Lec1 lan switching


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Lec1 lan switching

  1. 1. Session 1 COMP 1161: Adv. Network and Security
  2. 2. Switching Technologies Overview Address learning Forwarding or filtering Looping avoidance – Spanning Tree Protocol LAN switch types
  3. 3. Switching Technologies Overview – layer 2 switch Advantages Hardware based (ASIC) Wire speed Low latency Low cost Disadvantages Can not break up broadcast domain Performance issue Network size limitation
  4. 4. Switching Technologies Comparison between switches & bridges Bridge – software based, one STP per bridge, up to 16 ports Switch – hardware based, many STP, hundreds of ports
  5. 5. Switching Technologies Switching functions Address learning Forward/filter decisions Loop avoidance
  6. 6. Switching Technologies Address learning - Layer-2 switches and bridges remember the source hardware address of each frame received on an interface and enter this information into a MAC database. Forward/filter decisions - When a frame is received on an interface, the switch looks at the destination hardware address and finds the exit inter-face in the MAC database.
  7. 7. Switching Technologies
  8. 8. Switching Technologies Loop avoidance - If multiple connections between switches are created for redundancy, network loops can occur. The Spanning-Tree Protocol (STP) is used to stop network loops and allow redundancy  Broadcast storm  Multiple frame copies  Thrashing(constantly updating the MAC filter table with same SA)  Multiple loops(generating throughout an internetwork)
  9. 9. Switching Technologies
  10. 10. Switching Technologies
  11. 11. Switching Technologies STP (Spanning Tree Protocol) Root bridge – reference point, the lowest bridge ID Root port – the port with the lowest cost to the root bridge Designated port – root bridge ports and non root bridge forwarding ports Non root bridge
  12. 12. Switching Technologies STP rule One root bridge per network subnet/VLAN One root port per non-root bridge One designated port per segment All ports of root bridges are designated ports
  13. 13. Switching Technologies Election rule – through BPDU Root bridge – highest priority (lowest priority value), lowest MAC address Root port – lowest cost to the root bridge Designated port – all root bridge ports, lowest cost to the root bridge, bridge ID
  14. 14. Switching Technologies
  15. 15. Switching Technologies
  16. 16. Switching Technologies STP port states Blocking – not forward frames but listen to BPDU (stable state) Listening - only receive BPDU Learning – learning MAC addresses, build MAC table Forwarding – send and receive data (stable state)
  17. 17. Switching Technologies
  18. 18. Switching Technologies  LAN switch types  Store and forward - the complete data frame is received on the switch’s buffer, a CRC is run, and then the destination address is looked up in the MAC filter table.  Cut through - the switch only waits for the destination hardware address to be received and then looks up the destination address in the MAC filter table.  Fragment free - the default for the Catalyst 1900 switch, it is sometimes referred to as modified cut-through. Checks the first 64 bytes of a frame for fragmentation (because of possible collisions) before forwarding the frame.
  19. 19. Switching Technologies
  20. 20. Switching Technologies