Download ICND -1 Interconnecting Cisco Networking

ICND -1
Interconnecting Cisco
Networking Devices
Assembled By David Roberts
Knowing what you
DON’T know is more
important than what
you DO know. It takes
both to have expertise.
Course Content
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This course focuses on providing the skills
and knowledge necessary to install,
operate, and troubleshoot a small branch
office Enterprise network, including
configuring a switch, a router, and
connecting to a WAN and implementing
network security. A Student should be able
to complete configuration and
implementation of a small branch office
network under supervision.
Course Objectives
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Describe how networks function, identifying major components,
function of network components and the Open System
Interconnection (OSI) reference model.
Using the host-to-host packet delivery process, describe issues
related to increasing traffic on an Ethernet LAN and identify
switched LAN technology solutions to Ethernet networking issues.
Describes the reasons for extending the reach of a LAN and the
methods that can be used with a focus on RF wireless access.
Describes the reasons for connecting networks with routers and
how routed networks transmit data through networks using TCP /
IP.
Describe the function of Wide Area Networks (WANs), the major
devices of WANs, and configure PPP encapsulation, static and
dynamic routing, PAT and RIP routing.
Use the command-line interface to discover neighbors on the
network and managing the router¿s startup and configuration .
Course Outline
Module 1 - Building a Simple Network
 Module 2 - Ethernet Local Area Networks
 Module 3 - Wireless Local Area Networks
 Module 4 - Exploring the Functions of
Routing
 Module 5 - Wide Area Networks
 Module 6 - Network Environment
Management
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Module 1 - Building a Simple
Network
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Connect 3 PC’s together in a Class C, Class B & Class A using
IP addresses provided below. Test connectivity with ping.
Class C: PC1: 10.0.0.15 /24 (255.255.255.0)
PC2: 10.0.0.16 /24 (255.255.255.0)
PC3: 10.0.0.17 /24 (255.255.255.0)
Class B: PC1: 10.0.1.15 /16 (255.255.0.0)
PC2: 10.0.2.15 /16 (255.255.0.0)
PC3: 10.0.100.1 /16 (255.255.0.0)
Class A: PC1: 100.200.100.100 /8 (255.0.0.0)
PC2: 100.200.200.200 /8 (255.0.0.0)
PC3: 100.1.2.3 /8 (255.0.0.)
Module 1 - Building a Simple
Network – Part 2
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With the Class A IP’s still in place, change the
subnet to a class B. Use a subnet of /16.
(255.255.0.0)
What happens to the connectivity between the
machines? Why?
What change to the IP address of PC3 can be
made in order to restore connectivity between
all three PC’s?
Module 1 - Building a Simple
Network – Part 3
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Reset all PC’s to the Class C addressing scheme:
Class C:
PC1: 10.0.0.15 /24 (255.255.255.0)
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PC2: 10.0.0.16 /24 (255.255.255.0)
PC3: 10.0.0.17 /24 (255.255.255.0)
On PC1 bring up a command line and type in “ping –t 10.0.0.16”
On PC2 type in “ping –t 10.0.0.17”
On PC3 type in “ping –t 10.0.0.15”
Load up a packet sniffer of your choice on one of the PC’s and monitor the NIC.
Write down the MAC address for each PC that you see in the sniffer.
What port are the pings coming in & out from?
What protocol are the ping packets being sent over?
What is the actual alpha-numeric hex string that the ping packet uses as its data? This
can be found in the hex information window. You may have to stop the scanner to
isolate one packet.
Why cant the sniffer see all three PC’s?
Module 2 - Ethernet Local Area
Networks
Frames are the format of data packets on the wire. Note that a frame
viewed on the actual physical hardware would show start bits,
sometimes called the preamble, and the trailing Frame Check
Sequence. These are required by all physical hardware and is seen in
all four following frame types. They are not displayed by packet
sniffing software because these bits are removed by the Ethernet
adapter before being passed on to the network protocol stack
software.
Module 2 - Ethernet Local Area
Networks – Part 2
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Main procedure of transmission over ethernet:
Frame ready for transmission
Is medium idle? If not, wait until it becomes ready and wait the interframe
gap period (9.6 µs in 10 Mbit/s Ethernet).
Start transmitting
Does a collision occur? If so, go to collision detected procedure.
Reset retransmission counters and end frame transmission
Collision detected procedure - Continue transmission until minimum packet
time is reached (jam signal) to ensure that all receivers detect the collision
Increment retransmission counter
Is maximum number of transmission attempts reached? If so, abort
transmission.
Calculate and wait random backoff period based on number of collisions
Re-enter main procedure at stage 1
Module 2 - Ethernet Local Area
Networks – Part 3
Dual speed hubs
In the early days of Fast Ethernet, Ethernet switches were relatively
expensive devices. However, hubs suffered from the problem that if there
were any 10BASE-T devices connected then the whole system would have
to run at 10 Mbit. Therefore a compromise between a hub and a switch
appeared known as a dual speed hub. These devices consisted of an
internal two-port switch, dividing the 10BASE-T (10 Mbit) and 100BASE-T
(100 Mbit) segments. The device would typically consist of more than two
physical ports. When a network device becomes active on any of the
physical ports, the device attaches it to either the 10BASE-T segment or the
100BASE-T segment, as appropriate. This prevented the need for an all-ornothing migration from 10BASE-T to 100BASE-T networks. These devices
are often known as dual-speed hubs, since the traffic between devices
connected at the same speed is not switched.
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Module 2 - Ethernet Local Area
Networks – Part 4
More advanced networks
Simple switched Ethernet networks, while an improvement over hub based Ethernet, suffer from a number of
issues:
They suffer from single points of failure. If any link fails some devices will be unable to communicate with other
devices and if the link that fails is in a central location lots of users can be cut off from the resources they require.
It is possible to trick switches or hosts into sending data to your machine even if it's not intended for it, as
indicated above.
Large amounts of broadcast traffic whether malicious, accidental or simply a side effect of network size can flood
slower links and/or systems.
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It is possible for any host to flood the network with broadcast traffic forming a denial of service attack against any hosts that run
at the same or lower speed as the attacking device.
As the network grows normal broadcast traffic takes up an ever greater amount of bandwidth.
If switches are not multicast aware multicast traffic will end up treated like broadcast traffic due to being directed at a MAC with
no associated port.
If switches discover more MAC addresses than they can store (either through network size or through an attack) some addresses
must inevitably be dropped and traffic to those addresses will be treated the same way as traffic to unknown addresses, that is
essentially the same as broadcast traffic (this issue is known as failopen).
They suffer from bandwidth choke points where a lot of traffic is forced down a single link.
Some switches offer a variety of tools to combat these issues including:
Spanning-tree protocol to maintain the active links of the network as a tree while allowing physical loops for
redundancy.
Various port protection features, as it is far more likely an attacker will be on an end system port than on a
switch-switch link.
VLANs to keep different classes of users separate while using the same physical infrastructure.
fast routing at higher levels to route between those VLANs.
Link aggregation to add bandwidth to overloaded links and to provide some measure of redundancy, although the
links won't protect against switch failure because they connect the same pair of switches.
Module 2 - Ethernet Local Area
Networks – Part 5
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Duplex:
Terms originally referring to specific circuit designs for
serial communication, but now referring more to specific
rules for data flow. A simplex circuit allows only one-way
communication from a transmitter to a receiver. A halfduplex circuit allows two-way communication, but only in
one direction at a time; that is, the two parties to the
connection must take turns transmitting and receiving
data. A full-duplex circuit allows both parties to send and
receive data simultaneously.
Module 2 - Ethernet Local Area
Networks – Part 6
Your typical RJ-45
connector. You will
find this connector
most commonly
on Cat-5 & Cat-6
twisted pair. The
RJ-45 has 8 brass
leads, 4 pairs
twisted together
to produce
minimal distortion
& signal loss on
the line.
Crossover cables are used when
connecting two PC’s or switches
directly together. Most network
equipment manufactured within
the last two years has auto Xover negotiation built into the
device.
Module 2 Ethernet Local
Area Networks
– Part 7
Console Cables are used to
directly connect to management
interfaces (serial port) on
network equipment.
Module 2 - Ethernet Local Area
Networks – Part 8
Your basic RJ-45 tip crimp tool.
Example of unshielded
twisted pair (top) & shielded
twisted pair (bottom).
Module 2 - Ethernet Local Area
Networks – Part 8-LAB
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At this point take a sample of Cat-5 & tip it
for crossover functionality.
Test the cable, why do the testers show
an error? Is the cable good or bad?
Use the crossover to bypass the switch
between two of the PC’s.
Module 3 - Wireless Local
Area Networks
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Wireless Encryption Types: WEP
Short for Wired Equivalent Privacy, a security protocol for wireless local area
networks (WLANs) defined in the 802.11b standard. WEP is designed to
provide the same level of security as that of a wired LAN. LANs are inherently
more secure than WLANs because LANs are somewhat protected by the
physicalities of their structure, having some or all part of the network inside a
building that can be protected from unauthorized access. WLANs, which are
over radio waves, do not have the same physical structure and therefore are
more vulnerable to tampering. WEP aims to provide security by encrypting data
over radio waves so that it is protected as it is transmitted from one end point to
another. However, it has been found that WEP is not as secure as once
believed. WEP is used at the two lowest layers of the OSI model - the data link
and physical layers; it therefore does not offer end-to-end security.
WEP is total crap & should NEVER be used on ANY wireless network unless it
is the ONLY encryption available.
Module 3 - Wireless Local
Area Networks – Part 2
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Wireless Encryption Types: WPA1
Short for Wi-Fi Protected Access, a Wi-Fi standard that was designed to improve
upon the security features of WEP. The technology is designed to work with
existing Wi-Fi products that have been enabled with WEP (i.e., as a software
upgrade to existing hardware), but the technology includes two improvements over
WEP:
Improved data encryption through the temporal key integrity protocol (TKIP). TKIP
scrambles the keys using a hashing algorithm and, by adding an integrity-checking
feature, ensures that the keys haven’t been tampered with.
User authentication, which is generally missing in WEP, through the extensible
authentication protocol (EAP). WEP regulates access to a wireless network based
on a computer’s hardware-specific MAC address, which isrelatively simple to be
sniffed out and stolen. EAP is built on a more secure public-key encryption system
to ensure that only authorized network users can access the network.
It should be noted that WPA is an interim standard that will be replaced with the
IEEE’s 802.11i standard upon its completion. (this was completed in 2004)
While WPA1 is very strong it can be broken with enough computing power, time &
a stupid administrator who doesn’t know how to pick & choose appropriate
passwords.
Using a password that includes at least one capitol, one number, one special char
(~ . $ ^ #) and that is a minimum of 25 characters ensures a secure wireless
network if one must use WPA1 for user compatibility.
Module 3 - Wireless Local
Area Networks – Part 3
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Wireless Encryption Types: WPA2
WPA2 implements the mandatory elements of 802.11i. In particular, in
addition to TKIP and the Michael algorithm, it introduces a new AESbased algorithm, CCMP, that is considered fully secure. Note that from
March 13, 2006, WPA2 certification is mandatory for all new devices
wishing to be Wi-Fi certified.
Vendor support:
Official support for WPA2 in Microsoft Windows XP was rolled out on 1
May 2005. Driver upgrades for network cards may be required.
Apple Computer supports WPA2 on all AirPort Extreme-enabled
Macintoshes, the AirPort Extreme Base Station, and the AirPort Express.
Firmware upgrades needed are included in AirPort 4.2, released July 14,
2005.
wpa_supplicant for Linux, BSD, and Windows supports WPA2 if used with
a supported wireless card/driver.
WPA2 is the only wireless encryption that has not been broken. It is the
strongest form of wireless security to date.
Module 3 - Wireless Local
Area Networks – Part 4
 Wireless Standards: IEEE 802.11 (B)
 Data Rate: Up to 11Mbps in the 2.4GHz band
 Products that adhere to this standard are
considered "Wi-Fi Certified." Not interoperable
with 802.11a. Requires fewer access points
than 802.11a for coverage of large areas.
Offers high-speed access to data at up to 300
feet from base station. 14 channels available in
the 2.4GHz band (only 11 of which can be used
in the U.S. due to FCC regulations) with only
three non-overlapping channels.
Module 3 - Wireless Local
Area Networks – Part 5
 Wireless Standards: IEEE
802.11 (A)
 Data Rate: Up to 54Mbps in the
5GHz band
 Products that adhere to this
standard are considered "Wi-Fi
Certified." Eight available
channels. Less potential for RF
interference than 802.11b and
802.11g. Better than 802.11b at
supporting multimedia voice,
video and large-image
applications in densely
populated user environments.
Relatively shorter range than
802.11b. Not interoperable with
802.11b.
Module 3 - Wireless Local
Area Networks – Part 6
 Wireless Standards: IEEE 802.11 (G)
 Data Rate: Up to 54Mbps in the 2.4GHz band
 Products that adhere to this standard are
considered "Wi-Fi Certified." May replace
802.11b. Improved security enhancements
over 802.11. Compatible with 802.11b. 14
channels available in the 2.4GHz band (only 11
of which can be used in the U.S. due to FCC
regulations) with only three non-overlapping
channels.
Module 3 - Wireless Local
Area Networks – Part 7
 Wireless Standards: 802.16 (WiMAX)
 Data Rate: Variable. Specifies WiMAX in the 10
to 66 GHz range
 Commonly referred to as WiMAX or less
commonly as WirelessMAN or the Air Interface
Standard, IEEE 802.16 is a specification for
fixed broadband wireless metropolitan access
networks (MANs)
 802.16a added suppor tfor the 2 to 11 GHz
range.
Module 3 - Wireless Local
Area Networks – Part 8
 Wireless Standards: Bluetooth
 Data Rate: Up to 2Mbps in the 2.45GHz band
 No native support for IP, so it does not support TCP/IP
and wireless LAN applications well. Not originally
created to support wireless LANs. Best suited for
connecting PDAs, cell phones and PCs in short
intervals.
 While Bluetooth was designed for ranged of about 15
feet special “Bluetooth Sniper Rifles” can listen in on
Bluetooth traffic from over a mile away if the user has a
LoS (line of sight) to the source.
 Bluetooth has been broken (encryption cracked),
assume everything you do over it is being watched by
those looking to steal your ident & bank accounts.
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Module 3 - Wireless
Local Area Networks –
Part 9
Wireless dangers.
AdHoc: At Starbucks it’s Christmas every day for
identity thieves. It’s so easy you wouldn’t believe.
What you see to the right is all it takes to
compromise the person next to you in the airport,
coffee shop, library, hotel, conference, etc..
What would happen if you had two wireless NIC’s
(network interface card) in your laptop with internet
sharing enabled between the two? What if you made
one AdHoc and named it “Free Public Wifi”? (AdHoc
wireless devices function as an AP (Access Point) &
broadcast their SSID). And for the final step what do
you think you could capture while monitoring that
wireless NIC with a packet sniffer?
Microsoft was kind enough to have AdHoc AP’s on
auto-connect anytime the SSID is seen after the first
attempt. This particular “Free Public Wifi” is the most
widely used SSID by thieves around the world. This
SSID can be found everywhere from Africa to Europe
to probably right outside your window.
Use free wifi at your own risk. You may think your
smarter than your stupid neighbor who is just leaving
his ‘Linksys’ wireless unsecured, but he may be
much, much smarter than you… capturing every
username & password of every credit card, bank
account & personal sites you log into.
Module 3 - Wireless Local Area
Networks – Part 9-LAB
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Wireless Lab:
Reset wireless router to default.
Set administrative password.
Set SSID & de-activate SSID broadcast.
Set encryption to WPA1 & choose a 25
character key.
 Set up a client & connect to the wireless router.
 Sniff the traffic.
Module 4 – Exploring the Functions
of Routing
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Before we get into the details of routing protocols & path
determination algorithms lets first examine the diagram
to the right to get a good understanding of what routing is
used for.
Take note of the different networks & their placement.
10.1.128.0, 10.1.130.0 & 10.1.129.0 are the networks that
make up the backbone.
10.1.2.0, 10.1.3.0 & 10.1.1.0 are the networks that make
up the distribution layers.
While this diagram does not specify what the subnet is,
we can assume that they are all Class C subnets of /24,
(255.255.255.0)
If Daffy sends a packet addressed for Elmer it will hit
Albuquerque first. If Albuquerque does not know that the
network 10.1.3.0 exists it will drop the packet. If the
router has been configured to forward packets destined
for anything in the range 10.1.3.0 to Seville it will do so.
Routers at the most basic functionality are merely traffic
directors that point down one road or the other depending
on where the traffic wants to go. They do this by keeping
a massive roadmap that is either programmed by an
administrator manually or discovered automatically by a
routing protocol.
In this diagram you see that a packet coming from Daffy
destined for Elmer can go out either s0 or s1. Different
routing protocols have different algorithms that
determine which route to take. This is called Path Cost
Analysis.
Module 4 – Exploring the Functions
of Routing – Part 2
Routing fundamentals:
There are 3 basic rules that you can keep in mind
while you learn that will help keep new concepts
clear.
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A router never needs to “route” a packet destined for a
network range it is directly connected to.
No two interfaces on a router can be assigned an IP
address in the same network.
A router may have MANY different IP addresses
assigned to a single interface. It is not at all uncommon
for a packet to go into an interface on one network and go
right back out again the same interface on a different
network.
Module 4 – Exploring the Functions
of Routing – Part 3
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Routing Protocol Fundamentals: Distance Vector Routing
A distance-vector routing protocol is one of the two major classes of
routing protocols used in packet-switched networks for computer
communications, the other major class being the link-state protocol. A
distance-vector routing protocol uses the Bellman-Ford algorithm to
calculate paths.
Examples of distance-vector routing protocols include RIPv1 or 2 and
IGRP. EGP and BGP are not pure distance-vector routing protocols but
their concepts are the same. In many cases, EGP and BGP are considered
DV (distance-vector) routing protocols.
A distance-vector routing protocol requires that a router informs its
neighbors of topology changes periodically and, in some cases, when a
change is detected in the topology of a network. Compared to link-state
protocols, which requires a router to inform all the nodes in a network of
topology changes, distance-vector routing protocols have less
computational complexity and message overhead.
Module 4 – Exploring the Functions
of Routing – Part 4
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Routing Protocol Fundamentals: Link-state routing
A link-state routing protocol is one of the two main classes of routing
protocols used in packet-switched networks for computer communications.
Examples of link-state routing protocols include OSPF and IS-IS.
The link-state protocol is performed by every switching node in the
network (i.e. nodes which are prepared to forward packets; in the Internet,
these are called routers). The basic concept of link-state routing is that
every node receives a map of the connectivity of the network, in the form
of a graph showing which nodes are connected to which other nodes.
Each node then independently calculates the best next hop from it for every
possible destination in the network. (It does this using only its local copy of
the map, and without communicating in any other way with any other
node.) The collection of best next hops forms the routing table for the node.
This contrasts with distance-vector routing protocols, which work by
having each node share its routing table with its neighbors. In a link-state
protocol, the only information passed between the nodes is information
used to construct the connectivity maps.
Module 4 – Exploring the Functions
of Routing – Part 5
 Routing Protocols: RIPv1 & RIPv2
 The Routing Information Protocol (RIP) is one of the most commonly
used interior gateway protocol (IGP) routing protocols on internal networks
(and to a lesser extent, networks connected to the Internet), which helps
routers dynamically adapt to changes of network connections by
communicating information about which networks each router can reach
and how far away those networks are.
 Although RIP is still actively used, it is generally considered to have been
made obsolete by routing protocols such as OSPF and IS-IS. Nonetheless,
a somewhat more capable protocol in the same basic family (distancevector routing protocols), was Cisco's proprietary (IGRP) Interior Gateway
Routing Protocol. Cisco does not support IGRP in current releases of its
software. It was "replaced" by EIGRP, the Enhanced Interior Gateway
Routing Protocol, which is a completely new design. While EIGRP is still
technically distance vector, it relates to IGRP only in having a similar name.
 RIP is sometimes said to stand for Rest in Pieces in reference to the
reputation that RIP has for breaking unexpectedly, rendering a network
unable to function.
Module 4 – Exploring the Functions
of Routing – Part 6
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Routing Protocols: RIP Continued
RIP is a distance-vector routing protocol, which employs the hop count as a routing metric. The
maximum number of hops allowed with RIP is 15, and the hold down time is 180 seconds.
Originally each RIP router transmits full updates every 30 seconds by default. Originally, routing
tables were small enough that the traffic was not significant.
As networks grew in size, however, it became evident there could be a massive burst every 30
seconds, even if the routers had been initialized at random times. It was thought, as a result of
random initialization, the routing updates would spread out in time, but this was not true in
practice. Sally Floyd and Van Jacobson published research in 1994 [1] that showed having all
routers use a fixed 30 second timer was a very bad idea. Without slight randomization of the
update timer, this research showed that the timers weakly synchronized over time and sent their
updates out at the same time. Modern RIP implementations introduce deliberate time variation
into the update timer of each router.
It runs at the network layer of the Internet protocol suite. RIP prevents routing loops from
continuing indefinitely by implementing a limit on the number of hops allowed in a path from the
source to a destination. This hop limit, however, limits the size of networks that RIP can support.
RIP implements the split horizon and holddown mechanisms to prevent incorrect routing
information from being propagated. These are some of the stability features of RIP.
In many current networking environments RIP would not be the first choice for routing as its
convergence times and scalability are poor compared to EIGRP, OSPF, or IS-IS (the latter two
being link-state routing protocols), and the hop limit severely limits the size of network it can be
used in. On the other hand, it is easier to configure because, using minimal settings for any
routing protocols, RIP does not require any parameter on a router whereas all the other protocols
require at least one or more parameters
Module 4 – Exploring the Functions
of Routing – Part 7
 Routing Protocols: RIP Continued.1
 RIPv1: defined in RFC 1058, uses classful routing. The routing
updates do not carry subnet information, lacking support for variable
length subnet masks (VLSM). This limitation makes it impossible to
have different-sized subnets inside of the same network class. In
other words, all subnets in a network class must be the same size.
There is also no support for router authentication, making RIPv1
slightly vulnerable to various attacks.
 RIPv2: Due to the above deficiencies of RIPv1, RIPv2 was
developed in 1994 and included the ability to carry subnet
information, thus supporting Classless Inter-Domain Routing
(CIDR). However to maintain backwards compatibility the 15 hop
count limit remained. Rudimentary plain text authentication was
added to secure routing updates; later, MD5 authentication was
defined in RFC 2082. Also, in an effort to avoid waking up hosts that
do not participate in the routing protocol, RIPv2 multicasts routing
updates to 224.0.0.9, as opposed to RIPv1 which uses broadcast.
Module 4 – Exploring the Functions
of Routing – Part 7-LAB
 At this time please complete Sequential Labs # 16 & Stand Alone Labs # 12. This Requires Boson
Cisco CCNA Network Simulator. Chapter reading
is included with the software.
Read the Chapters
Read the Chapters
Read the Chapters
Module 4 – Exploring the Functions
of Routing – Part 8
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Routing Concepts: Split horizon
In computer networks, distance-vector routing protocols employ the split horizon
rule which prohibits a router from advertising a route back out the interface from
which it was learned. Split horizon is one of the methods used to prevent routing
loops due to the slow convergence times of distance-vector routing protocols.
In this example A uses the path via B to reach C.
A will not advertise its route for C back to B. On the surface, this seems redundant
since B will never use A's route because it costs more than B's route to C. However, if
B's route to C goes down, B could end up using A's route, which goes through B; A
would send the packet right back to B, creating a loop. With split horizon, this
particular loop scenario cannot happen.
An additional variation of split horizon does advertise the route back to the router that
is used to reach the destination, but marks the advertisement as unreachable. This is
called split horizon with poison reverse.
Module 4 – Exploring the Functions
of Routing – Part 9
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Routing Protocols: IGRP
Interior Gateway Routing Protocol (IGRP) is a kind of IGP which is a distance-vector
routing protocol invented by Cisco, used by routers to exchange routing data within an
autonomous system.
IGRP was created in part to overcome the limitations of RIP (maximum hop count of only 15,
and a single routing metric) when used within large networks. IGRP supports multiple metrics
for each route, including bandwidth, delay, load, MTU, and reliability; to compare two routes
these metrics are combined together into a single metric, using a formula which can be
adjusted through the use of pre-set constants. The maximum hop count of IGRP-routed
packets is 255 (default 100).
IGRP is considered a classful routing protocol. As the protocol has no field for a subnet mask
the router assumes that all interface addresses have the same subnet mask as the router itself.
This contrasts with classless routing protocols that can use variable length subnet masks.
Classful protocols have become less popular as they are wasteful of IP address space.
In order to address the issues of address space and other factors, Cisco created EIGRP
(Enhanced Interior Gateway Routing Protocol). EIGRP adds support for VLSM (variable
length subnet mask) and adds the Diffusing Update Algorithm (DUAL) in order to improve
routing and provide a loopless environment. EIGRP has completely replaced IGRP, making
IGRP an obsolete routing protocol. In Cisco IOS versions 12.3 and greater, IGRP is
completely unsupported. IGRP is still taught in Cisco's CCNA curriculum, but it should be
noted that knowledge of IGRP is not tested.
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Module 4 – Exploring the Functions
of
Routing
–
Part
15
Routing Concepts: Route Summarization
Route summarization, also know as route aggregation, summarizes a group of routes into a
single route advertisement. Route summarization can be used as a powerful tool in a
networking environment. The demand for increased network capabilities has resulted from
corporate expansions and mergers. The number of subnets and network addresses
contained in routing table is rapidly increasing based on these expansions. This growth has
had a negative impact on CPU resources, bandwidth, and memory used to maintain the
routing tables. Therefore, route summarization was introduced as a way to reduce the size
of network routing tables.
If configured properly, route summarization can reduce the latency associated with router
hop, since the average speed for routing table lookup will be increased due to the reduced
number of entries. The overhead for routing protocols can also be reduced since fewer
routing entries are being advertised.
Another advantage of using route summarization in large, complex networks is that it can
isolate topology changes from other routers. This can aid in improving the stability of the
network by limiting the propagation of routing traffic after a network link goes down. For
example, if a router only advertises a summary route to the next router hop, then it will not
advertise any changes to specific subnets within the summarized range. This can
significantly reduce any unnecessary routing updates following a topology change. Hence,
increasing the speed of convergence and allowing for a more stable environment.
Module 4 – Exploring the Functions
of Routing – Part 16
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
Routing Concepts: Route Summarization Continued
As an example of how summarization can be used as a powerful tool in
a networking environment imagine a company that operates 150
accounting services in each of the 50 states and each accounting office
has a router and frame relay link connected to its corporate office.
Without route summarization, the routing table on any given router
would have to maintain 150 routers times 50 states = 7,500 different
networks. However, if route summarization is implemented, then each
state would have a centralized site to connect it with all other offices.
Since each router is summarized before being advertised to other
states, then every router will only see its own subnets and 49
summarized entries representing other states. This would create less
stress on the router’s CPU, memory, and bandwidth.
Module 4 – Exploring the Functions
of Routing – Part 17

Routing Concepts: Route Summarization
Continued.1

In order to determine the summary route on a router, you must first decide the number of
highest-order bits that match in all addresses. See the following example which shows the
process of calculating a summary route.
In the table below, Router A has the following networks in its routing table:
192.168.98.0
192.168.99.0
192.168.100.0
192.168.101.0
192.168.102.0
192.168.105.0
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

First of all, you must convert the addresses to binary format and align them in a list as
shown in the table to the right.
Second, locate the bits where the common pattern of digits ends (those in red). Lastly, count the number of
common bits. The summary route number is represented by the first IP address in the block, followed by a slash,
followed by the number of common bits.
Summarized route is 192.168.96.0/20
As you can see, the first 20 bits of the IP address are the same. Hence, the best summary route can be advertised
as 192.168.96.0/20. For summarization to work properly, multiple IP addresses must share the same highest-order
bits and should only be implemented within classless routing protocols such as EIGRP, OSPF, RIP v.2, IS-IS for IP,
and BGP.
In some cases, this feature may not be feasible. For example, in RIP v.1 is a classful routing protocol that
automatically summarizes based on class when advertising across a major network boundary. Automatic route
summarization can potentially cause problems if summarization occurs at more than one point in the network since
the summarized routes may be in conflict. When this occurs, a router receives identical summary routes from
different directions. This can lead to serious connectivity issues.
Module 5 – Wide Area Networks


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
The great Google has collected these definitions of a WAN:
A network of computers spread out across a great distance. WANs are often
networks of networks, linking local area networks into a single network.
faculty.tamu-commerce.edu/espinoza/s/carpenter-p/cl1.html
(WANs) are networks that generally span distances greater than one city
and include regional networks such as telephone companies or international
networks such as global communications services providers.
www.wiley.co.uk/college/turban/glossary.html
A wide area network or WAN is a computer network covering a wide
geographical area, involving vast array of computers. This is different from
personal area networks (PANs), metropolitan area networks (MANs) or
local area networks (LANs) that are usually limited to a room, building or
campus. The best example of a WAN is the Internet.
en.wikipedia.org/wiki/Wide_area_networks
Module 5 – Wide Area Networks – Part 2
Module 5 – Wide Area Networks – Part 3
Module 5 – Wide Area Networks –
Part 4
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PPP Encapsulation
PPP (Point-to-Point Protocol) is a protocol for communication between two
computers using a serial interface, typically a personal computer connected
by phone line to a server. For example, your Internet server provider may
provide you with a PPP connection so that the provider’s server can respond
to your requets, pass them on to the Internet, and forward your requested
Internet responses back to you. PPP uses the Internet Protocol (IP) (and is
designed to handle other). It is sometimes considered a member of the TCP/IP
suite of protocols. Relative to the Open Systems Interconnection (OSI)
reference model, PPP provides layer 2 (data-link layer) service. Essentially, it
packages your computer’s TCP/IP packets and forwards them to the server
where they can actually be put on the Internet.
PPP is a full-duplex protocol that can be used on various physical media,
including twisted pair or fiber optic lines or satellite transmission. It uses a
variation of High Speed Data Link Control (HDLC) for packet encapsulation.
PPP is usually preferred over the earlier de facto standard Serial Line Internet
Protocol (SLIP) because it can handle synchronous as well as asynchronous
communication. PPP can share a line with other users and it has error
detection that SLIP lacks. Where a choice is possible, PPP is prefered.
Module 5 – Wide Area Networks –
Part 4-LAB


At this point do Stand Alone Labs # 16 , Scenario
Labs # 10 & Sequential Lab # 15.
These labs cover PPP encapsulation & NAT/PAT
routing.
READ CHAPTER 8
&9
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