CCNA 2 - Capitulo 14.2

CCNA 2 - Capitulo 14.2

1. ROUTING CONCEPTS

   • PACKET FORWARDING
     • END TO END PACKET FORWARDING
       • WHATS IS PRIMARY RESPONSABILITY OS THE PACKET FORWARDING ?
         • ENCAPSULATE PACKET APPROPRIATE DATA FRAME THE OUTGOING INTERFACWE
       • CAUTION : WHEN THE INTERFACE IS A POINT TO POINT (PS2) SERIAL CONNECTION
         • ROUTER ENCAPSULATES THE IPV4 INTO THE PACKET FRAME FORMAT USED BY EXIST INTERFACE HDLC ,PPP
         • SERIAL CONNECTION ALWAYS IS POINT TO POINT
     • PACKET FORWARDING MECHANISMS
       • 1.PROCESS OF SWITCHING
         • OLDER ; OBSOLET ; SLOW
         • RARELY IMPLEMENTED IN MODERN NETWORKS
         • HOW IT WORKS ?
           • 3. DESTINATION ADDRESS ENTRY ROUTING TABLE
             • AND DETERMINES EXIT INTERFACE
           • 1. FIRST PACKET ARRIVES ON THE INTERFACE
             • PACKET IS FORWARDED TO THE CPU (CONTROL PLANE)
           • 2.CPU PERFORMS ROUTING TABLE LOOKUP AND DETERMINE EXIT INTERFACE AND FORWARDS THE PACKET
         • MATH LONG HAND
       • 2.FAST SWITCHING CACHE
         • OLDER ; SUCCESSOR TO PROCESS SWITCHING
         • STORE NEXT HOP INFORMATION.
           • REMEMBERING FOR ANSWER SUBSEQUENT IDENTICAL PROBLEM
         • HOW IT WORKS ?
           • 1. FIRST PACKET ARRIVES ON AN INTERFACE
             • IT IS FORWARDED TO THE CONTROL PLANE (CPU)
           • 2. CONTROL PLANE ( CPU ) CHECKS THE FAST-SWITCHING CACHE
             • 3. IF CACHE ENTRY EXISTS → PACKET IS FORWARDED USING CACHED NEXT-HOP INFORMATION
             • 4. IF CACHE ENTRY DOES NOT EXIST → PACKET IS PROCESS-SWITCHED
           • 5. FLOW / NEXT-HOP INFORMATION IS ADDED TO THE FAST-SWITCHING CACHE
           • 6. SUBSEQUENT PACKETS ARE FORWARDED USING THE CACHE (NO CPU LOOKUP)
       • 3.CISCO EXPRESS FORWARDING (CEF)
         • MOST RECENT AND DEFAULT CISCO MECHANISM FOR ROUTERS AND MULTILAYER SWITCHES
         • HOW ITS WORK ?
           • 1. NETWORK CONVERGES (ROUTING TABLE BECOMES STABLE)
           • 2. CEF BUILDS THE FIB AND ADJACENCY TABLES
           • 3. PACKET ARRIVES ON AN INTERFACE
           • 4. PACKET IS FORWARDED USING THE FIB AND ADJACENCY TABLES
           • 5. ALL PACKETS ARE PROCESSED IN THE DATA PLANE AT HIGH SPEED
         • TABLES ENTRIES ARE NOT PACKET-TRIGGED LIKE FAST SWITCHING
           • BUT CHANGE TRIGGED , SUCH AS WHEN CHANGES IN THE NETWORK TOPOLOGY
         • "SPREADSHEET"
       • ROUTERS SUPPORT THE FOLLOWING THREE PACKETS FORWARDING MECHANISMS
     • DECISION PROCCESS - FORWARDING
       • AFTER DETERMINED BEST PATCH , IT MUSTH DETERMINE AND FORWARD
         • HOW TO ENCAPSULATE THE PACKET
         • CORRET EGRESS INTERFACE
       • 1.THE DATA LINK FRAME WITH AN ENCAPSULATED IP PACKET
         • ARRIVES ON THE INGRESS INTERFACE.
       • 4. THE ROUTER ENCAPSULATES THE PACKET IN A DATA LINK FRAME . AND FORWARDS IT OUT THE EGRESS INTERFACE
         • THE DESTINATION COULD BE A
           • 1.DEVICE CONNECTED TO THE NETWORK
             • FORWARDED DIRECTLY TO THE DESTINATION DEVICE
             • EXPANDED DETAILS FORWARDING
               • HOW WILL THE ROUTER ENCAPSULATE THE PACKET IF IT DOESN'T KNOW THE DESTINATION MAC ADDRESS?
                 • IPV4 ADDRESS
                   • 1.AFTER CHECKING THE ARP TABLE AND VERIFYING THAT THERE IS NO IP AND MAC ADDRESS MATCH, AN ARP REQUEST IS MADE
                   • 2.ROUTER DESTINATION WILL RETURN AN ARP REPLY
                 • IPV6 ADDRESS
                   • 1. THE ROUTER SENDS AN ICMPV6 NEIGHBOR SOLICITATION (NS) MESSAGE
                   • 2. THE DESTINATION DEVICE WILL RETURN AN ICMPV6 NEIGHBOR ADVERTISEMENT (NA) MESSAGE WITH ITS MAC ADDRESS.
               • THE ROUTER ONLY ENCAPSULE AND FORWARDS THE DATA BECAUSE IT ALREADY KNOWS THE DESTINATION MAC ADDRESS.
           • 2.A NEXT-HOP ROUTER.
             • EXPANDED DETAILS FORWARDING THE DIFFERENCE DEVICE CONNECTED IS THAT ROUTER WILL SEARCH FOR
               • IP OF THE NEXT HOP ROUTER IN ITS ARP TABLE OR NEIGHBOR CACHE
       • 2.THE ROUTER EXAMINES THE DESTINATION IP ADDRESS IN THE PACKET HEADER
         • AND CONSULTS ITS IP ROUTING TABLE.
       • 3. THE ROUTER FINDS THE LONGEST MATCHING PREFIX IN THE ROUTING TABLE.
       • 5. HOWEVER, IF THERE IS NO MATCHING ROUTE ENTRY
         • THE PACKET IS DROPPED.