CCNA 3 - Capitulo 6

CCNA 3 - Capitulo 6

1. NAT (NETWORK ADDRESS TRANSLATION )

   • ADVANTAGE OF NAT
     • USING RFC 1918 IPV4 , NAT HIDES INTERNAL IPV4 OF USERS AND DEVICES
       • PURPOSE OF NAT DOES NOT PROVIDE SECURITY
     • CONSERVES LEGALLY REGISTERED ADDRESSING SCHEME
       • BY ALLOWING THE PRIVATIZATION OF INTRANETS
     • INCREASE FLEXIBILITY WITH
       • MULTIPLE POOLS
       • POOLS BACKUP
       • LOAD BALANCING POOLS
     • CONSERVES ADDRESS THROUGH
       • APPLICATION PORT LEVEL MULTIPLEXING
   • DISAVANTAGES OF NAT
     • ONE DISADVANTAGE OF USING NAT IS ITS IMPACT ON NETWORK PERFORMANCE, ESPECIALLY FOR REAL-TIME APPLICATIONS LIKE VOIP.
       • INCREASES FORWARDING DELAY , BECAUSE TRANSLATIONS OF EACH IPV4 TAKES TIME
     • END TO END ADDRESSING IS LOST
       • THIS IS PROBLEM BECAUSE MANY APPLICATIONS DEPEND END TO END ADDRESSING
         • SECURITY APPLICATIONS
         • DIGITAL SIGNARURES
         • IPSEC
           • NAT MODIFIES VALUE IN THE HEADER , CAUSING INTEGRITY CHECKS TO FAIL
     • NAT SOLVES PROBLEM OF NOT HAVING ENOUGH IPV4
       • BUT IT CAN CREATE OTHER PROBLEMS
     • WHY DOES NAT CAUSE DELAY? WHEN A PACKET PASSES THROUGH A NAT DEVICE, THE ROUTER MUST:
       • INSPECT THE ENTIRE PACKET
       • DETERMINE WHETHER TRANSLATION IS REQUIRED
       • MODIFY THE IP ADDRESS IN THE HEADER ;
       • RECALCULATE THE IP CHECKSUM ; RECALCULATE THE TCP OR UDP CHECKSUM
     • NAT DELAYS AND CARRIER GRADE NAT (CGN)
       • BECAUSE THERE ARE NOT ENOUGH PUBLIC IPV4 ADDRESSES AVAILABLE
         • MANY ISPS NOW ASSIGN CUSTOMERS A PRIVATE IPV4 ADDRESS INSTEAD OF A PUBLIC ONE.
       • HOW DOES IT WORK?
         • 1. CUSTOMER'S ROUTER TRANSLATES THE PACKET FROM
           • PRIVATE IPV4 (RFC 1918) → TO THE PRIVATE IPV4 ADDRESS OF THE ISP (RFC 6598)
         • 2. BEFORE THE PACKET REACHES THE INTERNET, THE ISP PERFORMS NAT AGAIN:
           • PRIVATE ISP IP (RFC 6598) → PUBLIC ISP IP