET implementations. You may also see 10Base2 and 10Base5 Ethernet implementations, both of which are older implementations using coaxial cable. You will not be required to know these for the CCNA exam.

How to Convert Binary Numbers to Decimal Numbers

The most popular, and easiest way to convert a binary number to decimal is using a table like so:

Answer:

MAGIC CHART – DECIMAL CHART 128

64

32

16

8

4

2

1

0

0

1

1

1

0

0

1

0 + 0 + 32 + 16 + 8 + 0 + 0 + 1

57 To convert a binary number to a decimal number

• Determine the decimal

value for each of the bits

• Add up the bit values
• 00111001 =57
• 57 = 00111001

Checking results = you can use addition or subtraction, if you use addition please only add values that have a 1 value, if you are using subtraction – take the total value of the chart and subtract anywhere that have 0’s Bit = 0 or 1 Nibble = 4 bits = 0101, 0000, 1111 Byte = 8 bits = 1 octet = 11111111, 00000000, 10101010

Baseband vs. Broadband

The baseband transmission model differs from broadband communications in the following ways:

Answer:

• The baseband transmission

method uses the media in such a way that the entire capacity of the cable is taken up by a single transmission

• In broadband

communications the communicators use different frequencies to separate their messages from others by using the same media at the same time

Ethernet Specifications

Ethernet standards are defined by the work of the IEEE 802.3 committee. The following table compares the characteristics of various Ethernet implementations.

Answer:

Coaxial Cable Facts

Coaxial cable has the following advantages and disadvantages: Advantages

• Highly resistant to EMI

(electromagnetic interference)

• Highly resistant to

physical damage

Disadvantages

• Expensive
• Inflexible construction

(difficult to install)

• Unsupported by newer

networking standards The table below describes the different coaxial cable grades:

Answer:

Grade Uses Resistance Rating RG-58 10Base2 Ethernet networking (also called Thinnet) 50 ohms RG-59 Cable TV and cable networking 75 ohms RG-6 Cable TV, satellite TV, and cable networking RG-6 has less signal loss than RG-59, and is a better choice for networking applications, especially where longer distances (over a few feet) are involved. 75 ohms RG-8 10Base5 Ethernet networking (also called Thicknet) 50 ohms The table below describes the types of connectors used with coaxial cable.

Twisted Pair Facts

Twisted pair cables support a wide variety of fast, modern network standards. Twisted pair cabling is composed of the following components:

• PVC or plenum plastic

insulation surrounds each wire. Plenum cable is fire resistant and non-toxic. It must be used when wiring above ceiling tiles. PVC cable cannot be used to wire above ceilings because it is toxic when burned.

• Twisted pair cable can be

classified according to the makeup of the outer sheath:

• Shielded Twisted Pair

(STP) has a grounded outer copper shield around the bundle of twisted pairs or around each pair. This provides added protection against EMI.

• Unshielded Twisted Pair

(UTP) does not have a grounded outer copper shield. UTP cables are easier to work with and are less expensive than shielded cables. The table below describes the different unshielded twisted pair (UTP) cable types (categories):

Answer:

Type Connector Description Phone cable RJ-11 Used to connect a PC to a phone jack in a wall outlet to establish a dial-up Internet connection. Has two pairs of twisted cable (a total of 4 wires). Cat 3 RJ-45 Designed for use with 10 megabit Ethernet or 16 megabit token ring. Cat 5 RJ-45 Supports 100 megabit Ethernet and ATM networking. Cat 5 specifications also support gigabit (1000 Mb) Ethernet. Cat 5e RJ-45 Similar to Cat 5 but provides better EMI protection. Supports 100 megabit and gigabit Ethernet. Cat 6 RJ-45 Supports 10 gigabit Ethernet and high-bandwidth, broadband communications. Cat 6 cables often include a solid plastic core that keeps the twisted pairs separated and prevents the cable from being bent too tightly. Additional standards for Cat 6 include Cat 6a (advanced) and Cat 6e (enhanced) which provide better protection against EMI. Each type of UTP cable can be substituted for any category below it, but never for a category above. For example, Cat 6 can be substituted for a task requiring Cat 5e; however, neither Cat 5 nor Cat 3 should be used for this particular task. The table below describes the two types of connectors used with twisted pair cables.

Fiber Optic Facts

Fiber Optic Facts:

To connect computers using fiber optic cables, you need two fiber strands. One strand transmits signals, and the other strand receives signals. Fiber optic cabling is composed of the following components:

• The core carries the

signal. It is made of plastic or glass.

• The cladding maintains the

signal in the center of the core as the cable bends.

• The sheathing protects the

cladding and the core. Fiber optic cabling offers the following advantages and disadvantages:

Answer:

Advantages

• Totally immune to EMI

(electromagnetic interference)

• Highly resistant to

eavesdropping

• Supports extremely high

data transmission rates

• Allows greater cable distances

without a repeater

Disadvantages

• Very expensive
• Difficult to work with
• Special training required

to attach connectors to cables Multi-mode and single mode fiber cables are distinct from each other and not interchangeable. The table below describes multi-mode and single mode fiber cables. Type Description Single Mode

• Transfers data through the

core using a single light ray (the ray is also called a mode)

• The core diameter is

around 10 microns

• Supports a large amount of

data

• Cable lengths can extend a

great distance (up to 62 miles)

Multi-mode

• Transfers data through the

core using multiple light rays

• The core diameter is

around 50 to 100 microns

• Cable lengths are limited

in distance (14,000 – 18,000 feet)

Fiber Optic Cabling Connector Types

Fiber optic cabling uses the following connector types:

Answer:

Straight-Through, Crossover and Rolled Cables

For each of the following situations, determine whether a straight-through, crossover, or rolled cable would be used:

Answer:

Description Cable Type ·
Host to Host

Crossover ·
Host to switch or hub

Straight-through ·
Router direct to host

Crossover ·
Switch to switch

Crossover ·
Router to switch or hub

Straight-through ·
Hub to hub

Crossover ·
Hub to switch

Crossover · Host to a router console serial communication (COM) port

Rolled

Data Encapsulation Steps

What are the eight steps involved with data encapsulation?

Answer:

Step 1 The user data is sent from an application to the application layer. Step 2 The application layer adds the application layer header (Layer 7 header) to the user data. The Layer 7 header and the original user data become the data that is passed down to the presentation layer. Step 3 The presentation layer adds the presentation layer header (Layer 6 header) to the data. This then becomes the data that is passed down to the session layer. Step 4 The session layer adds the session layer header (Layer 5 header) to the data. This then becomes the data that is passed down to the transport layer. Step 5 The transport layer adds the transport layer header (Layer 4 header) to the data. This then becomes the data that is passed down to the network layer. Step 6 The network layer adds the network layer header (Layer 3 header) to the data. This then becomes the data that is passed down to the data link layer. Step 7 The data link layer adds the data link layer header and trailer (Layer 2 header and trailer) to the data. A Layer 2 trailer is usually the frame check sequence (FCS), which is used by the receiver to detect whether the data is in error. This then becomes the data that is passed down to the physical layer. Step 8 The physical layer then transmits the bits onto the network media.

Cisco Three-Layer Hierarchical Model

Cisco Three-Layer Hierarchical Model:

The Core Layer: The core layer provides an optimized and reliable transport structure by forwarding traffic at very high speeds. Devices at the core layer should not be burdened with any processes that stand in the way of switching packets at top speed. This includes the following:

• Access-list checking
• Data encryption
• Address translation

The Distribution Layer: The distribution layer is located between the access and core layers. The purpose of this layer is to provide boundary definition using access lists and other filters to limit what gets into the core. Therefore, this layer defines policy for the network. A policy is an approach to handling certain kinds of traffic, including the following:

• Routing updates
• Route summaries
• VLAN traffic

Use these policies to secure networks and to preserve resources by preventing unnecessary traffic. The Access Layer: The access layer…

Answer:

…supplies traffic to the network and performs network entry control. End users access network resources by way of the access layer. Acting as the front door to a network, the access layer employs access lists designed to prevent unauthorized users from gaining entry.

The TCP/IP & DoD Model

The following table below illustrates the TCP/IP and D0D Model:

Answer:

Process/Application Application Presentation Session

Internet Network Network Access Data Link Physical

All About the Application Layer Protocols

The table below illustrates the Application Layer Protocols:

Answer:

Host-to-Host Layer and Internet Layer Protocols

Host-to-Host Layer and Internet Layer Protocols:

Host-To-Host Protocols: Transport Control Protocol (TCP) Allows users to access resources on another machine. All data is seen in clear text (not recommended for use) User Datagram Protocol (UDP) Similar to Telnet but it sets up a secure session (recommended over telnet). All data is encrypted during the session

TCP UDP Sequenced Unsequenced Reliable Unreliable Connection-oriented Connectionless (best effort delivery) Builds virtual circuit Low overhead ACK (acknowledgements) NACK (no acknowledgements) Windowing, flow control No windowing, no flow control

Port Numbers TCP UDP Telnet – 23 SNMP – 161 SMTP – 25 TFTP – 69 HTTP – 80 DNS – 53 FTP – 20, 21 DHCP – 67 DNS – 53 NTP – 123 HTTPS – 443

SSH – 22

POP3 – 110

IMAP 4 – 143

Internet Layer Protocols:

Answer:

• Internet Protocol (IP) –

analyze each packet to decide where the packet is sent

• Internet Control Message

Protocol (ICMP) – Use to gives status updates about a host or network

• Address Resolution

Protocol (ARP) – resolves IP addresses to MAC addresses

IP Addressing and IPV4 Address Type

Network Classes Ranges Class A 0-127 Class B 128-191 Class C 192-223 Class D – Multicast Addresses 224-239 Class E – Experiment Addresses 240-255 Loopback Address – Reserve for testing 127.0.0.1 Private IP Addressing Network Classes Ranges Class A 10.0.0.0 – 10.255.255.255 Class B 172.16.0.0 – 172.31.255.2555 Class C 192.168.0.0 – 192.168.255.255 IPV4 Address Types

Answer:

Classifications Loopback Use to test IP stack on local computer Layer 2 broadcast Sent to all hosts on the LAN Broadcasts Sent to all hosts on the Network Unicast Sent to one host Multicast Sent to many host on different networks (group)

Subnetting Basics

Rules to follow for Subnetting:

1. What is my default subnet

mask 2. How many networks can I have 3. How many hosts can I have 4. What is my network address 5. What is my valid range 6. What is my broadcast address Formula: 2x = the number of networks x = the number of 1’s 2y – 2 = the number of hosts y= the number of 0’s RESERVED = NETWORK /BROADCAST

192.168.100.37/25 Class C Example below:

Answer:

a. 11111111.11111111.10000000 255. 255. 255. 128 b. 21 = 2 network c. 27 = 128 – 2 = 126 host d. Block size – 256 – (subnet mask) 256-128 = 128 Network =
192.168.100.0 192.168.100.128 Fhost
192.168.100.1
192.168.100.129 Lhost
192.168.100.126
192.168.100.254 Bcast
192.168.100.127
192.168.100.255

Address range: 192 – 223 Number of network bits: 24 Number of networks: 2,097,152 Number of host bits: 8 Number of hosts per network: 28 = 256 Number of Useable Hosts per network: 28 – 2 = 254 Default Subnet Mask: 255.255.255.0 or /24

Example Address Class: C IP Address: 192.102.22.82 / 24 Subnet Mask: 255.255.255.0 Network Address is: 192.102.22.0 Broadcast Address is: 192.102.22.255 Number of Useable host addresses: 192.102.22.1 – 192.102.22.254 172.16.0.0/17 – Class B Example a. 11111111.11111111.10000000.00000000 255.
255. 128
0 b. 21 = 2 network c. 215 = 32,768 -2 = 32,766 d. Block size – 256 – (subnet mask) 256-128 = 128 Network = 172.16.0.0 | 172.16.128.0 Fhost 172.16.0.1 | 172.16.0.1 Lhost 172.16.127.254 | 172.16.255.254 Bcast 172.16.127.255 | 172.16.255.255

Class B Address range: 128 – 191

• Number of network bits: 16
• Number of networks: 16,384
• Number of host bits: 16
• Number of hosts per

network: 216 = 65,536

• Number of Useable Hosts

per network: 216 – 2 = 65,534

• Default Subnet Mask:

255.255.0.0 or /16

Address Class: B IP Address: 130.61.22.204 / 16 Subnet Mask: 255.255.0.0 Network Address is: 130.61.0.0 Broadcast Address is: 130.61.255.255 Number of Useable host addresses: 130.61.0.1 – 130.61.255.254 172.16.0.0/16 – Class A Example 11111111.11111111.0000000.00000000 255. 255. 0 0 28 = 256 network = 65,536 -2 = 65,534 Block size – 256 – (subnet mask) 256-255 = 1 Network =
10.0.0.0

  10.1.0.0

Fhost
10.0.0.1
10.1.0.1 Lhost
10.0.255.254
10.1.255.254 Bcast
10.0.255.255
10.1.255.255

Address Class: A IP Address: 64.133.65.101 / 8 Network Address is: 64.0.0.0 Broadcast Address is: 64.255.255.255 Subnet Mask: 255.0.0.0 Number of Useable host addresses: 64.0.0.1 – 64.255.255.254

The Magic Chart – Decimal Chart

128 64 32 16 8 4 2 1 =255

Checking results = you can use addition or subtraction, if you use addition please only add values that have a 1 value, if you are using subtraction – take the total value of the chart and subtract anywhere that have 0’s IP Address: 192.168.50.109 Bit = 0 or 1 Nibble = 4 bits = 0101, 0000, 1111 Byte = 8 bits = 1 octet = 11111111, 00000000, 10101010

Class CCIDR Notation Default subnet Mask / Binary Number of Networks Number of host / valid range /24 00000000 = 0 1 256 host / 254 /25 10000000 = 128 2 128 host / 126 /26 11000000 = 192 4 64 host /
62 /27 11100000 = 224 8 32 host /
30 /28 11110000 = 240 16 16 host /
14 /29 11111000 = 248 32 8 host /
6 /30 11111100 = 252 64 4 host /
2 /31 11111110 = 254 128 2 host/
1 /32 11111111 = 255 0 0

The chart below displays the power of 2’s:

Answer:

Variable Length Subnet Masking (VLSM)

VLSM enables a network number to be configured with different subnet masks on different interfaces.

• Conserves IP addresses.
• More efficient use of available

address space.

• Allows for more

hierarchical levels within an addressing plan.

Steps for VLSM:

• List the number of hosts

required per network beginning with the largest to the smallest.

• Convert the subnet mask to

binary.

• Draw a line where the

network portion ends.

• Ask yourself the question…

How many bits do I need to support the required number of hosts?

• Move the line to show your

new network portion.

• Determine your new magic

number.

• Finish subnetting using

the new magic number. The starting address is always the first network. You cannot go past the next network of the previous level.The following pictures illustrate the VLSM process:

Answer:

How to Perform Route Summarization

To Summarizing networks IP address or route into a single address and mask can be done in three steps. Let’s use the following four networks below as an example:

Answer:

Example 17016.0.0/16 170.17.0.0/16 170.18.0.0/16 170.19.0.0/16 Step 1: List the networks in binary format: 170.16.0.0/16 = 10101010.00010000 00000000 00000000 170.17.0.0/16 = 10101010.00010001.00000000.00000000 170.18.0.0/16 = 10101010.00010010.00000000.00000000 170.19.0.0/16 = 10101010.00010011.00000000.00000000 Step 2: Count from the left, the number of most matching bits to determine the subnet mask for the summary route or IP address. 170.16.0.0/16 = 10101010.00010000 00000000 00000000 170.17.0.0/16 = 10101010.00010001.00000000.00000000 170.18.0.0/16 = 10101010.00010010.00000000.00000000 170.19.0.0/16 = 10101010.00010011.00000000.00000000 You can see from the example that there are 12 left-most matching bits match. This is the prefix (CIDR), or subnet mask, for the summarized route or IP address: /12 or 255.240.0.0.

Modes and Router Configurations

MODES:

Router Configurations:

Answer:

Router#configure terminal Router(config)# Router(config)#hostname R1 ß-configure Passwords R1(config)#enable password cisco R1(config)#enable secret ciscoexam

R1(config)#line vty 0 4 R1(config-line)#password remote ß-configure Telnet R1(config-line)#login

R1(config)#line console 0 R1(config-line)#password rollover ß- configure Console R1(config-line)#login

R1(config)#banner motd ~
ß- configure banner Enter TEXT message. End with the character ‘~’. @@@@@@@@@@@@@@@@@@@@@@@@@@@@@ WARNINGS DO NOT ATTEMPT TO CONNECT!!! @@@@@@@@@@@@@@@@@@@@@@@@@@@@@ ~ R1(config)#

	ß- configure ip addresses and descriptions

interface fa0/0 R1(config-if)#ip address 192.168.10.65 255.255.255.240 R1(config-if)#description connection to LAN1 R1(config-if)#no shut …. R1(config-if)#exit R1(config)#interface fa0/1 R1(config-if)#ip address 192.168.20.129 255.255.255.248 R1(config-if)#description connection to LAN2 R1(config-if)#no shut

R1(config-if)#exit R1(config)#interface eth0/1/0 R1(config-if)#ip address 174.25.98.102 255.255.255.252 R1(config-if)#description connection to R2 R1(config-if)#no shut

R1#copy run start

               ß saves configs from RAM to NVRAM

Components of Cisco Router and Switch

Random Access Memory (RAM):

• Stores routing

tables- Holds ARP cache

• Holds fast-switching cache
• Performs packet buffering

as shared RAM

• Maintains packet-hold

queues

• Provides temporary memory

for the configuration file of a router while the router is powered on

• Loses content when a

router is powered down or restarted Nonvolatile Random AccessMemory (NVRAM):

• Provides storage for the

startup configuration file• •Retains content when a router is powered down or restarted Flash Memory (Flash):

• Holds the IOS image
• Allows software to be

updated without removing and replacing chips on the processor- Retains content when a router is powered down or restarted- Can store multiple versions of IOS software

• Is a type of electrically

erasable programmable read-only memory (EEPROM) Read Only Memory (ROM):

• Maintains instructions for

power…

Answer:

…on self test (POST) diagnostics

• Stores the bootstrap

program and the basic operating system software

• Requires replacing

pluggable chips on the motherboard for software upgrades

Checking Network Connectivity and Troubleshooting

Ping: Determines whether IP connectivity exist Trace Route: Trace route displays the…

Answer:

…path the packet takes to reach its destination.

Static Routing, Dynamic Routing and Default Routing

• Routers can be configured

to route traffic based on static routes that have to be manually entered by an administrator Static routing is a good choice for networks that: never change, are small in size or have only one router, or have only one way out of the network. Topology change requires manual update

• Default Routes

R1(config)#ip route 0.0.0.0 0.0.0.0 R1(config)#ip route 0.0.0.0 0.0.0.0

• Dynamic routes that are

created dynamically by a routing protocol:

Answer:

• Dynamic routing is a good

choice if a network has multiple routers, is part of a larger network, or if the network changes frequently

• Relies on routing protocol

to determine how to communicate with neighboring routers and maintains those networks in routing tables.

Routed and Routing Protocols

• A routed protocol is a

protocol that is routable over multiple networks like the internet. TCP/IP

• A routing protocol is a

protocol used by routers to share information with each other Routing protocols describe the following: How updates are sent, what knowledge is sent, when to send the knowledge, RIP, EIGRP, OSPF, and ISIS. The tables below provide an illustration of the routed and routing protocols:

Answer:

RIPv1 Characteristics

• Classful routing– RIP is a

classful routing protocol, it does not send or receive subnet masks, it assumes classful subnet masks

• Periodic updates– RIP

broadcasts routing updates every 30 seconds. It broadcasts the entire routing table in the update.

• Triggered updates– RIP

also broadcasts updates when there is a change in the topology, like a network going up or down.

• Metric– RIP’s metric is

hop count. RIP’s maximum distance is 15 hops. 16 hops is infinity and is used to mark a route as dead.

• Administrative Distance–

RIP’s administrative distance is 120. AD ranks the trustworthiness, or reliability of the route, the lower the administrative distance the better the route.

• Hold Down Timer– RIP uses

a hold down timer of 180 seconds so that it does not propagate bad routes and does not have a count-to-infinity routing loop. Route is flushed at 240 seconds.

• Load Balancing– Default

load balancing across 4 equal cost routes. Can go up to 6 routes. Remaining RIPv1 characteristics below:

Answer:

• Count to infinity– is

prevented by hold down timers and by RIPs maximum metric of 15 hops.

• Routing Loops– are

prevented by: Hold Down Timer, Split Horizon Rule, Route Poisoning, Route Poisoning with Poison Reverse, as well as TTL.

• Automatic Route Summarization.

RIP automatically summarizes routes into classful network ranges because it will not allow non-classful network configuration or the propagation of non-classful subnet masks. It can only advertise classful networks.

• Transport Layer– RIP sends

out updates on UDP port 520

OS CLI commands to use with RIP

• routerA(config)#router rip

activate RIP

routerA(config-router)#network add a participating network and interface

router(config-router)#passive-interface to stop RIP from sending updates out of an interface

• router#show running-config

to verify your configuration

• router#show ip route

to verify your routing table

• router#show ip protocols

to…

Answer:

…verify your RIP configuration router#copy running-config startup-config to save your configuration routerA(config)#router rip activate RIP routerA(config-router)#version 2 enables RIPv2 routerA(config-router)#network add a participating network and interface router(config-router)#passive-interface to stop RIP from sending updates out of an interface router#show running-config to verify your configuration router#show ip route to verify your routing table router#show ip protocols to verify your RIP configuration router#copy running-config startup-config to save your configuration

RIPv2 vs RIPv1

RIPv2 Differences from RIPv1

• VLSM and CIDR – is

supported by sending the subnet mask and the next hop address in its routing updates.

• Multicasts – its routing

updates to 224.0.0.9. instead of broadcasting to 255.255.255.255 like RIPv1

• Authentication – RIPv2

supports md5 authentication

• Updates – RIPv2 sends and

receives version 2 updates only. RIPv1 sends version 1 updates and receives both 1 and 2; however version 2 information is ignored. RIPv2 Similarities to RIPv1…

Answer:

• Auto Summarizes by default

(You will need to turn this off if you have discontiguous networks)

• Distance Vector Protocol
• Hop Count is the metric

with a maximum of 15 hops, 16 is infinity and is dropped.

EIGRP Characteristics

• VLSM & CIDR – EIGRP

has support for variable length subnet masks (VLSM) and classless inter domain routing (CIDR).

• DUAL algorithm – The

diffusing update algorithm or DUAL, provides guaranteed and optimized loop free routes.

• Successor & Feasible

Successor routes – The successor route is the best route to a destination network. If available, DUAL and the EIGRP topology database will also calculate a guaranteed loop free backup route called the Feasible Successor route.

• Partial & Bounded

Updates – for faster convergence times. No periodic updates like RIP. EIGRP only sends information when there is a change in the network, like a network link going down. EIGRP does not send the entire routing table, just the information that has changed and only to those routers that need the new information.

• Routing Metrics – EIGRP’s

routing metric is not…

Answer:

…based on hop count like RIP, it is based instead on: Bandwidth, Load, Delay and Reliability, with Bandwidth and then Delay being the most important factors. EIGRP also features MTU and Hop Count as metric vectors, though they are not used in route calculations.

EIGRP Multiple Tables

• Routing Table – the best

“loop free” network routes are placed in the routing table

• Neighbor Table – neighbor

adjacencies are maintained in this table

• Topology Table –

Answer:

• maintains “loop

free” backup routes known as successor routes and feasible successor routes

OS CLI Commands to Use with EIGRP

• router(config)# router

eigrp <AS/ID-number>

• router(config-router)#

network

• router(config-router)# no

auto-summary

• router(config-router)#

redistribute static

router(config-router)#passive-interface

• router(config-router)# exit
• router(config-router)# end

The following show commands are useful in verifying and troubleshooting EIGRP operation and configuration, as well as identifying the successor and feasible successor routes:

Answer:

• router# show ip eigrp

neighbor

• router# show ip eigrp

topology

• router# show running-config
• router# show ip protocols
• router# show ip route

OSPF Characteristics

• Algorithm – Dijsktra’s SPF

algorithm

• Metric – Cost, which is

based on the bandwidth of a link

• Administrative Distance –

110

• Process-ID number – the

process-id number is declared when OSPF is started/configured and is a number from 1 to 65535. The process id number does NOT need to match other OSPF routers in the area in order to create adjacencies

• Wildcard bits/mask – The

wildcard mask is the inverse of a network subnet mask (e.g. 255.255.255.0 is 0.0.0.255). It is declared after the network number in the network command (see commands below)

• Area number – The area

number is a number from 0-255, declared at the end of the network command after the wildcard bits. Routers in the same area will exchange routing information or Link State Updates or LSUs

• Hello Interval – Hello

packets are sent every…

Answer:

…10 seconds by default. In order for OSPF routers to establish neighbor adjacencies and exchange routing information successfully, the hello interval needs to match all OSPF routers in the OSPF area.

• Dead Interval – The dead

interval is 40 seconds by default. The dead interval should be 4 times the hello interval, and needs to match all OSPF routers in the area

• Multiple Tables – Routing

Table, Topology Table, and Neighbor Adjacency Table

• DR and BDR Elections – In

broadcast multi-access networks (Ethernet), routers in the OSPF area will elect a Designated Router (DR) and a Backup Designated Router (BDR). The DR will be the receiver and distributor of Link-State Packets to other routers in the OSPF area. The BDR will wait, and be ready to take over the duties of the DR in case it fails.

OS CLI Commands to Use with OSPF

router(config)# router ospf router(config-router)# network area router(config-router)# router-id router(config-router)# passive-interface router(config-router)# auto-cost reference-bandwidth router(config-router)# default-information originate router(config-router)# end Router(config-router)# exit The following show commands are useful in verifying and troubleshooting OSPF operation and configuration, as well as identifying the router-ids and the identities of the DR and BDR:

Answer:

router# show ip ospf neighbor router# show ip ospf interface router# clear ip ospf process router# show running-config router# show ip protocols router# show ip route

Access Lists Overview

Access Lists Overview

• Limit network traffic
• Provide traffic flow

control

• Provide basic level of

security

• Decide which types of traffic

to forward or block

• Control which areas a

client can access

• Screen hosts to permit or

deny them access

• Standard Access Lists

Overview

• Checks source address
• Permits or denies entire

protocol suite Create the ACL Standard ACL (1-99) – checks source IP address – checks who you are not where you are going Example: access-list 12 permit 192.168.50.0 0.0.0.25…

Answer:

• Apply the ACL

A standard ACL is applied inbound or outbound on the router interface that is closest to the destination of the traffic. Extended Access Lists Overview

• Checks source and

destination address

• Permits or denies specific

protocols and applications Source and destination TCP and UDP ports Protocol type (IP, ICMP, TCP, UDP, or protocol number) Create the ACL Extended ACL (100-199) – checks source and destination IP address – checks who you are and where you are going Example: access-list 103 permit tcp 192.168.50.0 0.0.0.255 any eq 80 Apply the ACL An extended ACL is applied inbound or outbound on the router interface that is closest to the source of the traffic.

OS CLI Commands to Use with Standard Access List

Standard access list command format: access-list <1-99> <deny | permit> Standard access list command format: access-list <1-99> <deny | permit> host Deny or permit a class c network: router(config)#access-list 1 deny 192.168.1.0 0.0.0.255 router(config)#access-list 1 permit 192.168.2.0 0.0.0.255 Deny or permit a host: router(config)#access-list 1 deny 192.168.1.100 0.0.0.0 router(config)#access-list 1 deny host 192.168.1.100 router(config)#access-list 1 permit 192.168.1.101 0.0.0.0 router(config)#access-list 1 permit host 192.168.1.101 Deny or permit all hosts: router(config)#access-list 1 deny any router(config)#access-list 1 permit any Apply the access list to a router interface outbound and inbound:

Answer:

router(config)#interface fastethernet 0/0 router(config-if)#ip access-group 1 out router(config)#interface fastethernet 0/1 router(config-if)#ip access-group 1 in Deny or permit all hosts: router(config)#access-list 1 deny any router(config)#access-list 1 permit any