Chapter 6 – Sections & Objectives

• 6.1 Network Layer Protocols
  • Describe the purpose of the network layer in data communication.
  • Explain why the IPv4 protocol requires other layers to provide reliability.
  • Explain the role of the major header fields in the IPv4 and IPv6 packet.
• 6.2 Routing
  • Explain how a host device uses routing tables to direct packets to itself, a local destination, or a default gateway.
  • Compare a host routing table to a routing table in a router.
• 6.3 Routers
  • Describe the common components and interfaces of a router.
  • Describe the boot-up process of a Cisco IOS router.
• 6.4 Configure a Cisco Router
  • Configure initial settings on a Cisco IOS router.
  • Configure two active interfaces on a Cisco IOS router.
  • Configure devices to use the default gateway.

6.1 Network Layer Protocols

Network Layer in Communications

• The Network Layer
  • End to End Transport processes
  • Addressing end devices
  • Encapsulation
  • Routing
  • De-encapsulating
• Network Layer Protocols
  • IPv4
  • IPv6

Characteristics of the IP Protocol

• Encapsulating IP
  • Segments are encapsulated into IP packets for transmission.
  • The network layer adds a header so packets can be routed to the destination.
• IP – Connectionless
  • Sender doesn’t know if the receiver is listening or the message arrived on time.
  • Receiver doesn’t know data is coming.
• IP – Best Effort Delivery
  No guarantees of delivery are made.
• IP – Media Independent
  • IP can travel over different types of media.

IPv4 Packet

• • IPv4 Packet Header

• Version = 0100
• DS = Packet Priority
• TTL = Limits life of Packet
• Protocol = Upper layer protocol such as TCP
• Source IP Address = source of packet
• Destination IP Address = destination of packet

IPv6 Packet

• Limitations of IPv4
  • IP address depletion
  • Internet routing table expansion
  • Lack of end-to-end connectivity
• Introducing IPv6
  • Increased address space
  • Improved packet handling
  • Eliminates the need for NAT
• EncapsulatingIPv6
  • Simplified header format
  • No checksum process requirement
  • More efficient Options Header mechanism
  • Flow Label field makes it more efficient.
• IPv6 Packet Header
  – xx

IPv6 Packet (Cont.)

• • IPv6 Packet Header
    – xx

• Version = 0110
• Traffic Class = Priority
• Flow Label = same flow will receive same handling
• Payload Length = same as total length
• Next Header = Layer 4 Protocol
• Hop Limit = Replaces TTL field

6.2 Routing

How a Host Routes

• Host Forwarding Decision
  • Three types of destination: itself, local host, remote host.
• Default Gateway
  • Routes traffic to other networks
  • Has a local IP address in the same address range as other hosts on the network
  • Can take data in and forward data out
• Using the Default Gateway
  • Hosts will use the default gateway when sending packets to remote networks.
• Host Routing Tables
  • Use the netstat –r command to display the
  • host routing table on a Windows machine.

How a Host Routes Router Routing Tables

• Router Packet Forwarding Decision
  • Routers and hosts forward packets in a similar fashion.
  • The main difference is that routers have more interfaces while hosts often have only one.
  • Devices on directly connected networks can be reached directly.
  • Devices on remote networks are reached through gateway.
• IPv4 Router Routing Table
  • The router routing table stores network routes the router knows about.
  • Use the show ip route command to display the routing table on a Cisco router.
  • The router routing table also has information on: how the route was learned, its trustworthiness and rating.
  • It also contains which interface to use to reach that specifc destination.
• Directly Connected Routing Table Entries
  • C – Identifies a directly-connected network, automatically created when an interface is configured with an IP address and activated.
  • L – Identifies that this is a local interface. This is the IPv4 address of the interface on the router.
• Remote Network Routing Table Entries
• Remote Network Routing Table Entries
  • Remote destinations can’t be reached directly.
  • Remote routes contain the address of the intermediate network device to be used to reach the destination.
• Next-Hop Address
  Next-Hop address is the address of the intermediate device used to reach a specifc remote destination.

6.3 Routers

Anatomy of a Router

• A Router is a Computer
  • Routers have CPU, memory and I/O devices
  • Cisco routers use IOS as their operating system.
• Router Memory
  • Just as a computer, routers have memory.
  • Routers contain RAM, ROM, NVRAM and Flash memory.
• Inside a Router
  • Routers have the same general structure.
• Connect to a Router
  • Routers have may ports to support connections.
• LAN and WAN Interfaces
  • Routers have LAN and WAN ports.
  • Different models ship with different ports.
  • Ethernet is very common on different router models.

Anatomy of a Router

• Bootset Files
  • IOS image file, stored in the Flash, contains the IOS.
  • The Flash also stores other system files.
  • The NVRAM stores configuration parameters.
• Router Bootup Process
  • Perform the POST and load the bootstrap program.
  • Locate and load the Cisco IOS software.
  • Locate and load the startup configuration file or enter setup mode
• Show Version Output
  • The show version command is very useful.
  • It provides information on the amounts of memory installed, what IOS images was loaded during boot and more.

6.4 Configuring a Cisco Router

Configure Initial Settings

Configure Interfaces

• • Configure Router Interfaces
  • Enter the interface sub-configuration mode.
  • Add a description to the Interface (optional)
  • Configure an IPv4 or IPv6 address.
  • Activate the interface with a no shutdown command
• Verify Interface Configuration
  • show ip route – Displays the contents of the IPv4 routing table stored in RAM.
  • show interfaces – Displays statistics for all interfaces on the device.
  • show ip interface – Displays the IPv4 statistics for all interfaces on a router.

Configure the Default Gateway

• • Default Gateway for a Host

• Default Gateway for a Switch
  • A default gateway is required for remote network communication.
  • If a switch is to be managed via its VTY lines, it needs a default gateway.
  • Use the ip default-gateway command to configure the default gateway for a switch.

6.5 Chapter Summary

Summary

• Explain how network layer protocols and services support communications across data networks.
• Explain how routers enable end-to-end connectivity in a small to medium-sized business network.
• Explain how devices route traffic in a small to medium-sized business network.
• Configure a router with basic configurations.

Section 6.1 New Terms and Commands

Section 6.2 New Terms and Commands

Section 6.3 New Terms and Commands

Section 6.4 New Terms and Commands

• interface type-and-number
• ip address ipv4-address subnet-mask
• description description-text
• no shutdown
• show ip interface brief
• ping ip address
• show ip route
• show interfaces
• show ip interface brief
• ip default-gateway ip-address

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