Page 19 / 141
DTUS065 rev A.7 – June 27, 2014
V
TECHNICAL REFERENCE
V.1
Addressing in network protocols
In a device bearing multiple LAN interfaces the IP protocol can route data
packets from LAN to LAN considering its final target that may be several
“hops” farther.
If the LANs are compatible from the viewpoint of addresses and data frames
structure, the device can also implement a bridge, moving blindly data
frames without considering the final target.
Each of these levels of data transfer uses its own addressing scheme.
IP networks can be conceptually grouped into “zones” in order to assign
common administrative policies to them.
V.1.1
TCP/IP network layers
V.1.1.1
TCP/IP protocols stack
TCP/IP is the name of the protocols used by Internet and most Intranets.
In a device participating in a TCP/IP network, there are four software layers:
the
application layer
, the
transport layer
(TCP or UDP), the
network
layer
(IP), the
LAN layer
(Ethernet, Wi-Fi, point-to-point modems, etc.)
Each layer has its own purpose and addressing scheme.
The
LAN layer address
allows a device to send data to another device
connected to the same LAN. But there is not enough information in a LAN
address to send to a device connected on another LAN through a router.
The
Network (IP) address
solves this problem by defining addresses which
can be subject to routing. When the source and destination devices are not
on the same LAN, the source device can send data to an intermediate router
(also called gateway). The router has routing tables which allows it to
forward data to the destination device, maybe through other gateways.
The
transport layer address,
called a “port”, is used inside a destination
device to deliver data to the correct application process.
You can move packets between two physical links depending on their MAC
addresses, without changing the packets: this is called bridging or switching.
You can move packets between LANs by selecting their destination
depending on the IP addresses: this is called routing. Routing offers
additional features, like the possibility to masquerade IP addresses, or to
selectively disable routing: this is firewalling.
