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© 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
