Module 10: Basic Router Configuration

10.1 Configure Initial Router Settings

  • Basic Router Configuration Steps:

    • Configure the device name using the hostname hostname command in global configuration mode.

    • Secure privileged EXEC mode using the enable secret password command in global configuration mode. This sets an encrypted password for accessing privileged mode.

    • Secure user EXEC mode by configuring a password on the console line. This involves the following commands:

      • line console 0 to enter line configuration mode for the console.

      • password password to set the password.

      • login to require a password for console access.

    • Secure remote Telnet/SSH access by configuring a password on the VTY (Virtual Terminal) lines:

      • line vty 0 4 to enter line configuration mode for VTY lines 0 through 4.

      • password password to set the password.

      • login to require a password for VTY access.

      • transport input {ssh | telnet} to specify the allowed transport protocols (SSH or Telnet).

    • Encrypt all plaintext passwords using the service password-encryption command in global configuration mode. This encrypts all passwords in the configuration file.

    • Provide a legal notification banner using the banner motd # message # command in global configuration mode. Replace message with the banner text, delimited by the # character. This displays a message to users before they log in.

    • Save the configuration using the copy running-config startup-config command in privileged EXEC mode. This saves the current running configuration to NVRAM (Non-Volatile RAM) so it is retained after a reboot.

  • Basic Router Configuration Example:

    • Commands for basic router configuration on R1:

      • R1(config)# hostname R1 - Sets the hostname of the router to R1.

      • R1(config)# enable secret class - Sets the encrypted password for privileged EXEC mode to "class".

      • R1(config)# line console 0

      • R1(config-line)# password cisco - Sets the console password to "cisco".

      • R1(config-line)# login - Requires a password for console access.

      • R1(config-line)# line vty 0 4

      • R1(config-line)# password cisco - Sets the VTY password to "cisco".

      • R1(config-line)# login - Requires a password for VTY access.

      • R1(config-line)# transport input ssh telnet - Specifies that only SSH and Telnet are allowed for VTY access.

      • R1(config-line)# exit - Exits line configuration mode.

      • R1(config)# service password-encryption - Enables password encryption.

      • `R1(config)# banner motd # Enter TEXT message. End with a new line and the #

WARNING: Unauthorized access is prohibited!
****- Sets the Message of the Day (MOTD) banner. *R1(config)# exit- Exits global configuration mode. *R1# copy running-config startup-config` - Saves the configuration to NVRAM.

10.2 Configure Interfaces

  • Configuring Router Interfaces:

    • To configure a router interface, use the following commands:

      • Router(config)# interface type-and-number - Specifies the interface to configure (e.g., interface GigabitEthernet0/0/0).

      • Router(config-if)# description description-text - Adds a description to the interface for documentation purposes.

      • Router(config-if)# ip address ipv4-address subnet-mask - Configures the IPv4 address and subnet mask for the interface.

      • Router(config-if)# ipv6 address ipv6-address/prefix-length - Configures the IPv6 address and prefix length for the interface.

      • Router(config-if)# no shutdown - Activates the interface.

    • It's a good practice to use the description command to add information about the network connected to the interface.

    • The no shutdown command activates the interface.

  • Configure Router Interfaces Example:

    • The commands to configure interface G0/0/0 on R1 are:

      • R1(config)# interface gigabitEthernet 0/0/0

      • R1(config-if)# description Link to LAN

      • R1(config-if)# ip address 192.168.10.1 255.255.255.0

      • R1(config-if)# ipv6 address 2001:db8:acad:10::1/64

      • R1(config-if)# no shutdown

      • R1(config-if)# exit

    • The commands to configure interface G0/0/1 on R1 are:

      • R1(config)# interface gigabitEthernet 0/0/1

      • R1(config-if)# description Link to R2

      • R1(config-if)# ip address 209.165.200.225 255.255.255.252

      • R1(config-if)# ipv6 address 2001:db8:feed:224::1/64

      • R1(config-if)# no shutdown

      • R1(config-if)# exit

  • Verify Interface Configuration:

    • To verify interface configuration, use the show ip interface brief and show ipv6 interface brief commands.

      • show ip interface brief - Displays all interfaces, their IP addresses, and their current status.

      • show ipv6 interface brief - Displays all interfaces, their IPv6 addresses, and their current status.

  • Configure Verification Commands:

    • The table summarizes show commands used to verify interface configuration.

      • show ip interface brief - Displays all interfaces, their IP addresses, and their current status.

      • show ipv6 interface brief - Displays all interfaces, their IPv6 addresses, and their current status.

      • show ip route - Displays the contents of the IPv4 routing table stored in RAM.

      • show ipv6 route - Displays the contents of the IPv6 routing table stored in RAM.

      • show interfaces - Displays statistics for all interfaces on the device. Only displays the IPv4 addressing information.

      • show ip interfaces - Displays the IPv4 statistics for all interfaces on a router.

      • show ipv6 interfaces - Displays the IPv6 statistics for all interfaces on a router.

    • Examples:

      • R1# show ip interface brief

      • R1# show ipv6 interface brief

      • R1# show ip route

      • R1# show ipv6 route

      • R1# show interfaces gig0/0/0

      • R1# show ip interface g0/0/0

      • R1# show ipv6 interface g0/0/0

10.3 Configure the Default Gateway

  • Default Gateway on a Host:

    • The default gateway is used when a host sends a packet to a device on another network.

    • The default gateway address is generally the router interface address attached to the local network of the host.

    • To reach PC3, PC1 addresses a packet with the IPv4 address of PC3, but forwards the packet to its default gateway, the G0/0/0 interface of R1.

    • Note: The IP address of the host and the router interface must be in the same network.

  • Default Gateway on a Switch:

    • A switch must have a default gateway address configured to remotely manage the switch from another network.

    • To configure an IPv4 default gateway on a switch, use the ip default-gateway ip-address global configuration command.