CCNA 1 v3.0 Module 10 Routing Fundamentals and Subnets

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CCNA 1 v3.0 Module 10 Routing Fundamentals and
Subnets
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Objectives

• Routed protocol
• IP routing protocols
• The mechanics of subnetting

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Routed Protocol
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Routable and Routed Protocols

• A routed protocol allows the router to forward
  data between nodes on different networks.
• In order for a protocol to be routable, it must
  provide the ability to assign a network number
  and a host number to each individual device.
• These protocols also require a network mask in
  order to differentiate the two numbers.
• The reason that a network mask is used is to
  allow groups of sequential IP addresses to be
  treated as a single unit.

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IP as a Routed Protocol

• IP is a connectionless, unreliable, best-effort
  delivery protocol.
• As information flows down the layers of the OSI
  model the data is processed at each layer.
• IP accepts whatever data is passed down to it
  from the upper layers.

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Packet Propagation and Switching Within a Router
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Packet Propagation and Switching Within a Router

• As a frame is received at a router interface.
• The MAC address is checked to see if the frame is
  directly addressed to the router interface, or a
  broadcast.
• The frame header and trailer are removed and the
  packet is passed up to Layer 3.
• The destination IP address is compared to the
  routing table to find a match.
• The packet is switched to the outgoing interface
  and given the proper frame header.
• The frame is then transmitted.

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Internet Protocol (IP) Connectionless

• The Internet is a gigantic, connectionless
  network in which all packet deliveries are
  handled by IP.
• TCP adds Layer 4, connection-oriented reliability
  services to IP.

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Telephone Calls Connection-oriented
A connection is established between the sender
and the recipient before any data is transferred.
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Anatomy of an IP Packet

• While the IP source and destination addresses are
  important, the other header fields have made IP
  very flexible.
• The header fields are the information that is
  provided to the upper layer protocols defining
  the data in the packet.

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IP Routing Protocols
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Routing Overview

• A router is a network layer device that uses one
  or more routing metrics to determine the optimal
  path.
• Routing metrics are values used in determining
  the advantage of one route over another.
• Routing protocols use various combinations of
  metrics for determining the best path for data.

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Routing Versus Switching

• This distinction is routing and switching use
  different information in the process of moving
  data from source to destination.

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Routing Versus Switching
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Routed and Routing

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

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Path Determination

• Path determination enables a router to compare
  the destination address to the available routes
  in its routing table, and to select the best
  path.

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Routing Tables

• Routers keep track of the following
• Protocol type
• Destination/next-hop associations
• Routing metric
• Outbound interfaces

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Routing Algorithms and Metrics

• Routing protocols have one or more of the
  following design goals
• Optimization
• Simplicity and low overhead
• Robustness and stability
• Flexibility
• Rapid convergence

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IGP and EGP

• IGPs route data within an autonomous system.
• RIP, RIPv2, IGRP, EIGRP, OSPF, IS-IS
• EGPs route data between autonomous systems
• Border Gateway Protocol (BGP)

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Link State and Distance Vector

• Examples of distance-vector protocols
• Routing Information Protocol (RIP)
• Interior Gateway Routing Protocol (IGRP)
• Enhanced IGRP (EIGRP)
• Examples of link-state protocols
• Open Shortest Path First (OSPF)
• Intermediate System-to-Intermediate System (IS-IS)

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Routing Protocols

• RIP
• RIP v2
• IGRP
• EIGRP
• OSPF
• IS-IS
• BGP

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Mechanics of Subnetting
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Classes of Network IP Addresses
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Introduction to Subnetting

• Host bits must are reassigned (or borrowed) as
  network bits.
• The starting point is always the leftmost host
  bit.

3 bits borrowed allows 23-2 or 6 subnets
5 bits borrowed allows 25-2 or 30 subnets
12 bits borrowed allows 212-2 or 4094 subnets
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Reasons for Subnetting

• Provides addressing flexibility for the network
  administrator.
• Each LAN must have its own network or subnetwork
  address.
• Provides broadcast containment and low-level
  security on the LAN.
• Provides some security since access to other
  subnets is only available through the services of
  a router.

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Establishing the Subnet Mask Address

• Determines which part of an IP address is the
  network field and which part is the host field.
• Follow these steps to determine the subnet mask
• 1. Express the subnetwork IP address in binary
  form.
• 2. Replace the network and subnet portion of the
  address with all 1s.
• 3. Replace the host portion of the address with
  all 0s.
• 4. Convert the binary expression back to
  dotted-decimal notation.

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Establishing the Subnet Mask Address

• To determine the number of bits to be used, the
  network designer needs to calculate how many
  hosts the largest subnetwork requires and the
  number of subnetworks needed.
• The slash format is a shorter way of
  representing the subnet mask
• /25 represents the 25 one bits in the subnet mask
  255.255.255.128

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Establishing the Subnet Mask Address
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Subnetting Class A and B Networks

• The available bits for assignment to the subnet
  field in a Class A address is 22 bits while a
  Class B address has 14 bits.

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Calculating the Subnetwork With ANDing

• ANDing is a binary process by which the router
  calculates the subnetwork ID for an incoming
  packet.
• 1 AND 1 1 1 AND 0 0 0 AND 0 0
• The router then uses that information to forward
  the packet across the correct interface.

Packet Address 192.168.10.65 11000000.10101000.00001010.010 00001
Subnet Mask 255.255.255.224 11111111.11111111.11111111.111 00000
Subnetwork Address 192.168.10.64 11000000.10101000.00001010.010 00000
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Summary