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Routing Fundamentals and Subnets. Objectives. Routed protocol IP routing protocols The mechanics of subnetting. Routed Protocol. Routable and Routed Protocols . A routed protocol allows the router to forward data between nodes on different networks.

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Presentation Transcript
  • Routed protocol
  • IP routing protocols
  • The mechanics of subnetting
routable and routed protocols
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.
ip as a routed protocol
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.
packet propagation and switching within a router7
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.
internet protocol ip connectionless
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.
telephone calls connection oriented
Telephone Calls: Connection-oriented

A connection is established between the sender and the recipient before any data is transferred.

anatomy of an ip packet
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.
routing overview
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.
routing versus switching
Routing Versus Switching
  • This distinction is routing and switching use different information in the process of moving data from source to destination.
routed versus routing
Routed Versus 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.
path determination
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.
routing tables
Routing Tables
  • Routers keep track of the following:
    • Protocol type
    • Destination/next-hop associations
    • Routing metric
    • Outbound interfaces
routing algorithms and metrics
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
igp and egp
  • IGPs route data within an autonomous system.
  • EGPs route data between autonomous systems
    • Border Gateway Protocol (BGP)
link state and distance vector
LinkState 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)
routing protocols
Routing Protocols
  • RIP
  • RIP v2
  • IGRP
  • OSPF
  • IS-IS
  • BGP
introduction to subnetting
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

reasons for subnetting
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.
establishing the subnet mask address
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.
establishing the subnet mask address27
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
subnetting class a and b networks
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.
calculating the subnetwork with anding
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.