© 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 Router Source A Destination B

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 Gateway/Router Source A Destination B AA CC DDBB

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 AddressNetmaskGateway AddressInterfaceMetricPurpose Default Route Loopback Network Directly Attached Network Local Host Network Broadcast Multicast Address Limited Broadcast Routing Table of a Host IP Address Gateway 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