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CS 350

CS 350. Chapter-11 Switching. Switching Service. Hardware-based bridging (ASIC: application-specific integrated circuits) Wire speed Low latency Low cost. Bridging & Switching. Switch–Address Learning. Host A sends a frame to Host B A: 0000.8C01.000A B : 0000.8C01.000B

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CS 350

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  1. CS 350 Chapter-11 Switching

  2. Switching Service • Hardware-based bridging (ASIC: application-specific integrated circuits) • Wire speed • Low latency • Low cost

  3. Bridging & Switching

  4. Switch–Address Learning • Host A sends a frame to Host B • A: 0000.8C01.000A • B: 0000.8C01.000B • The switch receives the frame on the E0/0 interface • Place the source into MAC address table • Destination is in the table • Forward to the destination • Destination is not in the table • Forward to all interfaces except the source • Host B receives the frame and responses • The switch adds destination to MAC address table • Point-to-point connection from host A to B

  5. Forward/Filter Decision • Switch#sh mac address-table • Source MAC: 0005.dccb.d74b Destination MAC: 000a.f467.9e8c

  6. Loop Avoidance

  7. Spanning Tree Protocol -STP • Spanning-tree algorithm (STA) • Bridge Protocol Data Units (BPDUs) • Spanning-tree port states • Blocking: don’t forward frames; listen to BPDUs. • All ports are in blocking state by default when powered up • Listening: Listen to BPDUs to make sure no loops; dont populate the MAC address table • Learning: Listen to BPDUs; learn all paths; populate MAC address table; don’t forward frames; 15s to transit from listening to learning • Forwarding: send and receive frames; designated or root port turn to forwarding state at the end of learning state • Disabled: block from forwarding or STP; receive BPDUs without response; can return to listening after turning into designated or root port • Convergence: either forwarding or blocking mode

  8. VLAN • Static: Manually • Dynamic • Management software • Management Database • VLAN Management Policy Server (VMPS) to set up database • Assignment based on hardware address, protocols, applications

  9. Identifying VLAN • Access Ports : one VLAN • Trunk Ports: multiple VLANs • Connect varies VLANs without router (layer 3) • Inter-Switch Link (ISL) • Tag VLAN information onto an Ethernet Frame • Proprietary to Cisco • IEEE 802.1Q • Insert a field into a frame to identify the VLAN

  10. Others • PoE – power over Ethernet • Energy port • Port Mirroring/Spanning • Sniff traffic on a network using a switch • Place a port in spanning mode • Frame is caught by both the host and the sniffer

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