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Learn about the advantages and limitations of layer-2 switching in computer networks. Hardware-based with MAC address efficiency, it offers increased bandwidth but has broadcast domain limitations. Understand how Address Resolution Protocol (ARP) works and master the Spanning Tree Protocol (STP) to prevent network loops and ensure optimal data transmission. Explore root bridge selection, port states, and bridge operation for a robust network design.
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Layer-2 Switching • Advantages: • Hardware based (Uses the MAC address from the host’s NIC card) • Not software devices • Fast and efficiency • Increases the bandwidth for each user • Limitations: • Does not break up broadcast domains • Make sure users spend 80% of time on the local segment
ARP (DNS) 0200.2222.2222 E01 1 DMAC:FFFF.FFFF.FFF SMAC: 0200.222.2222 ARP 0200.2222.2222 E01 0200.1111.1111 E03 2 DMAC:0200.2222.2222 SMAC: 0200.1111.1111 ARP Request 3 DMAC: 0200.1111.1111 SMAC: 0200.2222.2222 ARP 4 DMAC: 0200.2222.2222 SMAC: 0200.1111.1111 ARP (web) 5 DMAC: FFFF.FFFF.FFFF SMAC: 0200.1111.1111 0200.2222.2222 E01 0200.1111.1111 E03 0200.3333.3333 E02 6 DMAC: 0200.1111.1111 SMAC: 0200.3333.3333 Address Learning WWW:0200.3333.3333 PC:0200.2222.2222 DNS:0200.1111.1111 E01 E02 E03
Forward/Filter Decisions • When a frame arrives: • Case 1: DMAC is known and in the database • Case 2: DMAC is not listed • Case 3: It is a broadcast
Loop Avoidance • Redundant links are use between switches/bridges to increase survivability • Disadvantages: • Broadcast storms • Trashing the MAC table
Spanning Tree Protocol (STP) • STP is used to avoid networks loops on layer-2 networks (bridges and switches) • STP is a bridge protocol that make sure that transmission takes place over a spanning tree topology • Spanning tree terms: • Root Bridge: • the bridge with the best bridge ID • all decision in the network are made on this bridge • Bridge ID: • lowest bridge ID becomes the root bridge
Nonroot Bridge • Bridge Protocol Data Unit (BPDU) • Root Port • The link directly connected to the root bridge, or the shortest path to the root bridge • Designated/Nondesignated port • Port cost • Forwarding port • send and receives all data • Blocked port • does not participate in frame forwarding
Spanning-Tree Operations • Selecting the root bridge • Selecting the designated port • Port States • Blocking • Listening • Learning • Forwarding • Disabled