Router
Router
A router is a network device that connects different networks together and forwards data between them using IP addresses.
The most common job of a router is connecting your local network (LAN) to the Internet (WAN).
Example
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PC
|
Switch
|
Router
|
Internet
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When your computer wants to access a website:
Your PC sends packets to the router.
The router examines the destination IP address.
The router determines the best path.
The router forwards the packet to the Internet.
What Does a Router Do?
Routing
Determines the best path for network traffic.
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192.168.1.10 → Google
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The router decides where the packet should go next.
Default Gateway
In most networks, the router is the default gateway.
Example:
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IP Address: 192.168.1.100
Gateway: 192.168.1.1
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If a device wants to reach another network, it sends traffic to the gateway (router).
NAT (Network Address Translation)
Converts private IP addresses into public IP addresses.
Example:
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Private IP:
192.168.1.100
Public IP:
73.24.100.15
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This allows many devices to share one public Internet address.
DHCP
Many routers automatically assign:
IP address
Subnet mask
Gateway
DNS server
to devices on the network.
Router in the OSI Model
A router primarily operates at:
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Layer 3 (Network Layer)
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It makes forwarding decisions using:
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IP Addresses
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Home Router
A typical home router combines:
Router
Switch
Wireless Access Point
Firewall
into one device.
Example:
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Cable Modem
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Home Router
/ \
PC Wi-Fi
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Common brands:
Netgear
Linksys
ASUS
TP-Link
What is an Enterprise Router?
An Enterprise Router is a high-performance router used in businesses, data centers, schools, hospitals, and large organizations.
Enterprise routers support:
Thousands of users
Multiple Internet connections
VPNs
Advanced security
Dynamic routing protocols
Enterprise Router Example
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Branch Office
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Enterprise Router
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Corporate WAN
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Data Center
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Unlike a home router, enterprise routers are designed for:
High availability
Redundancy
Scalability
Performance
Enterprise Router Features
Dynamic Routing
Automatically learns network routes using protocols such as:
OSPF
EIGRP
BGP
RIP
VPN Support
Allows secure remote access.
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Employee Laptop
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VPN
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Enterprise Router
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Redundancy
Can connect to multiple Internet Service Providers.
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ISP #1
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Router
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ISP #2
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If one connection fails, traffic automatically uses another.
Access Control Lists (ACLs)
Allows network administrators to permit or deny traffic.
Example:
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Allow:
10.1.1.0/24
Block:
172.16.0.0/16
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What is a Cisco Router?
A Cisco Router is simply a router manufactured by Cisco Systems, one of the world's largest networking companies.
Cisco routers are widely used in:
Enterprises
Data centers
Government agencies
Universities
Internet Service Providers (ISPs)
Cisco IOS
Cisco routers run an operating system called:
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Cisco IOS
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(Internetwork Operating System)
Administrators configure Cisco routers using commands.
Example:
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Router> enable
Router# configure terminal
Router(config)# interface gigabitEthernet0/0
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Cisco Router Example
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PCs
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Switch
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Cisco Router
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Internet
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The Cisco router handles:
Routing
NAT
VPNs
ACLs
DHCP
Security
Common Cisco Router Models
Branch Offices
Cisco ISR 1000 Series
Cisco ISR 4000 Series
Large Enterprises
Cisco ASR Series
Service Providers
Cisco ASR 9000
Cisco Carrier Routing Systems
Switch vs Router
Feature Switch RouterOSI Layer Layer 2 Layer 3
Uses MAC Addresses Yes No
Uses IP Addresses No Yes
Connects Devices Yes Yes
Connects Different Networks No Yes
Default Gateway No Yes
Network+ Exam Tips
Layer 2 Switch
Uses MAC addresses
Forwards frames
Connects devices on the same LAN
Router
Uses IP addresses
Forwards packets
Connects different networks
Enterprise Router
Large-scale business router
Supports OSPF, EIGRP, BGP
VPNs and redundancy
Cisco Router
Router made by Cisco
Runs Cisco IOS
Most common enterprise networking platform
Quick Memory Trick
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Switch = MAC Address
Router = IP Address
Enterprise Router = Business-Grade Router
Cisco Router = Industry Standard Enterprise Router
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Simple definition: A router is a Layer 3 networking device that uses IP addresses to connect different networks and forward packets between them. An enterprise router is a high-performance business router with advanced routing and security features, while a Cisco router is a router manufactured by Cisco Systems and is widely used in enterprise and service-provider networks.
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