What is a Router?

• A special purpose computer• Hardware and software dedicated to path

selection and packet switching• Cisco routers derived from Unix computers

Router Capabilities

• Main Functions– Path selection– Packet switching

• Additional Functions– Broadcast containment– VLAN links– Security / Access control

Router Roles

• Network Edge– WAN links to other sites in the enterprise– WAN gateway to Internet

• Network Core– Backbone links– Collapsed backbone

• Anywhere– Network segmentation device– Security device

Router Roles

• WAN links to other sites in the enterprise– Example: connect Chabot to Las Positas– Use serial ports– Low bandwidth, compared to LAN (T-1 is 1.54

mbs)– Cisco 2500 series router used frequently for this

role.

Router Roles

• WAN Gateway to Internet– Example: connects CLPCCD network to ISP– Uses serial port– Low bandwidth, compared to LAN (T-1 is 1.54

mbs)– Cisco 2500 series router used frequently for this

role

Router Roles

• Backbone links– Connect user groups to backbone– Use ethernet ports (or other LAN ports such as

token ring or FDDI)– High bandwidth, (Typically 10 or 100 mbs)– An older network design– Cisco modular routers used frequently for this

role (e.g. 3600, 4000 series), but can be done with 2514 in low traffic situations

Router Roles

• “Collapsed Backbone”– Backbone in a box; center of extended star– Uses ethernet ports or fast ethernet ports– A modern network design– Uses high-end Cisco routers (e.g.7500 series)– Router often works with large switches to manage

VLANS.

Router Roles

• Network segmentation device– Router links:

• networks• subnets• switch VLANS

– Broadcasts (usually) not forwarded– Router works together with high-end switch (ISL)

or router module is part of the switch

Router Roles

• Security device– Access control rules allow router to control traffic

between:• networks• subnets• switch VLANS

– Traffic regulated by “Access Control Lists”

Router Roles

• The Cisco 7507 at the core of Chabot’s net performs all these roles:– WAN links to other sites in the enterprise– Collapsed backbone– Network segmentation device (VLAN links,

broadcast containment)– Security device

What is this router’s role?

Gateway to Internet

What is this router’s role?

WAN link to a remote site in the company

San FranciscoNetwork

San JoseNetwork

What is this router’s role?

Backbone access

Science Dept

EngineeringDept

BusinessDept

What is this router’s role?

“Collapsed Backbone”

Science Dept

EngineeringDept

BusinessDept

Administration Dept

RemoteOffice

What is this router’s role?

Network segmentation device

192.168.4.0net

192.168.5.0net

What is this router’s role?

Network segmentation device(linking VLANs)

VLAN1

VLAN2

VLAN1

VLAN2

What is this router’s role?

Network segmentation device(linking VLANs)

VLAN1

VLAN2

ISL TrunkISL, Cisco’s Inter Switch Link, manages traffic from multiple VLANs over a single Ethernet pipe. ISL is covered in Semester 3.

What is this router’s role?

Security device (firewall)

Access control rules:1. Outbound traffic to Internet: YES2. Inbound traffic from Internet: NO

Fundamental router design

Routing protocols

Packet forwarding

Control plane

Forwarding plane(aka data plane)

Router

FIB

RIB

Software router

User-leveldaemons

routed, OSPFd,GNU Zebra, Quagga,XORP

OS kernel &Network devices

Linux, BSD,Click,NetFPGA, IXP

Commercial hardware router:Juniper

Routing Engine (RE)

Packet ForwardingEngine (PFE)

Control plane

Forwarding plane

Switch Control Board (SCB)

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ti-Se

rvic

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Mul

ti-Se

rvic

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• RE– x86 PC running JUNOS

• PFE– ASIC hardware and microcode

• MS-PIC– MIPS64-based XLR network processor– Each runs separate JUNOS

• JUNOS– FreeBSD-based OS for all Juniper routers

Routers

Modular FixedModular Routers

These type of routers have up gradable slots, and the number of ports can be increased just by adding cards in the slots.

Fixed Routers

These types of routers have fixed number of ports.

Why Use a Hierarchical Model?

• Reduces workload on network devices– Avoids devices having to communicate with too

many other devices (reduces “CPU adjacencies”)

• Constrains broadcast domains• Enhances simplicity and understanding• Facilitates changes• Facilitates scaling to a larger size

Hierarchical Network Design

Enterprise WANBackbone

Campus A Campus B

Campus C

Building C-1 Building C-2

Campus C Backbone

Core Layer

Distribution Layer

Access Layer

Cisco’s Hierarchical Design Model

• A core layer of high-end routers and switches that are optimized for availability and speed

• A distribution layer of routers and switches that implement policies and segment traffic

• An access layer that connects users via hubs, switches, and other devices

Router Interfaces

The console port is a management port used to provide out-of-band access to the router. It is used for the initial configuration of the router, monitoring, and disaster recovery procedures. To connect to the console port, a rollover cable and a RJ-45 to DB-9 adapter are used to connect a PC. Cisco supplies the necessary adapter to connect to the console port.