Router Configuration

Objective

Configure a Cisco router with interfaces, static routes, and router-on-a-stick for inter-VLAN routing.

Tools & Technologies

Cisco IOS
static routes
inter-VLAN routing
router-on-a-stick

Key Commands

ip address 192.168.1.1 255.255.255.0

ip route 10.0.0.0 255.0.0.0 192.168.1.2

interface Gi0/0.10

encapsulation dot1Q 10

Architecture Overview

graph LR subgraph Router G0[Gi0/0\n192.168.1.1/24] G1[Gi0/1\n10.0.0.1/24] G0V10[Gi0/0.10\n10.10.0.1/24] G0V20[Gi0/0.20\n10.20.0.1/24] end G0 <--> SW1[Switch/LAN] G1 <--> SW2[WAN/ISP] G0V10 -.->|VLAN10| SW1 G0V20 -.->|VLAN20| SW1 style Router fill:#1a1a2e,stroke:#00d4ff

Step-by-Step Process

Configure Physical Interfaces

Assign IP addresses to interfaces and bring them up.

Router(config)# interface GigabitEthernet0/0
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)# no shutdown
Router(config-if)# description LAN_INTERFACE

Router# show interfaces GigabitEthernet0/0
Router# show ip interface brief

Static Routes

Configure static routes to reach networks beyond directly connected interfaces.

! Route to 10.0.0.0/8 via 192.168.1.2
ip route 10.0.0.0 255.0.0.0 192.168.1.2
! Default route
ip route 0.0.0.0 0.0.0.0 192.168.1.254

show ip route
show ip route static

Router-on-a-Stick (Inter-VLAN)

Use subinterfaces on a single trunk link to route between VLANs.

interface Gi0/0.10
 encapsulation dot1Q 10
 ip address 10.10.0.1 255.255.255.0
 description VLAN10_HR

interface Gi0/0.20
 encapsulation dot1Q 20
 ip address 10.20.0.1 255.255.255.0
 description VLAN20_ENG

! Hosts set default gateway to subinterface IP

Challenges & Solutions

Interface stays down without no shutdown
Default route (0.0.0.0/0) via unreachable gateway causes black hole

Key Takeaways

Router-on-a-stick creates a single point of failure — L3 switch is better for production
show ip route shows routing table with codes: C=connected, S=static, R=RIP