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ICND -1 Interconnecting Cisco Networking Devices Assembled By David Roberts

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Title: ICND -1 Interconnecting Cisco Networking Devices Assembled By David Roberts


1
ICND -1 Interconnecting Cisco Networking Devices
Assembled By David Roberts
  • Knowing what you DONT know is more important
    than what you DO know. It takes both to have
    expertise.

2
Course Content
  • 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.

3
Course Objectives
  • 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
    routers startup and configuration .

4
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

5
Module 1 - Building a Simple Network
  • Connect 3 PCs 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.)
6
Module 1 - Building a Simple Network Part 2
  • With the Class A IPs 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 PCs?

7
Module 1 - Building a Simple Network Part 3
  • Reset all PCs to the Class C addressing scheme
  • 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)
  • 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 PCs 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 PCs?

8
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.
9
Module 2 - Ethernet Local Area Networks Part 2
  • 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

10
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-or-nothing 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.
11
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.
  • 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.

12
Module 2 - Ethernet Local Area Networks Part 5
  • 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 half-duplex
    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.

13
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.
14
Module 2 - Ethernet Local Area Networks Part 7
Crossover cables are used when connecting two
PCs or switches directly together. Most network
equipment manufactured within the last two years
has auto X-over negotiation built into the device.
Console Cables are used to directly connect to
management interfaces (serial port) on network
equipment.
15
Module 2 - Ethernet Local Area Networks Part 8
Example of unshielded twisted pair (top)
shielded twisted pair (bottom).
Your basic RJ-45 tip crimp tool.
16
Module 2 - Ethernet Local Area Networks Part
8-LAB
  • 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 PCs.

17
Module 3 - Wireless Local Area Networks
  • 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.

18
Module 3 - Wireless Local Area Networks Part 2
  • 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
    havent 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 computers
    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 IEEEs
    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 doesnt 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.

19
Module 3 - Wireless Local Area Networks Part 3
  • 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
    AES-based 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.

20
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.

21
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.

22
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.

23
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.

24
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.

25
Module 3 - Wireless Local Area Networks Part 9
  • Wireless dangers.
  • AdHoc At Starbucks its Christmas every day for
    identity thieves. Its so easy you wouldnt
    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 NICs
    (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 APs 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.

26
Module 3 - Wireless Local Area Networks Part
9-LAB
  • 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.

27
Module 4 Exploring the Functions of Routing
  • 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.

28
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.
  • 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.

29
Module 4 Exploring the Functions of Routing
Part 3
  • 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.

30
Module 4 Exploring the Functions of Routing
Part 4
  • 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.

31
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 (distance-vector 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.

32
Module 4 Exploring the Functions of Routing
Part 6
  • 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

33
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.

34
Module 4 Exploring the Functions of Routing
Part 7-LAB
  • At this time please complete Sequential Labs
    1-6 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

35
Module 4 Exploring the Functions of Routing
Part 8
  • 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.
36
Module 4 Exploring the Functions of Routing
Part 9
  • 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.

37
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.

38
Module 4 Exploring the Functions of Routing
Part 16
  • 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 routers CPU, memory, and
    bandwidth.

39
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
  • 192.168.98.0 192.168.99.0 192.168.100.0 192.168.10
    1.0 192.168.102.0 192.168.105.0
  • 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.
40
Module 5 Wide Area Networks
  • 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/carp
    enter-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_network
    s

41
Module 5 Wide Area Networks Part 2
42
Module 5 Wide Area Networks Part 3
43
Module 5 Wide Area Networks Part 4
  • 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 providers
    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
    computers 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.

44
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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