Switches and Bridges at the Data Link Layer
Written on 09:29 by Ahmet Emir
Layer 2 switching is advised hardware-based bridging because it uses specialized hardware
called an application-specific chip ambit (ASIC). ASICs can run up to gigabit speeds
with actual low cessation rates.
Latency is the time abstinent from back a anatomy enters a anchorage to the time it
exits a port.
Bridges and switches apprehend anniversary anatomy as it passes through the network. The band 2 device
then puts the antecedent accouterments abode in a clarify table and keeps clue of which anchorage the frame
was accustomed on. This advice (logged in the bridge’s or switch’s clarify table) is what helps
the apparatus actuate the area of the specific sending device. Figure 1.16 shows a switch
in an internetwork.
The absolute acreage business is all about location, location, location, and it’s the aforementioned way for both
layer 2 and band 3 devices. Though both charge to be able to accommodate the network, it’s acute to
remember that they’re anxious with actual altered genitalia of it. Primarily, band 3 machines (such
as routers) charge to locate specific networks, admitting band 2 machines (switches and bridges)
need to eventually locate specific devices. So, networks are to routers as alone accessories are
to switches and bridges. And acquisition tables that “map” the internetwork are for routers as filter
tables that “map” alone accessories are for switches and bridges.
After a clarify table is congenital on the band 2 device, it will advanced frames alone to the segment
where the destination accouterments abode is located. If the destination accessory is on the aforementioned segment
as the frame, the band 2 accessory will block the anatomy from activity to any added segments. If
the destination is on a altered segment, the anatomy can be transmitted alone to that segment. This
is alleged cellophane bridging.
26 Chapter 1 Internetworking
When a about-face interface receives a anatomy with a destination accouterments abode that isn’t found
in the device’s clarify table, it will advanced the anatomy to all affiliated segments. If the unknown
device that was beatific the “mystery frame” replies to this forwarding action, the about-face updates
its clarify table apropos that device’s location. But in the accident the destination abode of the
transmitting anatomy is a advertisement address, the about-face will advanced all broadcasts to every connected
segment by default.
FIGURE 1 . 1 6 A about-face in an internetwork
All accessories that the advertisement is forwarded to are advised to be in the aforementioned broadcast
domain. This can be a problem; band 2 accessories bear band 2 advertisement storms that choke
performance, and the alone way to stop a advertisement storm from breeding through an internetwork
is with a band 3 device—a router.
The better account of application switches instead of hubs in your internetwork is that each
switch anchorage is absolutely its own blow domain. (Conversely, a hub creates one ample collision
domain.) But alike armed with a switch, you still can’t breach up advertisement domains. Neither
switches nor bridges will do that. They’ll about artlessly advanced all broadcasts instead.
Another account of LAN switching over hub-centered implementations is that anniversary device
on every articulation acquainted into a about-face can address simultaneously—at least, they can as long
as there is alone one host on anniversary anchorage and a hub isn’t acquainted into a about-face port. As you might
have guessed, hubs acquiesce alone one accessory per arrangement articulation to acquaint at a time.
If you enjoyed this post Subscribe to our feed