Routing Fundamentals and Subnets

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Routing Fundamentals and Subnets

• Module 10, Review

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10.1.2 IP as a routed protocol

• IP is a connectionless, unreliable, best-effort
  delivery protocol.

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10.1.3 Packet propagation and switching within a
router

• As a packet travels through an internetwork to
  its final destination, the Layer 2 frame headers
  and trailers are removed and replaced at every
  Layer 3 device. This is because Layer 2 data
  units, or frames, are for local addressing. Layer
  3 data units, or packets, are for end-to-end
  addressing.

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10.1.4 Internet Protocol (IP)

• TCP adds Layer 4, connection-oriented reliability
  services to IP.
• The MAC address is changed when a frame is
  received at a router interface.

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10.1.5 Anatomy of an IP Packet

• The IP header consists of the following
• Version
• IP header length (HLEN)
• Type-of-service (TOS)
• Total length Identification
• Flags
• Fragment offset.
• Time-to-live (TTL) A field that specifies the
  number of hops a packet may travel. This number
  is decreased by one as the packet travels through
  a router. When the counter reaches zero the
  packet is discarded. This prevents packets from
  looping endlessly.
• Protocol
• Header checksum
• Source address
• Destination address
• Options
• Padding
• Data

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10.2.1 Routing Overview

• The encapsulation and de-encapsulation process
  occurs each time a packet transfers through a
  router.

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10.2.2 Routing versus switching

• Switches use the ARP tables for Layer 2 MAC
  addresses and Routers use routing tables for
  Layer 3 IP addresses.
• Another difference between switched and routed
  networks is switched networks do not block
  broadcasts.
• As a result, switches can be overwhelmed by
  broadcast storms.
• Routers block LAN broadcasts, so a broadcast
  storm only affects the broadcast domain from
  which it originated.
• Since routers block broadcasts, they also provide
  a higher level of security and bandwidth control
  than switches

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10.2.3 Routed versus Routing

• Examples of routed protocols
• The Internet Protocol (IP)
• Novell's Internetwork Packet Exchange (IPX)
• DECnet
• AppleTalk
• Banyan VINES
• Xerox Network Systems (XNS).

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10.2.3 Routed versus Routing

• A routing protocol functions includes the
  following
• Provides processes for sharing topological route
  information
• Allows routers to communicate with other routers
  to update and maintain the routing tables
• Examples of routing protocols
• Routing Information Protocol (RIP)
• Interior Gateway Routing Protocol (IGRP)
• Open Shortest Path First (OSPF)
• Border Gateway Protocol (BGP)
• Enhanced IGRP (EIGRP).

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10.2.4 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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10.2.5 Routing tables

• Routers keep track of the following information
  in their routing tables
• Protocol type
• Next-hop associations
• Routing metric
• Outbound interfaces

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10.2.6 Routing Algorithms and Metrics

• The following are the metrics that are most
  commonly used by routing protocols
• Bandwidth
• Delay
• Load
• Reliability
• Hop count
• Ticks.
• Cost

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10.2.8 Link State and Distance Vector

• Examples of link-state protocols include Open
  Shortest Path First (OSPF) and Intermediate
  System-to-Intermediate System (IS-IS).
• When a route or link changes, the device that
  detected the change creates a link-state
  advertisement (LSA) concerning that link.
• Link-State refresh packet
• Topology changes

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10.2.8 Link state and distance vector

• Routing Information Protocol (RIP) The most
  common IGP in the Internet, RIP uses hop count as
  its only routing metric.

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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.
• Benefits of subnetting
• Addressing flexibility for the network
  administrator.
• Smaller broadcast domains
• Low-level security on the LAN.

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10.3.2 Introduction to and Reason for Subnetting

• Host bits of the network address are all 0
• Host bits of the broadcast address are all 1

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10.3.6 Calculating the Resident Subnetwork
through ANDing

• Routers use subnet masks to determine the home
  subnetwork for individual nodes.
• This process is referred to as logical ANDing.
• ANDing is a binary process by which the router
  calculates the subnetwork ID for an incoming
  packet.

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Subnetting Problems

• Applying the default subnet mask for a Class C
  network to a Class B network creates 254 usable
  subnets.
• 16 bits are available for Class B host IP
  addresses using the default subnet mask.
• What is the subnet mask for the subnets when you
  create 5 subnets from a Class C address?
  255.255.255.___________?

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Subnetting Problems

• Given a computer with the IP address of
  172.32.65.13 and a default subnet mask what is
  the network address of this computers network?