Cisco Ethernet switches to play broader roles (How do Ethernet Switches work anyway?)

“Cisco Ethernet switches to play broader roles” - says an article under Trend Analysis, on page 11 of March 22, 2010 issue of Network World…

* But did you know? That Ethernet Switches aren’t affected by a looming change of IP Standards (See my IPv6 article below)? Nope it will just hop across them the same as IPv4 does.

http://en.wikipedia.org/wiki/OSI_model

Ethernet switches operate at the Data Link Layer, the second rung up the ladder on the way to your software (Application) on your computer. There are 7 layers altogether in this model, which is used as a Reference Model, for how things actually work. Layer 1, the Physical Layer is where wires are connected together to Ethernet Switches and Computers. This is where “signaling” occurs and things are pretty much encoded and decoded in binary. That’s a pretty low level, eh?

Layer 2 deals with “Physical Addressing” but that doesn’t mean IP Addressing it means “MAC” addressing. Thats those long Hexadecimal Addresses that every network card from wired to wireless has. At this level the Ethernet Switch doesn’t know and doesn’t care about IP Addressing. You could be talking about frogs or military aircraft and Layer 2 wouldn’t be any wiser about it. In an Ethernet Switch, as opposed to an old-style Network Hub (which basically just blasted every message to ever computer wether they wanted it or not), *it* keeps track of which MAC addresses are present on each of its ports (those jacks that you plug CAT5 or CAT6 RJ45 connector-type cables into) and builds a table for “Fast Switching” of Ethernet Frames (ethernet smallest unit of messaging) to the correct port. That’s how traffic gets to a port on an Ethernet Switch.

So if an Ethernet Switch is dealing with Ethernet Frames and Mac Addresses - how in the heck do you get IP Traffic (Internet Traffic) to a computer?

Enter “Arp” - Address Resolution Protocol. All computers, in their TCP/IP implementation know how to use a broadcast protocol called ARP. Arp basically are messages sent out by your computer, by the TCP/IP Stack over your Ethernet Card, saying “Arp who has 192.168.1.1?”. The computer that actually has the IP Address 192.168.1.1 answers something like this: “Arp 192.168.1.1 is *me* at MAC address aa:bb.cc:dd:ee:ff:a1:b2″. And from then on, for a little while, all traffic for that IP Address is sent to that MAC address … which our friendly Ethernet Switch knows is on one particular port.

Wireless, forget about the 802.11a/b/g/n protocols, works pretty much the same way. A wireless access point acts as if it were a Port on an Ethernet Switch. Aside from any router functionality that might be in an Access/Router combo unit, it’s just a fancy “wireless Ethernet Switch”.

How about that????

—
Alan Spicer
 
DBA Alan Spicer Telcom / Alan Spicer Marine Telecom
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This entry was posted on 26. March 2010 at 22:58 and is filed under Computer Networking onboard Sail and Motor Yachts. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response or trackback from your own site.