CCNA 1 Module 10

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CCNA 1 Module 10

• By Larry Twigg

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10.1.1 Routable/Routed Protocols

• A protocol is a set of rules that determines how
  computers communicate
• A protocol describes
• Format that a message must conform to
• Way computers must exchange a message within an
  activity

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10.1.1 cont

• A routed protocol allows the router to forward
  data on different networks
• IPX require only a network number
• IP requires both a network number and a host
  number.
• Network mask differentiate the two numbers
• Network numbers can be found by ANDing an IP
  Address with its network (subnet) mask

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10.1.2 IP as a Routed Protocol

• Most widely used implementation of a hierarchical
  network-addressing scheme
• Connectionless no dedicated circuit
• Unreliable does not verify that the data
  reached the destination
• Best Effort does the best to send information

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Encapsulation

• Network layer the data is encapsulated into
  packets
• IP determines the contents of the IP packet
  header which include
• Addressing information
• Control information
• IP is not concerned with the data itself

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10.1.3 Packet Propagation and Switching Within a
Router

• Layer 2 frame headers and trailers are removed
  and replaced at each Layer 3 Device
• Layer 2 Ethernet frames are designed to work
  within a broadcast domain and therefore need to
  change in each broadcast domain
• The MAC destination is used to determine if
  packet is processed or discarded
• The source MAC address is replaced at each layer
  3 device with that layer 3 devices MAC address

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Layer 2 Frame Types

• Ethernet
• PPP (Point-to-Point)
• Frame Relay

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10.1.4 Internet Protocol (IP)

• Connectionless System
• The destination is not contacted before data is
  sent
• The sender does not know if the data arrived
• Connection-oriented
• A connection is established before data is sent
• The transport layer adds TCP to IP to give the
  connection-oriented reliability services

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Switched Environment

• Packet switched Connectionless network
• Packets can take different paths
• Circuit switched Connection-oriented
• All packets go on the same path

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10.1.5 Anatomy of an IP Packet

• IP packets consist of
• Data from upper layers
• IP Header
• Version
• IP header length (HLEN)
• Type-of-service (TOS)
• Total Length
• Identification

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Anatomy (cont)

• Flags
• Fragment offset
• Time-to-live
• Protocol
• Header checksum
• Source Address
• Destination address

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Anatomy (cont.)

• Options
• Padding
• Data
• Packets are prevented from looping endlessly by
  TTL

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10.2.1 Routing Overview

• Routing is a Layer 3 (Network) function
• Routing is best path determination
• Routing functions
• Maintain Routing tables and make sure other
  routers know of topology changes
• Using routing tables, decide what is the best
  path and send out that interface
• At each router, the encapsulation and
  de-encapsulation process happens

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Other Protocols

• Routable
• IPX
• Appletalk
• Non-routable
• NetBEUI

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10.2.2 Routing Versus Switching

• The major difference between routing and
  switching is the layers.
• Switches
• Switches use MAC addresses
• Switches create Collision domains
• Routers
• Routers use IP addresses
• Routers create Broadcast domains
• Provides a higher level of security and bandwidth
  control

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Tables

• ARP tables are only effective within its
  broadcast domain. IP to MAC
• Router tables contain IP to MAC, routes and how
  they were learned
• C directly connected
• R RIP

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10.2.3 Routed versus Routing

• Routed Protocols
• Includes any network protocol suite that provides
  enough information in its network layer address
  to allow a router to forward it to the next
  device and ultimately to its destination.
• Defines the format and use of the fields within a
  packet

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Examples of Routed Protocols

• IP (Internet Protocol)
• IPX ( Novells Internetworking Packet Exchange)
• DECnet
• Appletalk
• Banyan VINES
• XNS (Xerox Network Systems)

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Routing Protocols

• Provides processes for sharing route information
• Allows routers to communicate with other routers
  to update and maintain the routing tables

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Examples of Routing Protocols

• RIP (Routing Information Protocol)
• IGRP ( Interior Gateway Routing Protocol)
• OSPF ( Open Shortest Path First)
• BGP (Border Gateway Protocol)
• EIGRP (Enhanced IGRP)

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10.2.4 Path Determination

• Occurs at the network layer.
• Enables a router to compare the destination
  address to the available routes in its routing
  table, and to select the best path.
• The routers learn of these available routes
  through static routing or dynamic routing.
• Routes configured manually by the network
  administrator are static routes.
• Routes learned by other routers using a routing
  protocol are dynamic routes.

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10.2.5 Routing Tables

• Protocol type The type of routing protocol that
  created the routing table entry
• Destination/next-hop associations How far to
  next router and which interface to send
  information
• Routing metric Different routing protocols use
  different routing metrics. Routing metrics are
  used to determine the desirability of a route.
• Outbound interfaces The interface that the data
  must be sent out on, in order to reach the final
  destination.

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Routing Algorithms

• An algorithm is a detailed solution to a problem
• Goals
• Optimization
• Simplicity and low overhead
• Robustness and stability
• Flexibility
• Rapid Convergence

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Metrics

• Routing Algorithms use different Metrics to
  determine best route
• Types of metrics
• Bandwidth
• Delay
• Load
• Reliability
• Hop Count
• Ticks
• Cost

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10.2.7 IGP and EGP

• Autonomous system is a network under the common
  administrative control
• IGPs route data within an autonomous system
• RIP , RIPv2
• IGRP
• EIGRP
• OSPF
• IS-IS
• EGPs route data between autonomous systems
• BGP

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10.2.8/9 Distance Vector

• Distance vector determines the distance and
  direction to any link in the internetwork
• Routers send routing table entries to adjacent
  routers on a periodic basis
• Routing by rumor Since the updates only go to
  adjacent routers all other paths are as good as
  to path it was received

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RIP

• Most common IGP in the Internet
• Rip uses hop count ( each router is a hop)
• Hop count is the only metric
• Selects least number of hops but not necessarily
  the fastest path
• Maximum hop count is 15
• All devices must use the same subnet mask
• Classful Routing - Does not include subnet mask
  information in routing updates

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RIP Version 2

• Uses hop count
• Classless routing Prefix routing and sends
  subnet mask information
• VLSM Variable Length Subnet Mask -different
  subnet masks on same network

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IGRP

• Cisco Proprietary
• Associated with routing in large, heterogeneous
  networks
• Metrics Delay, bandwidth, load, and reliability
• Uses only classful routing

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EIGRP

• Cisco Proprietary
• Has features of link state therefore considered
  an hybrid
• Fast convergence (all routers have same topology)
• Low overhead bandwidth

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Link-state Protocols

• Respond to network changes
• Sends updates only when the topology changes
• Link-state refreshes period updates like 30
  mins
• LSA Link-state Advertisements
• Created when topology change is detected
• Used to update routers link-state database
• Forwards all LSAs to every router and that router
  puts all the pieces together

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OSPF Open shortest Path First

• Developed by IETF (Internet Engineering Task
  Force) in 1988
• Designed for large, scalable internetworks

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IS-IS Intermediate System to Intermediate
System

• Used for non IP networks
• Integrated IS-IS supports multiple routed
  protocols including IP

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BGP Border Gateway Protocol

• Is an External Gateway Protocol (EGP)
• Exchanges routing information between autonomous
  systems
• Guarantees loop free path selection
• The principle route advertising protocol used by
  major companies and ISPs on the Internet
• BGP4 supports CIDR and route aggregation

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10.3.1 Classes of network IP addresses

• IP addresses have network bits and hosts bits
• Default Subnet Masks
• Class A 255.0.0.0
• Class B 255.255.0.0
• Class C 255.255.255.0

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Host bits

• Available Hosts bits
• Class A 24 bits
• Class B 16 bits
• Class C 8 bits
• Useable Host bits to change to Subnet bits
• Class A 22 bits
• Class B 14 bits
• Class C 6 bits

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10.3.2 Introduction to and reason for subnetting

• To create the subnetwork structure, host bits
  must be reassigned as network bits
• Reasons to subnet
• Subnetting provides flexibility
• Provide broadcast containment
• Low-level security on the LAN
• A LAN is seen as a single network keeping routing
  tables smaller

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10.3.3 Establishing the subnet mask address

• Borrow hosts bits and make them subnet bits (0
  changed to 1)
• Translate binary back to decimal
• 2 bits 192
• 3 bits 224
• 4 bits 240
• 5 bits 248
• 6 bits 252
• Slash notation numbers of ones

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Useable

• To find useable subnets 2 to the power of bits
  borrowed (1s) -2
• To find useable hosts 2 to the power of hosts
  bits left 2
• Useable table (Class C)
• 2 bits 4 2 2
• 3 bits 8 2 6
• 4 bits 16 2 14
• 5 bits 32 2 30
• 6 bits 64 2 62

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10.3.4 Applying the Subnet Mask

• Starting with 0 add the number resulting from 2
  to the power of hosts bits
• Add until you get to 256
• For the ending of each range subtract one from
  the next range starting value
• The first value of the range is the network
  number ( Host portion is all zeros)
• The last value of the range is the broadcast
  number (Host portion is all 1s)

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Subnetting example 3 bits

• 195.32.56.0/27
• 0 31
• 32 63
• 64 95
• 96 127
• 128 159
• 160 191
• 192 223
• 224 - 255

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10.3.5 Subnetting Class A and B as a Class C

• Using 255.255.255.0 with a Class A
• Useable Subnets
• 16 bits borrowed
• 8 from 2nd octet, 8 from 3rd octet
• 2 16 2 65536 2 65,534 useable subnets
• Useable Hosts
• 8 hosts bit left in 4th octet
• 2 8 256 2 254 useable hosts

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10.3.5 cont.

• Using 255.255.255.0 with a Class B
• Useable Subnets
• 8 bits borrowed from 3rd octet
• 2 8 2 256 2 254 useable subnets
• Useable Hosts
• 8 hosts bit left in 4th octet
• 2 8 256 2 254 useable hosts

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10.3.6 Boolean Logical AND

• AND Operation
• if both digits are 1s you get a 1 otherwise you
  get a 0

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Boolean Logic and Network numbers

• Given a IP address and its subnet mask you can
  determine the network number using Boolean logic.
• AND the two numbers and the result is the network
  number.
• For an example use 193.25.150.35 and subnet mask
  of 255.255.255.240.

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Boolean Logic and Network numbers (cont)

• 193.25.150.35 is
• 11000001 00011001 10010110 00100101
• 255.255.255.240 is
• 11111111 11111111 11111111 11110000
• Do an AND (both have to be 1 to get a one,
  otherwise the result is 0)
• 11000001 00011001 10010110 00100000
• Notice that where the 255 was the number is the
  original number. Change back.
• 193.25.150.32 is the network number.

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Boolean ANDing Practice 1

• Use IP address 128.17.240.80
• 10000000 00010001 11110000 01010000
• Subnet Mask 255.255.224.0
• 11111111 11111111 11100000 00000000
• AND them
• 10000000 00010001 11100000 00000000
• Answer 128.17.224.0
• Notice a 0 in submask gives a 0 in network.

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Boolean ANDing Practice 2

• IP Address 62.220.100.15 Subnet mask 255.240.0.0
• 62.208.0.0
• IP Address 220.100.62.208 Subnet mask
  255.255.255.224
• 220.100.62.192