1. Chapter 6 – Routing

2. What is IP Routing?
IP Routing is the process of sending data from a host on one network to a remote host on another network through a router, or routers
Routers are referred to as gateways
Gateways have two or more network connections

3. Routing Table Each router maintains a routing table
The routing table specifies the path that the router uses to deliver a packet to a specified remote host
Routing tables maintain entries of where networks are located, not hosts
ARP is used in determining routing table entries

4. Dynamic versus Static Routing
There are two types of routing tables: static tables and dynamic tables.
Static tables are maintained by network manager
Dynamic tables are maintained by a routing protocol

5. Windows NT Server 4.0 as a router
NT Server can perform as an IP router using either static or dynamic routing
NT server can be configured with multiple network adapters and can route between them
This arracngement is referred to as a multihoned computer
Supports dynamic routing through use of RIP (Routing Information Protocol)

6. Static Routing Routing tables are built and maintained manually
If a route changes, static routers do not share this information with each other
Static routing tables consist of five columns of data

7. Five Columns in Routing Table
Destination- Can be an IP network or host address
Network mask – Subnet mask associated with Destination IP address
Forwarding IP Address – IP address to which the datagram is to be forwarded
Interface – Logical or physical interface used when forwarding datagram. Windows 2000 uses uses the IP address of the interface
Metric – Estimate of the number of hops (the number of routers to the destination)

8. Route Determination Process
Determine which routes in the routing table match the destination IP address by performing logical AND operation on destination IP address and Network Mask (in 2nd column of table). Compare results with Destination filed
From those routes that match, select the route(s) having the most number of 1 bits in the Network Mask field
From the step above, select route with the lowest metric

9. Route Determination Process – Cont.
The above process results in a single route
The single route chosen yield the forwarding IP address and interface over which to forward the datagram
If no match is found, IP indicates a routing error
You can see the routing table using the command: route print

10. Some Specific Routes In Routing Table
Destination and Network mask of is the default when there are no other matches. The packet is in this case forwarded to the default gateway
Destination of and Network Mask of is the Loopback Network Route where all datagrams are forwarded to the reserved loopback address

11. Specific Routes – Cont.
Route to local subnet is indicated by Destination having local host IP address and local host subnet.
Local Host route has IP address of local host for Destination and for subnet mask

12. Windows 2000 IP Routing Process
Perform the route determination process described above to choose a single route
From the single route, examine the gateway and interface IP addresses
If these are the same, set the forwarding IP address to the original destination IP address
If they are different, set the forwarding IP address to the gateway IP address
The forwarding IP address is then sent to ARP to determine the MAC address associated with this IP address

13. Example of Routing Table
Use route print command to vies routing table of your machine

14. Examples of Windows 2000 Route Determination
See Page 150 of text for sample routing table
Example of Local traffic
Example of Remote traffic