CCNA 2 - Capitulo 5

CCNA 2 - Capitulo 5

1. STP - SPANNING TREE PROTOCOL ( 802.1D) CONCEPTS

   • PURPOSE OF STP
     • PREVETING DISRUPTION OF NETWORK BECAUSE OF LOOPS
     • ALLOWS REDUNDANCY CREATING A LOOP FREE LAYER 2
     • REDUNDANT NETWORKS ELIMINATING SINGLE POINTS OF FAILURE MUST BE
       • PHYSICAL REDUNDANCY
       • LOGICAL REDUNDANCY
     • WHAT IS A LOOP-FREE TOPOLOGY? ?
       • SINGLE PATH BETWEEN ANY TWO DEVICES
   • THE SPANNING TREE ALGORITHM - STA
     • SELECTING SINGLE ROOT BRIDGE
       • OTHER SWITCHS DETERMINE A SINGLE LEAST COST PATH
     • STP IS BASED ON AN ALGOTITHM INVENTED BY RADIA PERLMAN
       • HOW DOES IT WORK?
         • 1 - BY SELECTING A SINGLE ROOT BRIDGE
         • 2 - OTHER SWITCHES DETERMINE A SINGLE LEAST COST PATH
       • IS ALGORITHM CREATES A LOOP FREE TOPOLOGY
     • HOW DOES IT WORK?
       • 1 - SELECT THE ROOT BRIDGE
       • 2 - BLOCK REDUNDANT PATHS
         • STP ALGORITHM ENSURE ONE LOGICAL PATH
         • REDUNDAT PATHS THAT COULD CAUSES LOOP ?
           • BLOCKING STATE PORTS
       • 3 - LOOP FREE TOPOLOGY
         • ONLY PATH BEETWEN ALL DESTINATIONS
         • BLOCKED PORT = NON FORWARDING LINK
       • 4 - LINK FAILURE CAUSES RECALCULATION
         • LINK FAILURE ?
           • DYNAMICALLY UNBLOCKING PORTS AND PERMITTING TRAFFIC
         • CAUTION : CAN ALSO OCCUR ANY TIME A NEW SWITCH OR NEW INTER SWITCH IS ADDES TO THE NETWORK
   • BROADCAST STORM
     • UNKNOWN UNICAT ; BROADCAST E MULTICAST
     • NEW TRAFFIC IS DISCARDED
     • WHATS IS ?
       • ABNORMALLY HIGH NUMBER OF BROADCASTS OVERHELMIMG THE NETWORK SPECIFIC AMOUNT OF TIME
     • CAN BE CAUSED BY A
       • HARDWARE PROBLEM - FALTY NIC
       • LOOP IN THE NETWORK
   • DESIGN LAYER 2 NETWORKS MUST BE REDUNDANT HOWEVER, THIS CAUSES A PROBLEM.
     • LAYER 2 LOOPS
   • WHATS IS LOOP ?
     • "REDUNDANT PATHS EXIST AND TRAFFIC CIRCULATES INDEFINITELY, CAUSING NETWORK INSTABILITY"
     • "FRAME UNTIL A LINK IS DISRUPTED AND BREAKS THE LOOP"
   • HOW CAN WE SOLVE A LAYER 2 LOOP?
     • SPANNING TREE PROTOCOL
   • WHATS IS STP RECALCULATIONS ?
     • WHEN A FAILURE OCCURS, STP UNBLOCKS A PREVIOUSLY BLOCKED PORT
       • TO RESTORE CONNECTIVITY WHILE PREVENTING LOOPS.
   • ISSUES WITH REDUNDANT SWITCH LINKS
     • LAYER 2 LOOP RESULT
       • BROADCAST TRANSMITTED INDEFINITELY
       • MAC TABLE INSTABILITY
       • HIGH CPU UTILIZATION
       • LINK SATURATION
     • LAYER 3 DOES MECHANISM RECOGNIZE AND ELIMINATE LOOP WITH
       • TIME TO LIVE (TTL) - IPV4 AND HOP LIMIT - IPV6
   • LAYER 2 LOOPS WITHOUT STP ENABLE
     • THEY CAN BE ENHANCED WITH
       • BROADCAST AND MULTICAST , UNKNOWN FRAMES
   • CISCO SWITCHES STP IS ENABLED BY DEFAULT