What is
IP forwarding?
An Internet environment results from the
interconnection of physical networks by routers. Each router is connected
directly to two or more networks, hosts are generally connected to a single
network, but this is not mandatory.
There are several types of routes:
• Direct routing. This is the case if
the two machines who want to communicate are attached to the same network and
therefore have the same IP network number. It may be two hosts or a router and
a host. It is sufficient to perform the transport of the IP packet to determine
the recipient’s physical address and encapsulate the datagram in a frame before
sending it over the network.
• Indirect Routing. In this case,
routing is more complex because it must determine the router to which
datagram’s are sent. The latter can thus be forwarded from router to router
until they reach the destination host. The routing function is mainly based on
the routing tables. Routing is done from the network number of the IP address
of the destination host. The table contains for each network number to reach
the IP address of the router to send the datagram. It may also include a
default router address and direct routing indication. The difficulty comes from
the routing initialization and updating of routing tables.
• The subnetting. This addressing
technical and standardized routing to manage multiple physical networks from a
single Internet IP address. The principle of subnetting is to
divide the host number portion of an IP address subnet number and host number.
Outside the site, the addresses are interpreted without taking account of
subnetting, cutting being seen and treated from the inside. Redistribution
number allows the host to choose freely the number of machines based on the
number of networks on the site. Conceptually, the addressing techniques and
routing are the same. At the physical level, we use an address mask.
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