CCNA 2 v6.0 Study Material – Chapter 1: Routing Concepts

Chapter 1 – Sections & Objectives

  • 1.1 Router Initial Configuration
    • Describe the primary functions and features of a router.
    • Configure basic settings on a router to route between two directly-connected networks, using CLI.
    • Verify connectivity between two networks that are directly connected to a router.
  • 1.2 Routing Decisions
    • Explain the encapsulation and de-encapsulation process used by routers when switching packets between interfaces.
    • Explain the path determination function of a router.
  • 1.3 Router Operation
    • Explain routing table entries for directly connected networks.
    • Explain how a router builds a routing table of directly connected networks.
    • Explain how a router builds a routing table using static routes.
    • Explain how a router builds a routing table using a dynamic routing protocol.

1.1 Router Initial Configuration

1.1.1 Router Functions

Characteristics of a Network

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Why Routing?

The router is responsible for the routing of traffic between networks.

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Routers are Computers

Routers are specialized computers containing the following required components to operate:

  • Central processing unit (CPU)
  • Operating system (OS) – Routers use Cisco IOS
  • Memory and storage (RAM, ROM, NVRAM, Flash, hard drive)

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Routers use specialized ports and network interface cards to interconnect to other networks.

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Router Memory

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Routers Interconnect Networks

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Routers Choose Best Paths

  • Routers use static routes and dynamic routing protocols to learn about remote networks and build their routing tables.
  • Routers use routing tables to determine the best path to send packets.
  • Routers encapsulate the packet and forward it to the interface indicated in routing table.

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Packet Forwarding Methods

  • Process switching – An older packet forwarding mechanism still available for Cisco routers.
  • Fast switching – A common packet forwarding mechanism which uses a fast-switching cache to store next hop information.
  • Cisco Express Forwarding (CEF) – The most recent, fastest, and preferred Cisco IOS packet-forwarding mechanism.

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1.1.2 Connect Devices

Connect to a Network

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Default Gateways

To enable network access devices, must be configured with the following IP address information:

  • IP address– Identifies a unique host on a local network.
  • Subnet mask – Identifies the host’s network subnet.
  • Default gateway – Identifies the router a packet is sent to when the destination is not on the same local network subnet.

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Document Network Addressing

Network documentation should include at least the following in a topology diagram and addressing table:

  • Device names
  • Interfaces
  • IP addresses and subnet masks
  • Default gateways

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Enable IP on a Host

Statically Assigned IP address – The host is manually assigned an IP address, subnet mask and default gateway. A DNS server IP address can also  be assigned.

  • Used to identify specific network resources such as network servers and printers.
  • Can be used in very small networks with few hosts.

Dynamically Assigned IP Address – IP Address information is dynamically assigned by a server using Dynamic Host Configuration Protocol (DHCP).

  • Most hosts acquire their IP address information through DHCP.
  • DHCP services can be provided by Cisco routers.

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Device LEDs

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Console Access

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Enable IP on a Switch

  • Network infrastructure devices require IP addresses to enable remote management.
  • On a switch, the management IP address is assigned on a virtual interface called a switched virtual interface (SVI)

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1.1.3 Router Basic Settings

Configure Router Basic Settings

  • Name the device –Distinguishes it from other routers
  • Secure management access – Secures privileged EXEC, user EXEC, and Telnet access, and encrypts passwords .
  • Configure a banner –Provides legal notification of unauthorized access.
  • Save the Configuration

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Configure an IPv4 Router Interface

To be available, a router interface  must be:

  • Configured with an address and subnet mask.
  • Activated using no shutdown command. By default LAN and WAN interfaces are not activated.
  • Configured with the clock rate command on the Serial cable end labeled DCE.

Optional description can be included.

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Configure an IPv6 Router Interface

Configure interface with IPv6 address and subnet mask:

  • Use the ipv6 addressipv6-address/ipv6-length [link-local | eui-64]interface configuration command.
  • Activate using the no shutdown command.

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IPv6 interfaces can support more than one address:

  • Configure a specified global unicast – ipv6address ipv6-address/ipv6-length
  • Configure a global IPv6 address with an interface identifier (ID) in the low-order 64 bits  – ipv6address ipv6-address/ipv6-length eui-64
  • Configure a link-local address – ipv6address ipv6-address/ipv6-length link-local

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Configure an IPv4 Loopback Interface

A loopback interface is a logical interface that is internal to the router:

  • It is not assigned to a physical port, it is considered a software interface that is automatically in an UP state.
  • A loopback interface is useful for testing.
  • It is important in the OSPF routing process.

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1..1.4 Verify Connectivity of Directly Connected Networks

Verify Interface Settings

Show commands are used  to verify operation and configuration of interface:

  • show ip interfaces brief
  • show ip route
  • show running-config

Show commands that are used to gather more detailed interface information:

  • show interfaces
  • show ip interfaces

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Verify IPv6 Interface Settings

Common commands to verify the IPv6 interface configuration:

  • show ipv6 interface brief – displays a summary for each of the interfaces.
  • show ipv6 interface gigabitethernet 0/0 – displays the interface status and all the IPv6 addresses for this interface.
  • show ipv6 route – verifies that IPv6 networks and specific IPv6 interface addresses have been installed in the IPv6 routing table.

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Filter Show Command Output

Show command output can be managed using the following command and filters:

  • Use theterminal length number command to specify the number of lines to be displayed.
  • To filter specific output of commands use the (|)pipe character after show command. Parameters that can be used after pipe include:
  • section, include, exclude,  begin

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Command History Feature

The command history feature temporarily stores a list of executed commands for access:

  • To recall commands press Ctrl+P or the UP Arrow.
  • To return to more recent commands press Ctrl+N or the Down Arrow.
  • By default, command history is enabled and the system captures the last 10 commands in the buffer. Use the show history privileged EXEC command to display the buffer contents.
  • Use the terminal history size user EXEC command to increase or decrease size of the buffer.

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1.2 Routing Decisions

1.2.1 Switching Packets Between Networks

Router Switching Function

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Send a Packet

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Forward to Next Hop

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Packet Routing

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Reach the Destination

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1.2.2 Path Determination

Routing Decisions

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Best Path

  • Best path is selected by a routing protocol based on the value or metric it uses to determine the distance to reach a network:
    • A metric is the value used to measure the distance to a given network.
    • Best path to a network is the path with the lowest metric.
  • Dynamic routing protocols use their own rules and metrics to build and update routing tables:
    • Routing Information Protocol (RIP) – Hop count
    • Open Shortest Path First (OSPF) – Cost based on cumulative bandwidth from source to destination
    • Enhanced Interior Gateway Routing Protocol (EIGRP) – Bandwidth, delay, load, reliability

Load Balancing

  • When a router has two or more paths to a destination with equal cost metrics, then the router forwards the packets using both paths equally:
    • Equal cost load balancing can improve network performance.
    • Equal cost load balancing can be configured to use both dynamic routing protocols and static routes.

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Administrative Distance

  • If multiple paths to a destination are configured on a router, the path installed in the routing table is the one with the lowest Administrative Distance (AD):
    • A static route with an AD of 1 is more reliable than an EIGRP-discovered route with an AD of 90.
    • A directly connected route with an AD of 0 is more reliable than a static route with an AD of 1.

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1.3 Router Operation

1.3.1 Analyze the Routing Table

The Routing Table

  • A routing table is a file stored in RAM that contains information about:
    • Directly connected routes
    • Remote routes

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Routing Table Sources

The show ip route command is used to display the contents of the routing table:

  • Local route interfaces – Added to the routing table when an interface is configured. (displayed in IOS 15 or newer for IPv4 routes and all IOS releases for IPv6 routes.)
  • Directly connected interfaces – Added to the routing table when an interface is configured and active.
  • Static routes – Added when a route is manually configured and the exit interface is active.
  • Dynamic routing protocol – Added when EIGRP or OSPF are implemented and networks are identified.

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Remote Network Routing Entries

Interpreting the entries in the routing table

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1.3.2 Directly Connected Routes

Directly Connected Interfaces

A newly deployed router, without any configured interfaces, has an empty routing table.

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Directly Connected Routing Table Entries

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Directly Connected Example

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Directly Connected IPv6 Example

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13.3 Statically Learned Routes

Static Routes

Static routes and default static routes can be implemented after directly connected interfaces are added to the routing table:

  • Static routes are manually configured.
  • They define an explicit path between two networking devices.
  • Static routes must be manually updated if the topology changes.
  • Their benefits include improved security and control of resources.
  • Configure a static route to a specific network using the ip route network mask {next-hop-ip | exit-intf} command.
  • A default static route is used when the routing table does not contain a path for a destination network.
  • Configure a default static route using the ip route 0.0.0.0 0.0.0.0 {exit-intf | next-hop-ip} command.

Static Route Example

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Entering and Verifying a Static Route

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Static IPv6 Route Examples

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1.3.4 Dynamic Routing Protocols

Dynamic Routing

  • Dynamic routing is used by routers to share information about the reachability and status of remote networks.
  • It performs network discovery and maintains routing tables.
  • Routers have converged after they have finished exchanging and updating their routing tables.

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IPv4 Routing Protocols

Cisco routers can support a variety of dynamic IPv4 routing protocols including:

  • EIGRP –Enhanced Interior Gateway Routing Protocol
  • OSPF –Open Shortest Path First
  • IS-IS –Intermediate System-to-Intermediate System
  • RIP –Routing Information Protocol

Use the router ? Command in global configuration mode to determine which routing protocols are supported by the IOS.

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IPv4 Dynamic Routing Examples

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IPv6 Routing Protocols

  • Cisco routers can support a variety of dynamic IPv6 routing protocols including:
    • RIPng  (RIP next generation)
    • OSPFv3
    • EIGRP for IPv6
  • Use the ipv6 router ? command to determine which routing protocols are supported by the IOS

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IPv6 Dynamic Routing Examples

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1.4 Chapter Summary

Describe the primary functions and features of a router.

Configure basic settings on a router to route between two directly-connected networks, using CLI.

Verify connectivity between two networks that are directly connected to a router.

Explain how routers use information in data packets to make forwarding decisions in a small to medium-sized business network.

Explain the encapsulation and de-encapsulation process used by routers when switching packets between interfaces.

Explain the path determination function of a router.

Explain how a router learns about remote networks when operating in a small to medium-sized business network.

Explain how a router builds a routing table of directly connected networks.

Explain how a router builds a routing table using static routes.

Explain how a router builds a routing table using a dynamic routing protocol.

Section 1.1

New Terms and Commands

  • Topology
  • Speed
  • Cost
  • Security
  • Availability
  • Scalability
  • Reliability
  • Point-to-Point Protocol (PPP)
  • Process Switching
  • Fast switching
  • Cisco Express Forwarding (CEF)
  • Wireless access points (WAPs)
  • Edge router
  • Gateway of Last Resort
  • Topology diagram
  • Secure Shell (SSH)
  • Hypertext Transfer Protocol Secure (HTTPS)
  • Console cable
  • Terminal emulation software –  Tera Term, PuTTY, HyperTerminal
  • Secure management access
  • Ipv6 address ipv6-address/ipv6-length [link-local | eui-64] interface configuration command.
  • no shutdown command
  • loopback interface
  • interface loopback number  command
  • show ip route command
  • show running-config interfaceinterface-id
  • show ip interface brief command
  • show running-config interface command
  • show ip interfaces command
  • Show ipv6 interface commandshow interfaces command
  • show ipv6 interface brief command
  • show ipv6 route command
  • pipe (|) character
  • Ctrl+P
  • Ctrl+N
  • show history
  • terminal history

Section 1.2

New Terms and Commands

  • Metrics
  • Routing Information Protocol (RIP)
  • Open Shortest Path First (OSPF)
  • Enhanced Interior Gateway Routing Protocol (EIGRP)
  • load balancing
  • IS-IS – Intermediate System-to-Intermediate System
  • RIPng (RIP next generation)
  • OSPFv3

Section 1.3

New Terms and Commands

  • Administrative Distance (AD)
  • Local Route interfaces
  • Static routes
  • Route timestamp
  • Route source
  • ip route network mask { next-hop-ip | exit-intf }
  • ip route 0.0.0.0 0.0.0.0 { exit-intf | next-hop-ip }
  • ipv6 unicast-routing
  • ipv6 route ::/0 {ipv6-address | interface-type interface-number}
  • ipv6 route ipv6-prefix/prefix-length {ipv6-address|interface-type interface-number}
  • Router ? command
  • Ipv6 router ? command

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