CCNA 2 Capitulo 2

CCNA 2 Capitulo 2

1. SWITCHING CONCEPTS

   • FRAME FORWARDING
     • AN ETHERNET FRAME WILL NEVER BE FORWARDED OUT THE SAME PORT IT WAS ON WHICH IT WAS RECEIVED.
     • IS UNIVERSAL IN NETWORKING AND TELECOMMUNICATIONS
     • SWITCHES
       • ARE USED IN LAN , WANs & PSTN
       • INTEGRATED CIRCUITS AND ACCOMPANYING SOFTWARE
     • TWO TERMS FRAMES ENTERING AND LEAVING AN INTERFACE
       • INGRESS
         • PORT WHERE A FRAME ENTERS THE DEVICE
       • EGRESS
         • PORT HAT FRAME WILL USE WHEN LEAVING THE DEVICE
     • SWITCH LAN MAINTAINS A TABLE WHEN FORWARDING TRAFFIC THROUGH THE SWITCH
       • SWITCH MAC ADDRESS TABLE
         • STEP 1 - FORWARD - EXAMINING THE DESTINATION MAC ADDRESS
           • FORWARDING METHODS
             • TWO METHODS
               • STORE AND FORWARD
                 • TWO PRIMARY CHARACTERISTICS
                   • AUTOMATIC BUFFERING
                     • MISMATCH IN SPEED BETWEEN THE INGRESS AND EGRESS PORTS ?
                       • SWITCH STORES THE ENTIRE FRAME IN A BUFFER
                   • ERROR CHECKING
                     • 2) THE SWITCH COMPARES THE FRAME CHECK SEQUENCE (FCS)
                       • DROP
                         • FCS CHECK
                       • PASS
                         • FCS CHECK
                     • 1 - AFTER RECEIVING THE ENTIRE FRAME ON THE INGRESS PORT
                 • 1 - RECEIVED THE ENTIRE FRAME
                 • CISCOs PRIMARY LAN
                 • 2 - CHECKED THE FRAME FOR ERRORS
                   • USING A MATHETICAL ERROR-CHECKING MECHANISM CRC
               • CUR THROUGH
                 • TYPE
                   • 1) FRAGMENT FREE
                     • PROVIDES BETTER ERROR CHECKING THAN CUT-THROUGH WITH LATENCY
                     • STARTS FORWARDING THE FRAME AFTER IT HAS READ THE TYPE FIELD
                     • ANALYZES THE FIRST 64 BYTES OF THE PACKET.
                   • 2) FAST FORWARD
                     • VIEW ONLY DESTINATION AND FORWARD
                 • WITHOUT ANY ERROR CHECKING
                   • MAY FORWARD INVALID FRAMES BECAUSE NO FCS CHECK IS PERFORMED
                 • 1 - VIEW DESTINATION MAC OF INCOMING FRAME
                 • 2 - EGRESS PORT HAVE BEEN DETERMINED
                 • MORE APPROPRIATE HIGH PERFORMANCE COMPUTING (HPC)
                   • PROCESS-TO-PROCESS LATENCIES OF 10 MICROSECONDS OR LESS.
                 • NEGATIVE IMPACT
                   • HIGH ERROR RATE (INVALID FRAMES ) ?
                     • CAN HAVE A NEGATIVE IMPACT ON BANDWIDTH
                   • CAN FORWARD FRAMES WITH ERRORS
             • SOFTWARE ON APPLICATION-SPECIFIC INTEGRATED CIRCUITS (ASICS)
               • REDUCE THE FRAME-HANDLING TIME WITHIN THE DEVICE
               • ALLOW THE DEVICE TO MANAGE AN INCREASED NUMBER OF FRAMES , WITHOUT DEGRADING PERFORMANCE.
           • DESTINATION MAC IS IN THE TABLE
             • WHEN WILL IT BE UNICAST?
               • 1- SWITCH WILL LOOK FOR A MATCH DESTINATION MAC AND MAC TABLE
               • 2- FORWARD THE FRAME OUT OF THE SPECIFIED PORT
           • WHEN WILL IT BE UNKNOWN UNICAST
             • DESTINATION MAC IS NOT IN THE TABLE
               • THE SWITCH WILL FORWARD THE FRAME OUT ALL PORTS EXCEPT THE INCOMING PORT.
           • DESINATION MAC ADRESS IS BROADCAST / MULTICAST
             • FRAME IS FLOODED OUT ALL PORTS EXCEPT THE INCOMING PORT
         • STEP 1 - LEARN - EXAMING THE SOURCE MAC ADDRESS
           • MAC ADDRESS DOES EXIST IN THE TABLE BUT ON A DIFFERENT PORT
             • SWITCH THREATS THIS AS NEW ENTRY
           • SOURCE MAC DOES EXIST ?
             • SWITCH UPDATES THE
               • REFRESH TIMER FOT THAT ENTRY
           • SOURCE MAC DOES NOT EXIST IN THE MAC TABLE
             • MAC ADDRESS AND INCOMIMG PORT NUMBER ADDED TO THE TABLE MAC
           • EVERY FRAME ENTERS - BUILD MAC TABLE
             • INCOMING PORT NUMBER
             • MAC ADDRESS
         • FRAME ORDER
           • 1) MAC DESTINATION 2) MAC SOURCE
         • HOW SWITCH FORWARDING TRAFFIC ?
           • 1 - VIEW INGRESS PORT AND DESTINATIONS MAC ADDRESS
           • 2 - VIEW MAC ADDRESS TABLE
         • WHERE IS IT SAVED?
           • CAM TABLE (RAM)

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