{"id":55,"date":"2015-08-22T23:31:59","date_gmt":"2015-08-22T23:31:59","guid":{"rendered":"http:\/\/wiki.thomasandsofia.com\/?p=55"},"modified":"2015-09-06T20:19:01","modified_gmt":"2015-09-06T20:19:01","slug":"ccent-3-s01-e10-lans-understanding-lan-switches","status":"publish","type":"post","link":"https:\/\/wiki.thomasandsofia.com\/?p=55","title":{"rendered":"CCENT 3 S01 E10 \u2013 LANS: Understanding LAN Switches"},"content":{"rendered":"<h3>The Problem with Shared CSMA\/CD<\/h3>\n<p>Carrier Sense Multiple Access \/ Collision Detection<\/p>\n<p>Hubs and Switches perform the same function, but are significantly different.<\/p>\n<ul>\n<li>Hubs send all incoming signals to all connected PCs.<\/li>\n<li>Hubs work at the Physical Layer, sees the signal and sends it out.<\/li>\n<li>Hub Speeds are very fast &#8211; Wire Speed.<\/li>\n<li>No difference between Unicast, Broadcast or Multicast<\/li>\n<li>1 Collision Domain: Only one device can send at a single time<\/li>\n<li>1 Broadcast Domain: One broadcast will travel through every Hub connected to it.<\/li>\n<li>The more PCs you connect, the more collisions you&#8217;ll get and transmissions rates slow significantly.<\/li>\n<\/ul>\n<h4>Understanding Collisions<\/h4>\n<ul>\n<li>One of the colliding devices will send a &#8220;Jam Signal&#8221;<\/li>\n<li>It will halt all communication for a random amount of time (&lt;1 second) before attempting to resend.<\/li>\n<li>After both devices have sent their data, the Jam is released and traffic can resume as normal.<\/li>\n<\/ul>\n<h4>Understanding Bridges<\/h4>\n<p><a href=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/hub-bridge.png\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-61\" src=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/hub-bridge.png\" alt=\"hub-bridge\" width=\"640\" height=\"410\" srcset=\"https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/hub-bridge.png 640w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/hub-bridge-300x192.png 300w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/hub-bridge-150x96.png 150w\" sizes=\"auto, (max-width: 640px) 100vw, 640px\" \/><\/a><\/p>\n<p>&nbsp;<\/p>\n<ul>\n<li>Bridges connect between hubs and learn MAC addresses.<\/li>\n<li>By using a Bridge, you divide your network into 2 Collision Domains (or more, depending on # of ports on the bridge.)<\/li>\n<li>This allows both Collision Domains to sent amongst themselves without creating collisions.<\/li>\n<li>Bridges were popular between Mid &#8217;80s to early 90&#8217;s<\/li>\n<li>Bridges were slow.\u00a0 MAC address learning done via software.<\/li>\n<\/ul>\n<h4>Understanding Switches<\/h4>\n<ul>\n<li>Switches operate at the Data Link Layer because it &#8220;Sees&#8221; MAC addresses and can learn them.<\/li>\n<li>Each Switchport is a Collision Domain &#8211; All devices can Transmit at the same time!<\/li>\n<li>Allow Full Duplex Communications (Can Transmit and Receive Simultaneously.)<\/li>\n<li>MAC Learning done via ASIC chip (Application Specific Integrated Circuit) so very fast!<\/li>\n<li>Switches are as fast as Hubs &#8211; Wire Speed!<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<h3>Understanding Collision Domains and Broadcast Domains<\/h3>\n<p>Collision Domain: How many devices can send or receive at the same time.<\/p>\n<p>Broadcast Domain: How far a signal can travel before it stops.<\/p>\n<p>&nbsp;<\/p>\n<h3>How a Switch&#8230;Switches!<\/h3>\n<p><a href=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/switch-cam-table.png\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-65\" src=\"http:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/switch-cam-table.png\" alt=\"switch-cam-table\" width=\"1282\" height=\"654\" srcset=\"https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/switch-cam-table.png 1282w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/switch-cam-table-300x153.png 300w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/switch-cam-table-1024x522.png 1024w, https:\/\/wiki.thomasandsofia.com\/wp-content\/uploads\/2015\/08\/switch-cam-table-150x77.png 150w\" sizes=\"auto, (max-width: 1282px) 100vw, 1282px\" \/><\/a><\/p>\n<ul>\n<li>Switches ONLY Learn a MAC Address when that connection Transmits<\/li>\n<li>If PC-A sends an ARP, looking for PC-B:\n<ul>\n<li>It sends its MAC as the Source MAC<\/li>\n<li>It sends FFFF:FFFF:FFFF as the Destination MAC<\/li>\n<li>This designates that ALL recipents should LISTEN to the Packet!<\/li>\n<\/ul>\n<\/li>\n<li>The Switch receives the ARP and learns the location of PC-A<\/li>\n<li>The Switchport and MAC are then stored in the CAM Table (Content Addressable Memory)<\/li>\n<li>When PC-B receives the ARP, it replies with its MAC, which is then stored.<\/li>\n<li>It takes a Switch &lt;15 Seconds to learn all MAC addresses connected to it.<\/li>\n<\/ul>\n<h4>If a Switch DOES NOT KNOW a MAC Address:<\/h4>\n<ul>\n<li>Assume PC-A already knows the MAC address of PC-C, it will encode both the Source MAC and Destination MAC in the Packet.<\/li>\n<li>The Switch receives the Packet and not knowing which Switchport owns the Destination MAC, so it sends to ALL Switchports (Except the Sending) with FFFF:FFFF:FFFF (Broadcast)<\/li>\n<li>Only the correct owner of the IP address embedded as the Destination Address will respond and in doing so will send the correct MAC for the Switch to learn.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The Problem with Shared CSMA\/CD Carrier Sense Multiple Access \/ Collision Detection Hubs and Switches perform the same function, but are significantly different. Hubs send all incoming signals to all connected PCs. Hubs work at the Physical Layer, sees the signal and sends it out. Hub Speeds are very fast &#8211; Wire Speed. No difference ..<\/p>\n<div class=\"clear-fix\"><\/div>\n<p><a href=\"https:\/\/wiki.thomasandsofia.com\/?p=55\" title=\"read more...\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3,2,5],"tags":[],"class_list":["post-55","post","type-post","status-publish","format-standard","hentry","category-ccent","category-networking","category-switches"],"_links":{"self":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts\/55","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=55"}],"version-history":[{"count":9,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts\/55\/revisions"}],"predecessor-version":[{"id":67,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts\/55\/revisions\/67"}],"wp:attachment":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=55"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=55"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=55"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}