© N. Ganesan, All rights reserved. Chapter IP Routing

© N. Ganesan, All rights reserved.

Chapter

IP Routing

© N. Ganesan, All rights reserved.

Module 1

Address Resolution in IP Routing

IP Routing Defined

• The routing of data packets from one network segment to another– For example from from one subnet to

another subnet

• A router (gateway) is often involved in the routing process

A Routing Example

190.175.25.20Router

190.175.26.20

190.175.25.0

190.175.26.0

190.175.25.10

190.175.26.40

Source A

Destination B

190.175.26.40

Step 1: The Routing

• Computer A will analyze (AND)the data packet against its subnet masks– The data is to be sent to another subnet

• Broadcast for the hardware address (eg: CC) of the gateway (IP address is already known)– Using ARP

• On receiving the hardware address, send the data packet to the gateway (router) to be forwarded to its destination subnet

Step 2: The Delivery

• The router will now be able to deliver the data packet to its destination in the other subnet

• An analysis of the data packet (ANDing) will determine the destination subnet

• The gateway will broadcast for the hardware address of the receiving host (IP already known)

• On receiving a response, the packet will be forwarded to the destination host

IP and Hardware Addresses

190.175.25.20Gateway/Router190.175.26.20

190.175.25.10

190.175.26.40

Source A

Destination B

AA CC

DD BB

Major Routing Methods

• Static routing– Routing tables are hand maintained at the

router

• Dynamic routing– Routing tables are dynamically maintained by

the routing protocol– RIP (Routing Information Protocol)– Open Shortest Path First (OSPF) protocol

• Static and dynamic routings may be integrated

Entries in a Routing Table

• Network ID (Address)• Network (subnet) mask• Next hop (Gateway address) • Interface

– Network interface for forwarding the data packet

• Metric– Cost of each route for the selection of the

best hop

Network Address Netmask Gateway Address Interface Metric Purpose

0.0.0.0 0.0.0.0 157.55.16.1 157.55.27.90 1 Default Route

127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1 Loopback Network

157.55.16.0 255.255.240.0 157.55.27.90 157.55.27.90 1 Directly Attached Network

157.55.27.90 255.255.255.255 127.0.0.1 127.0.0.1 1 Local Host

157.55.255.255 255.255.255.255 157.55.27.90 157.55.27.90 1 Network Broadcast

224.0.0.0 224.0.0.0 157.55.27.90 157.55.27.90 1 Multicast Address

255.255.255.255 255.255.255.255 157.55.27.90 157.55.27.90 1 Limited Broadcast

Routing Table of a HostIP AddressGateway

Subnet Mask

Source: Micrsoft white paper on TCP/IP

Obtaining the Routing Table

• A routing table at a host or a server can be printed by issuing the following command– route print– The above command operates with

both Windows 9x and Windows NT

End of Module

© N. Ganesan, All rights reserved.

Module 2

Configuring a Router

Configuration of a Router with Windows NT

• Microsoft NT Server OS can be used to configure a server to act as a router as well

• Microsoft's MultiProtocol Router (MPR) service must be installed for this purpose

• Both TCP/IP and IPX routing along with DHCP relaying are supported

• Also, static and dynamic routing configurations are supported

Components of MPR

• Routing Information Protocol (RIP) for TCP/IP

• DHCP Relay Agent• RIP for IPX• Note: NetBEUI is not a routable

protocol

DHCP Relaying

• Designed to allow a DHCP server to exist on any subnet

• Each subnet need not have its own DHCP server

• A relay agent can relay the request for IP from one subnet to another subnet that contains the DHCP server

Router Hardware

• A router can be a standalone unit– CISCO routers

• A computer can be configured to function as a router– Such computers often have multiple

NICs to connect the different subnets together

– Such computers with multiple NICs are often called a multi-homed computer

An Example of Router Hardware Configuration

NIC 1

NIC 2

Subnet 1

Subnet 2

Computer configured as a router with Windows NT.

Enabling Static Routing on Windows NT

• Ensure that RIP service is installed and started– Use the Network Services in the

Service tab under Network properties to install RIP if necessary

• On the TCP/IP properties, select IP Forwarding to enable routing

Adding RIP from

Network Services

Selecting IP Forwarding

© N. Ganesan, All rights reserved.

End of Module

END OF CHAPTER