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Chapter 6 - Network Layer

6.0 Network Layer

6.0.1 Introduction >6.0.1.1 Introduction

Upon completion of this chapter you will be able to:

  • Describe the purpose of network layer in data communiucation.
  • Explain why the IPv4 protocol requires other layers to provide reliability.
  • Explain the role of major header fields in the IPv4 and IPv6 packets.
  • Explain how host devices use 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.
  • Describe the common components and interfaces of a router.
  • Describe the boot-up process of a Cisco IOS router
  • Configure initial settings on a Cisco IOS router.
  • Configure two active interfaces on a Cisco IOS router.
  • Configure the default gateway on network devices.

6.0.1 Introduction >6.0.1.2 Activity – The Road Less Travelled

Figure shows a user at a computer connected to a cloud made up of 5 routers. The cloud is connected to a server at the other end. This figure demonstrates how routers inspect the destination IP address to direct packets along the correct path:

  • Many paths may be used for a single communication as individual packets are routed to a destination.
  • No fixed path is established. Packets are routed according to the best path available at the time.
  • At the destination, packets may be reassembled into order according to their sequence number.

The Network Layer uses four basic processes:

  • Addressing end devices
  • Encapsulation
  • Routing
  • De-encapsulation

6.1 Network Layer Protocols

6.1.1 The Network Layer in Communication >6.1.1.1 The Network Layer

The animation on this page demonstrates how data generated by an application on Host A is encapsulated into different PDU's as it travels down the OSI model to be transported across the network. Then it demonstrates the de-encapsulation process when it arrives at Host B. This process is explained in the page notes.

6.1.1 The Network Layer in Communication >6.1.1.2 Network Layer Protocols

The figure on this page shows the OSI model with layer 3, the Network Layer highlighted. Layer 3 has a callout showing the two primary protocols of this layer:

  • Internet Protocol version 4 (IPv4)
  • Internet Protocol version 6 (IPv6)

6.1.2 Characteristics of the IP Protocol >6.1.2.1 Characteristics of IP

The figure on this page shows 2 routers connected to a cloud. Each router has a layer 3 packet above it. The layer 3 packet is made up of the layer 4 segment and the layer 3 header.

The description given for this figure is "IP packets flow through the internetwork.".

6.1.2 Characteristics of the IP Protocol >6.1.2.2 IP – connectionless

Figure 1 on this page shows a standard letter being placed into a mailbox with a truck delivering the letter to a house. This demonstrates the similarities between Internet communications and the postal service.

The sender doesn't know:

  • If the receiver is present
  • If the letter arrived
  • If the receiver can read the letter

The receiver doesn't know:

  • When it is coming

Figure 2 on this page shows two computers connected to a network and a layer 3 packet traversing the network.

The sender doesn't know:

  • If the receiver is present
  • If the packet arrived
  • If the receiver can read the packet

The receiver doesn't know:

  • When it is coming

6.1.2 Characteristics of the IP Protocol >6.1.2.3 IP – Best Effort Delivery

The figure on this page shows two computers connected to a cloud. The sender is placing three packets on the wire, however, only two packets arrive at the destination:

  • Packets are routed through the network quickly
  • Some packets may be lost en route

The description given for this figure is "As an unreliable network protocol, IP does not guarantee that all sent packets will be received. Other protocols manage the process of tracking packets and ensuring their delivery.".

6.1.2 Characteristics of the IP Protocol >6.1.2.4 IP – Media Independent

The figure on this page shows a network with different media at each hop:

  • Copper Ethernet
  • Copper Serial
  • Optical Fiber
  • Copper Ethernet
  • Wireless

An IP packet has no trouble with this because IP is media independent.

The description given for this figure is "IP packets can travel over different media.".

6.1.2 Characteristics of the IP Protocol >6.1.2.5 Encapsulating IP

Figure 1 on this page shows a Transport layer PDU, the segment, as the segment header and the data from the upper layers.

The description given for this figure is, "The Transport layer adds a header so segments can be reassembled at the destination.".

Figure 2 on this page shows how layer 3, the Network layer, encapsulates the transport layer PDU into a packet and adds the IP Header.

The description given for this figure is, "The Network Layer adds a header so packets can be routed through complex networks and reach their destination. In TCP/IP based networks, the network layer PDU is the IP packet.".

6.1.2 Characteristics of the IP Protocol >6.1.2.6 Activity – IP Characteristics

The interactive activity on this page allows the learner to match several IP characteristics with the correct delivery method: Connectionless, Best Effort Delivery and Media Independent.

The delivery methods are:

ConnectionlessBest EffortMedia Independent

The characteristics are:

Does not guarantee that the packet will be delivered fully without errors
Will send a packet even if the destination host is not able to receive it
Will adjust the size of the packet sent depending on what type of network access will be used
No contact is made with the destination host before sending a packet
Fiber optics cabling, satellites, and wireless can all be used to route the same packet
Packet delivery is not guaranteed

6.1.3 IPv4 Packet >6.1.3.1 IPv4 Packet Header

The figure on this page shows a sample IP Header with several fields Highlighted:

Byte 1 Byte 2 Byte 3 Byte 4  
Version Internet
Headeer
Length
Differentiated Services
(DS)
Total Length 20
Bytes
DSCP ECN
Identification Flag Fragment Offset
Time-to-Live Protocol Header Checksum
Source IP Address
Destination IP Address
Options (optional) Padding  

The highlighted fields as described in the page notes are:

  • Version
  • Differentiated Services (DS)
  • Time-to-Live
  • Protocol
  • Source IP Address
  • Destination IP Address

6.1.3 IPv4 Packet >6.1.3.2 IPv4 Header Fields

The figure on this page shows the same sample IP header as the previous page with several other fields highlighted. These fields are used for validation and reordering the packets at the destination. The highlighted fields as described in the page notes are:

  • Internet header Length
  • Total Length
  • Header Checksum
  • Identification
  • Flags
  • Fragment Offset'

6.1.3 IPv4 Packet >6.1.3.3 Sample IPv4 Headers

Figure 1 on this page displays the contents of packet number 2 in a sample Wireshark capture.

Figure 2 on this page displays the contents of packet number 8 in a sample Wireshark capture. This is an HTTP packet.

Figure 3 on this page displays the contents of packet number 16 in a sample Wireshark capture. The sample packet is a ping request from host 192.168.1.109 to host 192.168.1.1.

All three figures are described in the page notes.

6.1.3 IPv4 Packet >6.1.3.4 Activity - IPv4 Header Fields

Figure 1 on this page is an interactive activity that allows the learner to match several IPv4 Header Functions with the correct IPv4 Header Field.

The IPv4 Header Fields are:

VersionDifferentiated Services
Time-to-LiveProtocol
Source IP AddressDestination IP Address

The IPv4 Header Functions are:

Identifies the upper layer protocol to be used next
Identifies the IP address of the sending host
Identifies the priority of each packet
Commonly referred to as hop count
Identifies the IP address of the recipient host
Always set to 0100 for IPv4

Figure 2 on this page is an interactive activity that allows the learner to match several IPv4 Identification and Validation Header Descriptions with the correct IPv4 Header Field.

The IPv4 Header Fields are:

Internet Header Length
Total Length
Header Checksum

The IPv4 Identification and Validation Header Descriptions are:

Maximum value is 65,535 bytes
Identifies the number of 32 – bits words in the header
Error-checks the IP header – if incorrect, the packet is discarded

6.1.4 IPv6 Packet >6.1.4.1 Limitations of IPv4

The image on this page shows a fuel gauge with the needle pointing to Empty to show that we are out of IPv4 addresses.

6.1.4 IPv6 Packet >6.4.1.2 Introducing IPv6

The table on this page shows number names from One Thousand to One Undecillion. The table includes a column for the name, a column with scientific notation and a column showing a 1 with a number of zeros. Undecillion is a 1 with 36 zeros or ten raised to the 36th power:

Number NameScientific
Notation
Number of Zeros
1 Thousand10^31,000
I Million10^61,000,000
I Billion10^91,000,000,000
1 Trillion10^121,000,000,000,000
1 Quadrilliom10^151,000,000,000,000,000
1 Quintillion10^181,000,000,000,000,000,000
1 Sextillion10^211,000,000,000,000,000,000,000
1 Septillion10^241,000,000,000,000,000,000,000,000
1 Octillion10^271,000,000,000,000,000,000,000,000,000
1 Nonillion10^301,000,000,000,000,000,000,000,000,000,000
1 Decillion10^331,000,000,000,000,000,000,000,000,000,000,000
1 Undecillion10^361,000,000,000,000,000,000,000,000,000,000,000,000

The legend states that:

  • There are 4 billion IPv4 addresses
  • There are 340 undecillion IPv6 addresses

6.1.4 IPv6 Packet >6.1.4.3 Encapsulating IPv6

Figure 1 on this page on this page shows an IPv4 header:

Version IHL Type of Service Total Length
Identification Flags Fragment Offset
Time-to-Live Protocol Header Checksum
Source IP Address
Destination IP Address
Options (optional) Padding

There are fields shaded in either:

  • Yellow that were kept in IPv6
  • Green that were renamed or repositioned in IPv6
  • Grey that were not kept in IPv6
KeptRenamed or
Repositioned
Not
Kept
VersionType of
Service
IHL
Source AddressTotal LengthIdentification
Destination AddressTime-to-LiveFlags
 ProtocolFragment Offset
  Header Checksum
  Options
  Padding

Figure 2 on this page on this page shows an IPv6 header:

Version Traffic Class Flow Label
Payload Length Next Header Hop Limit
Source IP Address
Destination IP Address

6.1.4 IPv6 Packet >6.1.4.4 IPv6 Packet Header

Figure shows an I.P. version 6 header with the following fields: Version, Traffic Class, Flow Label, Payload Length, Next Header, Hop Limit, Source Address and Destination Address.

Byte 1 Byte 2 Byte 3 Byte 4  
Version Traffic Class Flow Label 40
Bytes
Payload Length Next Header Hop Limit
Source IP Address
Destination IP Address

6.1.4 IPv6 Packet >6.1.4.5 Sample IPv6 Header

Figure 1 on this page displays the contents of packet number 46 in a sample Wireshark capture. The packet contains the initial message of the TCP 3-way handshake between an IPv6 host and an IPv6 server.

Figure 2 on this page displays the contents of packet number 49 in this sample Wireshark capture. The packet contains the initial HyperText Transfer Protocol (HTTP) GET message to the server.

Figure 3 on this page displays the contents of packet number 1 in this sample capture. The sample packet is an ICMPv6 Neighbor Solicitation message.

6.1.4 IPv6 Packet >6.1.4.6 Activity – IPv6 Header Fields

This interactive activity allows the learner to match the description with the names of the I.P. version 6 header fields.

Figure 1 on this page is an interactive activity that allows the learner to match IPv6 Header Descriptions with the correct IPv6 Header Field.

The Pv6 Header Field are:

VersionPayload Length
Traffic ClassNext Header
Flow LabelHop Limit

The IPv6 Header Descriptions are:

Identifies the application type to the upper-layer protocol
Is always set to 0110
Can be set to use the same pathway flow so that packets are not reordered upon delivery
Identifies the packet fragment size
Classifies packets for congestion control
When this value reaches 0, the sender is notified that the packet was not delivered

6.2 Routing

6.2.1 How a Host Routes >6.2.1.1 Host Forwarding Decision

The figure on this page shows router R1 connected to a LAN with two hosts, PC1 and PC2, and the Internet with a remote server. There is an arrow from PC1 to PC2 on the same network. There is also an arrow from PC1 to the remote server.

6.2.1 How a Host Routes >6.2.1.2 Default Gateway

The figure on this page shows router R1 connected to a LAN with two hosts, PC1 and PC2, and the Internet with a remote server. Router R1 has a callout saying, "The IP address of the R1 interface is the default gateway address for PC1 and PC2.".

6.2.1 How a Host Routes >6.2.1.3 IPv4 Host Routing Table

The figure on this page shows a network with the output of netstat -r command on a PC. This command shows the following IPv4 routing table for the PC. Row numbers have been added for description purposes:

C:\Users\PC1>netstat –r
<Output omitted>
IPv4 Route Table
Active Routes:
Line
Number
Network
Destination
NetmaskGatewayInterfaceMetric
10.0.0.00.0.0.0192.168.10.1192.168.10.1025
2127.0.0.0255.0.0.0On-Link127.0.0.1306
3127.0.0.1255.255.255.255On-Link127.0.0.1306
4127.255.255.255255.255.255.255On-link127.0.0.1306
5192.168.10.0255.255.255.0On-link192.168.10.10281
6192.168.10.10255.255.255.255On-Link192.168.10.10281
7 192.168.10.255255.255.255.255On-Link192.168.10.10281
8224.0.0.0240.0.0.0On-Link127.0.0.1306
9224.0.0.0240.0.0.0On-Link192.168.10.10281
10255.255.255.255255.255.255.255On-link127.0.0.1306
11255.255.255.255255.255.255.255On-link192.168.10.10281

<Output omitted>

6.2.1 How a Host Routes >6.2.1.4 IPv4 Host Routing Entries

The figure on this page shows the same IPv4 routing table as the previous page with the network destinations grouped and highlighted with different colors:

  • Row 1, the default gateway is highlighted in yellow
  • Rows 2 - 4, the loopback addresses are highlighted in green
  • Rows 5 - 7, the LAN addresses (host address, LAN network I.D. and LAN broadcast address) are highlighted in purple
  • Rows 8 and 9, the multicast addresses are highlighted in pink
  • Rows 10 and 11, the broadcast addresses are highlighted in orange

6.2.1 How a Host Routes >6.2.1.5 Sample IPv4 Host Routing Table

Figure 1 on this page shows the he same IPv4 routing table as the previous page and how the PC uses the routing table to determine how to forward a packet to a destination. The PC is trying to send a packet to a computer on the same LAN. The network address, row 5 is highlighted in the routing table. Since the destination IP address is on the same LAN as the PC, it determines that it will forward the packet out the LAN interface on the PC.

Figure 2 on this page shows the he same IPv4 routing table as the previous page and how the PC uses the routing table to determine how to forward a packet to a destination. The PC is trying to send a packet to a computer on a different network. The PC is not aware of the destination so the default gateway, row 1 is highlighted. The packet will be forwarded to the router's LAN interface.

6.2.1 How a Host Routes >6.2.1.6 Sample Ipv6 Host Routing Table

The figure on this page shows a network with the output of netstat -r command on a PC. This command shows the following IPv6 routing table for the PC:

C:\Users\PC1>netstat –r
<Output omitted>
IPv6 Route Table
Active Routes:
IfMetricNetwork DestinationGateway
1658::/0On-Link
1306::1/128On-Link
16582001::/32On-Link
163062001:0:9d38:953c:2c30:3071:e718:a926/128On-link
15281fe80::/64On-link
16306fe80::/64On-link
16306fe80::2c30:3071:e718:e926/128On-Link
15281fe80::b1ee:c4ae:a117:271f/128On-Link
1306ff00::/8On-Link
16306ff00::/8On-Link
15281ff00::/8On-Link

<Output omitted>

6.2.1 How a Host Routes >6.2.1.7 Activity – Identify Elements of a Host routing Table Entry

This interactive activity on this page allows the learner to match the appropriate description of a column in the output of the IPv4 routing table with the column name.

The following partial host routing table entry is shown. Each column of the table is identified by the column headings A - E:

C:\Documents and Settings\cisco>netstat –r
Route Table
<Output omitted>
Active Routes:
ABCDE
Network
Destination
NetmaskGatewayInterfaceMetric
0.0.0.00.0.0.0192.168.1.1192.168.10.10020
127.0.0.0255.0.0.0127.0.0.1127.0.0.11
192.168.1.0255.255.255.0192.168.10.100192.168.10.10020
192.168.10.100255.255.255.255127.0.0.1127.0.0.120

Match the correct routing table entry column for each output statement below:

  1. The physical interfaces IP address used to send the packet to the gateway
  2. The route cost – lower numbers are best
  3. The reachable networks available
  4. The network address is found in this column
  5. Used to determine the network portion of an IP address
  6. The IP address of the device that can send the packet beyond the local network

6.2.2 Router Routing Tables >6.2.2.1 Router Packet Forwarding Decision

The figure on this page shows two routers, R1 and R2 connected by a serial connection. Each router has two LANs attached. This figure shows that a router has its own routing table to consult should a packet be destined for a remote network. The routing table consists of directly connected networks and remote networks.

The network IP addresses connected to R1 are:

Directly
Connected
Remote
Networks
192.168. 10.0/2410.1.1.0/24
192.168.11.0/2410.1.2.0/24
209.165.200.224/30 

R1 has three directly connected networks: 192.168.10.0/24, 192.168.11.0/24, and 209.165.200.224/30. R1 also has two remote networks that it can learn about from R2: 10.1.1.0/24 and 10.1.2.0/24.

6.2.2 Router Routing Tables >6.2.2.2 IPv4 Router Routing Table

The figure on this page shows two routers connected by a serial connection. Each router has two LAN's attached. The following output from show ip route is displayed for one of the routers. The output contains all networks that this router has in its routing table. They include the directly connected networks, denoted by a "C" in the routing table and the remote networks, denoted by a different code depending on the routing protocol running on the router. This router is running EIGRP so the code is a "D". For each directly connected network there are 2 entries. One with a code of "C" and one with a code of "L". The "L" is new as of IOS 15 and refers to local networks:

R1#show ip route
Codes: L – local, C – connected, S- static, R – RIP, M – mobile, B – BGP
      D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
      N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
      E1 – OSPF external type 1,E2 – OSPF external type 2, E - EGP
      I – IS-IS, L1 – IS-IS level-1, L2 – IS-IS level-2, ia –
      IS-IS inter area
      * – candidate default, U – per-user static route, O – ODR
      P – periodic downloaded static route
Gateway of last resort is not set
    10.0.0.0/8 is variable subnetted, 2 subnet, 2 masks
D     10.1.1.0/24 [90/2710112] via 209.165.200.226, 00:00:05,
    Serial 0/0/0
D     10.1.1.0/24 [90/2710112] via 209.165.200.226, 00:00:05,
    Serial 0/0/0

    192.168.10.0/24 is variably subnetted, 2 subnets, 3 masks
C     192.168.10.0/24 is directly connected, GigabitEthernet0/0
L     192.168.10.1/32 is directly connected, GigabitEthernet0/0
    192.168.11.0/24 is variably subnetted, 2 subnets, 3masks
C     192.168.11.0/24 is directly connected, GigabitEthernet0/1
L     192.168.11.1/32 is directly connected, GigabitEthernet0/1
    209.165.200.0/24 is variably subnetted, 2 subnets, 3masks
C     209.165.200.224/30 is directly connected, Serial0/0/0
L     209.165.200.225/32 is directly connected, Serial0/0/0
R1#

6.2.2 Router Routing Tables >6.2.2.3 Directly connected Routing Table Entries

The figure on this page shows a network and the following small portion of the routing table from a router:

ABC
C192.168.10.0/24 is directly connected,GigabitEthernet0/0
L192.168.10.1/32 is directly connected,GigabitEthernet0/0

Legend:

  • Column A identifies how the network was learned by the router.
  • Column B identifies the destination network and how it is connected.
  • Column C identifies the interface through which the router reaches the destination network.

6.2.2 Router Routing Tables >6.2.2.4 Remote Network Routing Table Entries

The figure on this page shows a network and the following small portion of the routing table from a router:

ABCDEFG
D10.1.1.0/24[90/2170112]via 209.165.200.22600:00:05,Serial0/0/0

Legend:

  • Column A identifies how the network was learned by the router.
  • Column B identifies the destination network.
  • Column C identifies the administrative distance (trustworthiness) of the route source.
  • Column D identifies the metric to reach the remote network.
  • Column E identifies the next hop IP address to reach the remote network.
  • Column F identifies the amount of elapsed time since the route was last heard from.
  • Column G identifies the outgoing interface on the router to reach the destination network.

6.2.2 Router Routing Tables >6.2.2.5 Next-Hop Address

The figure on this page shows two routers connected by a serial connection. Each router has two LANs attached. The output from show i p route is displayed for one of the routers. The two routes learned by EIGRP have the next hop interface highlighted in orange. The next hop is the IP address of the WAN interface on the remote router.

6.2.2 Router Routing Tables >6.2.2.6 Sample Router IPv4 Routing Table

The four figure on this page illustrate four examples, as described in the page notes, of how a host and a router make packet routing decisions by consulting their respective routing tables. Each figure shows two routers connected by a serial connection. Each router has two LANs attached. The output from show i p route is displayed for one of the routers.

6.2.2 Router Routing Tables >6.2.2.7 Activity – Identify Elements of a Router Routing Table Entry

This interactive activity on this page allows the learner to match each column in the routing table with its description.

The following partial router routing table entry is shown. Each section of the entry is identified by a letter above it:

ABCDEF
D192.168.1.0/24[90/3072]via 192.168.3.1,00:06:03,GigabitEthernet0/0

The learner is asked to match the correct routing table entry section for each of the following outputs:

  1. The elapsed time since the network was discovered.
  2. The administrative distance (source) and metric to reach the remote network.
  3. How the network was learned by the router.
  4. Shows the destination network.
  5. The next hop IP address to reach the remote network.
  6. The outgoing interface on the router to reach the detonation network.

6.2.2 Router Routing Tables >6.2.2.8 Lab – View Host Routing Tables

See Lab Descriptions.

6.3 Routers

6.3.1 Anatomy of a Router >6.3.1.1 A Router is a Computer

The image on this page shows different types of routers. They include Branch routers, WAN routers and Service Provider routers.

6.3.1 Anatomy of a Router >6.3.1.2 Router CPU and OS

The image on this page shows a logic board of a 1941 router. The C.P.U. is highlighted.

6.3.1 Anatomy of a Router >6.3.1.3 Router Memory

The table on this page describes the different storage components of a router:

MemoryVolatile/Non-VolatileStores
RAMVolatile* Running IOS
* Running configuration file
* IP routing and ARP tables
* Packet buffer
ROMNon- Volatile* Bootup instructions
* Basic diagnostic software
* Limited IOS
NVRAMNon- Volatile* Startup configuration file
FlashNon-Volatile* IOS
* other system files

6.3.1 Anatomy of a Router >6.3.1.4 Inside a Router

This interactive activity on this page shows an image of the inside of a Cisco 1841 first generation ISR. Some of the components are highlighted and when you click them a brief description is displayed.

The component locations and descriptions are as follows:

  • At the top left corner of the router is the power supply.
  • Right below the power supply is the fan.
  • To the right of the power supply is the shield for WAN interface card WIC or high-speed WIC (HWIC).
  • Below the shield for the WAN is the synchronous dynamic RAM (SDRAM) used for holding the running configuration and routing tables, and for supporting packet buffering.
  • To the right of the SDRAM is the nonvolatile RAM (NVRAM) and boot flash memory used for storing the ROMMON boot code as well as NVRAM data.
  • To the right of the nonvolotile RAM is the CPU.
  • Below the CPU is the Advanced Integration Module (AIM) option that offloads processor-intensive functions such as encryption from the main CPU.
  • At the top right corner of the router is another shield for WAN interface card WIC or high-speed WIC (HWIC).

6.3.1 Anatomy of a Router >6.3.1.5 Router Backplane

The image on this page shows a picture of the rear of a Cisco 1941 router with the ports highlighted as listed below:

  • Double-wide EHWIC slots
  • Two 4 GB flash card slots
  • EHWIC 0
  • Console USB mini-B
  • AUX port
  • Console RJ-45
  • LAN interfaces
  • USB ports

6.3.1 Anatomy of a Router >6.3.1.6 Connecting to a Router

The image on this page shows a picture of the rear of a Cisco 1941 router with the inband interfaces and management ports highlighted.

The inband interfaces include:

  • WAN interface
  • LAN interface

The management ports include:

  • Console RJ-45
  • AUX port
  • Console USB type B

6.3.1 Anatomy of a Router >6.3.1.7 LAN and WAN Interfaces.

The image on this page shows a picture of the rear of a Cisco 1941 router with the WAN and LAN interfaces highlighted. These interfaces are used for remote access via Telnet or SSH and are common ways of accessing CLI on a router.

6.3.1 Anatomy of a Router >6.3.1.8 Activity – Identify Router Components

The interactive activity on this page allows the learner to match router components with their description.

The learner is asked to match the router component name to its function/description.

The router hardware parts are:

  • WAN interface
  • AUX port
  • LAN interface
  • Telnet or SSH
  • Console port

The router functions are:

Function/Description
Connects routers to external networks, usually over a large distance
A way to remotely access the CLI across network interface
Connects computers, switches, and routers for internal networking
A local port which usex USB or low-speed, serial connections to manage network devices
A port to manage routers – using telephone lines and modems

6.3.1 Anatomy of a Router >6.3.1.9 Lab – Exploring Router Physical Characteristics

See Lab Descriptions.

6.3.1 Anatomy of a Router >6.3.1.10 Packet Tracer- Exploring Internetworking Devices

Objectives

Part 1: Identify Physical Characteristics of Internetworking Devices
Part 2: Select Correct Modules for Connectivity
Part 3: Connect Devices

6.3.2 Router Boot-up >6.3.2.1 Cisco IOS

The figure on this page displays the words Operating Systems with the following words extending from the two main words:

  • Routing
  • Addressing
  • Interfaces
  • QoS
  • Security
  • Resource
  • Management

6.3.2 Router Boot-up >6.3.2.2 Bootset Files

The figure on this page shows how a router has Flash and NV RAM and RAM. This figure demonstrates that the IOS image, originally found in flash loads into RAM on boot up. It also demonstrates that the startup-config, originally found in NV RAM, loads into RAM on boot up to become the running-config.

6.3.2 Router Boot-up >6.3.2.3 Router Bootup Process

Figure 1 on this page shows the boot up process. First the router performs a P.O.S.T. and loads the bootstrap. Both are found in ROM. Secondly the router loads the I.O.S. found in flash or by T.F.T.P. Finally the router loads the startup configuration, found in N.V. Ram or by T.F.T.P. or console.

ROM POST Perform POST
ROM Bootstrap Load bootstrap
Flash Cisco Internetwork Operating System Locate and load operating system
TFTP server
NVRAM Configuration Locate and load configuration file or enter “setup mode”
TFTP server
Console

Figure 2 on this page highlights the POST section and shows the output directed to the console at CLI. A callout from the Bootstrap says, "Perform the POST and load the bootstrap program.".

Figure 3 on this page highlights the loading of the IOS and shows the output directed to the console at CLI. A callout from the Cisco Internetwork Operating System says, "Locate and load the Cisco IOS software.".

Figure 4 on this page highlights the loading of the startup configuration and shows the output directed to the console at CLI. A callout from the Configuration says, "Locate and load the startup configuration file or enter setup mode.".

6.3.2 Router Boot-up >6.3.2.4 Show Version Output

The figure on this page shows the output of the show version command at CLI and highlights the important sections as described in the page notes.

6.3.2 Router Boot-up >6.3.2.5 Video Demonstration – The Router Boot Process

The YouTube video on this page , titled " IOS Boot Process" demonstrates the boot up process on a Cisco router. It can be accessed via the following link:
https://www.youtube.com/watch?v=9BDsMuaifxM

6.3.2 Router Boot-up >6.3.2.6 Activity – The Router Boot Process

The interactive activity on this page allows the learner to match the description with the appropriate step in the boot up process.

The learner is asked to arrange each of the following Router Boot Process steps in the correct order:

Load the IOS (operating system file for the router – loaded into RAM after Bootstrap finds the IOS file to be used)
Perform POST (hardware check – performed by built-in ROM chip)
Load the Configuration File from FLASH (NVRAM), a TFTP Server OR Go into Setup Mode (to create a Configuration file)
Load Bootstrap (copied from ROM to RAM – locate the IOS)

6.4 Configuring a Cisco Router

6.4.1 configure Initial Settings >6.4.1.1 Router Configuration Steps

Figures 1 - 4 on this page shows a network with the CLI of a router.

Figure 1 shows the CLI and the commands to change the hostname of the router:

Router>enablw
Router#configure terminal
Enter configuration
commands, one per line.
End with CNTL/Z.
Router (config) #hostname R1
R1 (config) #

or

Router>en
Router#conf t
Enter configuration
commands, one per line.
End with CNTL/Z.
Router (config) #ho R2
R2 (config) #

Figure 2 shows the CLI and the commands to configure a secure password for privileged exec mode, the commands to configure standard options on the console and VTY lines as well as the command to encrypt all clear text passwords in the configuration file:

R1 (config) #enable secret class
R1 (config) #
R1 (config) #Line console 0
R1 (config-line) #password cisco
R1 (config-line) #login
R1 (config-line) #exit
R1 (config) #
R1 (config) #line v t y 0 4
R1 (config-line) #password cisco
R1 (config-line) #login
R1 (config-line) #exit
R1 (config) #
R1 (config) #service password-encryption
R1 (config) #

Figure 3 shows the CLI and the commands to configure a banner message:

R1 (config) #banner mtd #
Enter text message. End with the character '#'

WARNING: Unauthorised access is
prohibited!

#
R1 (config) #

Figure 4 shows the CLI and the commands to save the current running configuration to NV RAM:

R1 #copy running-config startup-config
Destination filename [startup-config]?
building configuration...
[OK]
R1 #

Figure 5 is an interactive activity allowing the learner to practice the basic configuration commands.

Enter the commands to configure the name of the router as 'R1'
Router> enable
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router (config) # hostname R1

Configure 'class' as the secret password.
R1 (config) # enable secret class
Configure 'cisco' as the console line password and require users to login.
Then exit line configuration mode.

R1 (config) # line console 0
R1 (config-line) # password cisco
R1 (config-line) # login
R1 (config-line) # exit

Configure 'cisco' as the VTY password for lines 0 through 4 and require
users to login.

R1 (config) # line v t y 0 4
R1 (config-line) # password cisco
R1 (config-line) # login

Exit line configuration mode and encrypt all clear text passwords.
R1 (config-line) # exit
R1 (config) # service password-encryption

Enter the banner 'Authorised Access Only' and use # as the delimiting character.
R1 (config) # banner motd #Authorised Access Only!#
Exit global configuration mode and save the configuration.
R1 (config) # exit
R1 # copy running-config startup-config
Destination filename [startup-config]?
Building configuration...
[OK]
R1 #

You successfully configured R1 with initial settings.

6.4.1 configure Initial Settings >6.4.1.2 Packet Tracer – Configure Initial Router Settings

Objectives

Part 1: Verify the Default Router Configuration
Part 2: Configure and Verify the Initial Router Configuration
Part 3: Save the Running Configuration File

6.4.2 Configure Interfaces >6.4.2.1 Configure LAN Interfaces

Figure 1 on this page shows a network with the CLI of a router. The CLI shows the commands to configure an ethernet interface with IP address, subnet mask and description. It also shows how to turn the interface on using the no shutdown command.

R1#conf t
Enter the configuration commands, one per line.
End with CNTL/Z.
R1 (config) #
R1 (config) #interface gigabitethernet 0/0
R1 (config-if) #ip address 192.168.10.1 255.255.255.0
R1 (config-if) #description Link to LAN-10
R1 (config-if) #no shutdown
%LINK-5-CHANGED: Interface GigabitEthernet0/0,
changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface
GigabitEthernet0/0, changed state to up
R1 (config-if) #exit
R1 (config) #
R1 (config) #int g0/1
R1 (config-if) #ip add 192.168.11.1 255.255.255.0
R1 (config-if) #des Link to LAN-11
R1 (config-if) #no shut
%LINK-5-CHANGED: Interface GigabitEthernet0/1,
changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface
GigabitEthernet0/1, changed state to up
R1 (config-if) #exit
R1 (config) #

Figure 2 on this page is an interactive activity allowing the learner to practice the basic interface configuration commands.

Configure the GigabitEthernet 0/0 interface with the IP address '192.168.10.1' and
subnet mask '255.255.255.0'. Describe the link as 'LAN-10' and activate the
interface.

R1 # configure terminal
Enter cionfiguration commands, one per line. End with CNTL/z.
R1 (config) # interface gigabitethernet 0/0
R1 (config-if) # ip address 192.168.10.1 255.255.255.0
R1 (config-if) # description LAN-10
R1 (config-if) # no shutdown
%LINK-5-CHANGED: Interface GigabitEthernet0/0, changed state to
up
%LINEPROTO-5-UPDOWN: Line protocol on Interface
GigabitEthernet0/0, changed state to up
R1 (config-if) #exit

Configure the GigabitEthernet 0/1 interface with IP address '192.168.11.1' and
subnet mask '255.255.255.0'. Describe the link as 'LAN-11' and activate the
interface.

R1 (config) # interface gigabitethernet 0/1
R1 (config-if) # ip address 192.168.11.1 255.255.255.0
R1 (config-if) # description LAN-11
R1 (config-if) # no shutdown
%LINK-5-CHANGED: Interface GigabitEthernet0/1, changed state to
up
%LINEPROTO-5-UPDOWN: Line protocol on Interface
GigabitEthernet0/1, changed state to up

You successfully configured the R1 LAN interfaces.

6.4.2 Configure Interfaces >6.4.2.2 Verify Interface Configuration

Figures 1 and 2 on this page show a network with the CLI of a router.

Figure 1 shows the results of the command show IP interface brief which shows the status of all interfaces on the router. It also shows the result of a ping command. Exclamation points are used to show successful pings:

R1#show IP interface brief
InterfaceIP-AddressOK?MethodStatus
GigabitEthernet0/0192.168.10.1YESmanualup
GigabitEthernet0/1192.168.11.1YESmanualup
Serial0/0/0209.165.200.225YESmanualup
Serial0/0/1unassignedYESNV RAMadministratively down
V lan1unassignedYESNV RAMadministratively down
R1#
R1#ping 209.165.200.226
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 209.165.200.226,
Timeout is 2 seconds:
! ! ! ! !
Succes rate is 100 percent (5/5),
Round-trip min\avg\max = 1\2\9 ms
R1#

Figure 2 shows the results of the command show IP route.

R1#show IP route
Codes: L – local, C – connected, S- static, R – RIP,

M – mobile, B – BGP,
D – EIGRP, EX – EIGRP external, O – OSPF,
IA – OSPF inter area,
N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2,
E1 – OSPF external type 1,E2 – OSPF external type 2, E - EGP,I – IS-IS, L1 – IS-IS level-1,
L2 – IS-IS level-2, ia – IS-IS inter area
* – candidate default, U – per-user static route, O – ODR
P – periodic downloaded static route

Gateway of last resort is not set

192.168.10.0/24 is variably subnetted, 2 subnets, 3 masks
C 192.168.10.0/24 is directly connected, GigabitEthernet 0/0
L 192.168.10.0/32 is directly connected, GigabitEthernet 0/0
192.168.11.0/24 is variably subnetted, 2 subnets, 3 masks
C 192.168.11.0/24 is directly connected, GigabitEthernet 0/1
L 192.168.11.1/32 is directly connected, GigabitEthernet 0/1
209.165.200.0/24 is variably subnetted, 2 subnets, 3 masks
C 209.165.200.224/30 is directly connected, Serial0/0/0
L 209.165.200.224/30 is directly connected, Serial0/0/0
R1#

6.4.3 Configuring the Default Gateway >6.4.3.1 Default gateway on a Host

Figures 1 and 2 on this page show a router with two LANs. Each LAN has 2 PC's as follows:

PC'sNetworkRouter Interface
1 and 2192.168.10.0/24G0/0
3 and 4192.168.11.0/24G0/1

Figure 1 shows how a host can communicate with another host on the same LAN without the use of the gateway as described in the page notes.

Figure 2 shows how a host requires the gateway to communicate with a host on another LAN as described in the page notes.

6.4.3 Configuring the Default Gateway >6.4.3.2 Default Gateway on a switch

Figure 1 on this page shows a network with a worker connected to a LAN. The figure demonstrates how to configure a switch with a management interface (v. LAN 1) and a default gateway so a network administrator can manage the switch remotely. Without these configured, you cannot connect to a switch remotely.

The network consists of:

  • PC1 and PC2 connected to switch S1 with IP address 192.168.10.0/24.
  • S1 is connected to interface G0/0 on router R1.
  • PC3 is connected to switch S2 with IP address 192.168.11.0/24.
  • S2 is connected to interface G0/1 on router R1.

The console window shows:

S1 #show running-config
Building configuration...
!
<output omitted>
service password-encryption
!
hostname S1
!
Interface Vlan1

IP address 192.168.10.50
!
IP default-gateway 192.168.10.1
<output omitted
>

The description given for this figure is "If the default gateway were not configured on S1, response packets from S1 would not be able to reach the administrator at 192.168.11.10. The administrator would not be able to manage the device remotely. "

Figure 2 on this page is an interactive activity allowing the learner to practice configuring a management interface and default gateway on a switch.

Enter global configuration and configure '192.168.10.1' as the default
gateway for S1.

S1# configure terminal
Enter configuration commands, one per line. End with
CNTL/Z.
S1 (config) # IP default-gateway 192.168.10.1
S1 (config) #

You successfully configured the default gateway on S1

6.4.3 Configuring the Default Gateway >6.4.3.3 Packet Tracer – Connect a Router to a LAN

Objectives

Part 1: Display Router Information
Part 2: Configure Router Interfaces
Part 3: Verify the Configuration

6.4.3 Configuring the Default Gateway >6.4.3.4 Packet Tracer – Troubleshooting Default Gateway Issues

Objectives

Part 1: Verify Network Documentation and Isolate Problems
Part 2: Implement, Verify, and Document Solutions

6.4.3 Configuring the Default Gateway >6.4.3.5 Lab – Initializing and Reloading a router and Swicth

See Lab Descriptions.

6.5 Summary

6.5.1 Summary >6.5.1.1 Class Activity - Can You Read this Map

Objectives

Explain how network devices use routing tables to direct packets to a destination network.
In this activity, given a scenario, you will determine whether high-reliability messaging should be used. You will focus on whether the final message is complete, correct, and delivered in a timely manner.

6.5.1 Summary >6.5.1.2 Packet Tracer

Objectives

  • Finish the network documentation
  • Perform basic device configurations on a router and a switch
  • Verify connectivity and troubleshoot any issues

6.5.1 Summary >6.5.1.3 Summary

The figure on this page shows a network with two routers connected by a serial link. Each router has 2 LANs. There is a callout showing that router 1 has 3 directly connected networks and 2 remote networks in its routing table.

R1 has three directly connected networks:

  • S1; IP address 192.138.10.0/24
  • S2; IP address 192.138.11.0/24
  • R2; IP address 209.165.200.224/30

R1 also has two remote networks that it can learn about from R2:

  • S3; IP address 10.1.1.0/24
  • S4; IP address 10.1.2.0/24

End of Chapter 6: Network Layer.

Next - Chapter 7: Transport Layer.

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Page last modified on October 09, 2014, at 02:07 AM