Syngress - Eleventh Hour Network+ Exam N10-004 Study Guide (11 ...

100 CHAPTER 6 TCP/IP and Routing
contain a number of elements in a specified order. Each of those elements is
required and each is described briefly here.
■ Network destination The network ID can be class-based, subnetted, or
supernetted.
■ Netmask The mask used to match the destination network with the IP
address in the data.
■ Next hop or gateway The IP address of the next router (a hop is one segment
between routers. If a packet has to go through two routers, that would be
two hops).
■ Interface Identifies which network interface is used to forward the packet.
Remember that every router has at least two interfaces.
■ Metric The metric is a number used to help determine the best route for the
packet. This typically is used to identify the route with the fewest hops. The
metric is often expressed as the cost of the route.
Routing tables can also store four specific types of routes:
■ Directly attached network IDs For packets destined for the local or attached
network. If the sending and receiving hosts are both on the same subnet,
for instance, the packet will be sent through this method.
■ Remote network IDs Any packets destined for networks reachable through
routers will be sent through this routing method.
■ Host routes A host route is a route to a specific IP address. This type of route
allows a packet to be sent to a specific IP address. The network ID is the IP
address of the destination host and the network mask is 255.255.255.255.
■ Default route The default route is used when a more specific network ID
or route cannot be found. When all else fails, the default route is used. This
is defined as a network ID of 0.0.0.0 and the network mask is 0.0.0.0.
Route Determination Process
Each IP packet has a destination IP address, which is used to determine how
the packet will be routed. Using the logical ANDing process, the destination
IP address and the subnet mask (or netmask) are compared. If they match, the
packet stays on the local network and is sent directly to the destination IP address.
If the destination IP address and the subnet mask do not match, the entries in the
routing table are compared with the destination IP address. If a match is found
(that is, if the destination IP address and the subnet mask AND to a value found
in the routing table), the packet is sent to the gateway listed in the routing table.
If no matching entries can be found, the packet is sent to the defined default
gateway. If more than one match is found in the routing table entries, the metric
is used and the route with the fewest hops is typically selected. To view the route
table on a Windows Server 2003 computer, access the command prompt, and
type route print.
If there is no matching entry in the routing table, the packet will be sent to the
default gateway for forwarding. When this process is complete, the resulting IP