Transcript IP Routing

Chapter
IP Routing
© N. Ganesan, All rights reserved.
Module 1
Address Resolution in IP Routing
© N. Ganesan, All rights reserved.
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
Source A
190.175.25.10
190.175.25.0
A Routing Example
190.175.26.40
190.175.25.20
Router
190.175.26.20
Destination B
190.175.26.0
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
Source A
190.175.25.10
AA
CC
190.175.25.20
Gateway/Router
190.175.26.20
DD
Destination B
BB
190.175.26.40
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
Source: Micrsoft
white paper on TCP/IP
Network Address
Routing Table of a Host
Netmask
Gateway Address
Gateway
Interface
Metric
Purpose
IP Address
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
Subnet Mask
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
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
Module 2
Configuring a Router
© N. Ganesan, All rights reserved.
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
Subnet 1
Computer configured as a router with
Windows NT.
NIC 1
NIC 2
Subnet 2
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
End of Module
END OF CHAPTER
© N. Ganesan, All rights reserved.