Configure Initial Router Settings
Basic Router Configuration Steps
- Configure the device name.
Router(config)# hostname hostname - Secure privileged EXEC mode.
Router(config)# enable secret password - Secure user EXEC mode.
Router(config)# line console 0 Router(config-line)# password password Router(config-line)# login - Secure remote Telnet / SSH access.
Router(config-line)# line vty 0 4 Router(config-line)# password password Router(config-line)# login Router(config-line)# transport input {ssh | telnet} - Secure all passwords in the config file.
Router(config-line)# exit Router(config)# service password-encryption - Provide legal notification.
Router(config)# banner motd delimiter message delimiter - Save the configuration.
Router(config)# end Router# copy running-config startup-config
Basic Router Configuration Example
To configure the device name for R1, use the following commands.
Router> enable
Router# configure terminal
Enter configuration commands, one per line.
End with CNTL/Z.
Router(config)# hostname R1
R1(config)#
The following commands secure privileged EXEC mode and user EXEC mode, enable Telnet and SSH remote access, and encrypt all plaintext (i.e., user EXEC and VTY line) passwords.
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 vty 0 4
R1(config-line)# password cisco
R1(config-line)# login
R1(config-line)# transport input ssh telnet
R1(config-line)# exit
R1(config)#
R1(config)# service password-encryption
R1(config)#
Configure Interfaces
Configure Router Interfaces
the Cisco ISR 4321 router is equipped with two Gigabit Ethernet interfaces:
- GigabitEthernet 0/0/0 (G0/0/0)
- GigabitEthernet 0/0/1 (G0/0/1)
The task to configure a router interface is very similar to a management SVI on a switch. Specifically, it includes issuing the following commands:
Router(config)# interface type-and-number
Router(config-if)# description description-text
Router(config-if)# ip address ipv4-address subnet-mask
Router(config-if)# ipv6 address ipv6-address/prefix-length
Router(config-if)# no shutdown
Although the description command is not required to enable an interface, it is good practice to use it. It can be helpful in troubleshooting on production networks by providing information about the type of network connected. For example, if the interface connects to an ISP or service carrier, the description command would be helpful to enter the third-party connection and contact information.
Note: The description-text is limited to 240 characters.
Using the no shutdown command activates the interface and is similar to powering on the interface.
Configure Router Interfaces Example
To configure the the interfaces on R1, use the following commands.
R1> enable
R1# configure terminal
Enter configuration commands, one per line.
End with CNTL/Z.
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
R1(config)#
*Aug 1 01:43:53.435: %LINK-3-UPDOWN: Interface GigabitEthernet0/0/0, changed state to down
*Aug 1 01:43:56.447: %LINK-3-UPDOWN: Interface GigabitEthernet0/0/0, changed state to up
*Aug 1 01:43:57.447: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0/0, changed state to up
R1(config)#
R1(config)#
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
R1(config)#
*Aug 1 01:46:29.170: %LINK-3-UPDOWN: Interface GigabitEthernet0/0/1, changed state to down
*Aug 1 01:46:32.171: %LINK-3-UPDOWN: Interface GigabitEthernet0/0/1, changed state to up
*Aug 1 01:46:33.171: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0/1, changed state to up
R1(config)#
Note: Notice the informational messages informing us that G0/0/0 and G0/0/1 are enabled.
Verify Interface Configuration
The most useful of these is the show ip interface brief and show ipv6 interface brief commands
R1# show ip interface brief
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0/0 192.168.10.1 YES manual up up
GigabitEthernet0/0/1 209.165.200.225 YES manual up up
Vlan1 unassigned YES unset administratively down down
R1# show ipv6 interface brief
GigabitEthernet0/0/0 [up/up]
FE80::201:C9FF:FE89:4501
2001:DB8:ACAD:10::1
GigabitEthernet0/0/1 [up/up]
FE80::201:C9FF:FE89:4502
2001:DB8:FEED:224::1
Vlan1 [administratively down/down]
unassigned
R1#
Configuration Verification Commands
The table summarizes the more popular show commands used to verify interface configuration.
| Commands | Description |
|---|---|
| show ip interface brief | The output displays all interfaces, their IP addresses, and their current status. The configured and connected interfaces should display a Status of “up” and Protocol of “up”. Anything else would indicate a problem with either the configuration or the cabling. |
| show ipv6 interface brief | Displays the contents of the IP routing tables stored in RAM. |
| show ip route | Displays the IPv4 statistics for all interfaces on a router. |
| show ipv6 route | Displays the IPv6 statistics for all interfaces on a router. |
| show interfaces | Displays statistics for all interfaces on the device. However, this command will only display the IPv4 addressing information. |
| show ip interface | Displays the IPv4 statistics for all interfaces on a router. |
| show ipv6 interface | Displays the IPv6 statistics for all interfaces on a router. |
Configure the Default Gateway
Default Gateway on a Host
If your local network has only one router, it will be the gateway router and all hosts and switches on your network must be configured with this information. If your local network has multiple routers, you must select one of them to be the default gateway router.
The default gateway is only used when the host wants to send a packet to a device on another network.
Default Gateway on a Switch
A switch that interconnects client computers is typically a Layer 2 device. As such, a Layer 2 switch does not require an IP address to function properly. However, an IP configuration can be configured on a switch to give an administrator remote access to the switch.
To configure an IPv4 default gateway on a switch, use the ip default-gateway ip-address global configuration command. The ip-address that is configured is the IPv4 address of the local router interface connected to the switch.
Switch(config)# interface vlan 1
Switch(config-if)# ip address ipaddress subnetmask
Switch(config-if)# ip default-gateway ip-address
Switch(config-if)# no shutdown
Note: Packets originating from host computers connected to the switch must already have the default gateway address configured on their host computer operating systems.
A workgroup switch can also be configured with an IPv6 address on an SVI. However, the switch does not require the IPv6 address of the default gateway to be configured manually. The switch will automatically receive its default gateway from the ICMPv6 Router Advertisement message from the router.