CS 350Chapter-11Switching

Switching ServiceHardware-based bridging (ASIC: application-specific integrated circuits)

Wire speed

Low latency

Low cost

Bridging & Switching

Bridging Switching

Software-based Hardware-based (ASIC)

Multi-port bridge

Only one spanning-tree Many spanning-tree

Less ports More ports

Layer-2 broadcast Layer-2 broadcast

Exam MAC address Exam MAC address

Forwarding based on MAC address

Forwarding based on MAC address

Switch–Address LearningHost 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 tableForward to the destination

Destination is not in the tableForward 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

Forward/Filter DecisionSwitch#sh mac address-table

Source MAC: 0005.dccb.d74b Destination MAC: 000a.f467.9e8c

Vlan MAC Address Type Ports

------- ---------------------- -------- ---------

1 0005.dccb.d74b DYNAMIC Fa0/1

1 000a.f467.9e80 DYNAMIC Fa0/3

1 000a.f467.9e8b DYNAMIC Fa0/4

1 000a.f467.9e8c DYNAMIC Fa0/3

1 0010.7b7f.c2b0 DYNAMIC Fa0/3

1 0030.80dc.460b DYNAMIC Fa0/3

1 0030.9492.a5dd

DYNAMIC Fa0/1

1 00d0.58ad.05f4 DYNAMIC Fa0/1

Loop Avoidance

Spanning Tree Protocol -STP

Spanning-tree algorithm (STA)Bridge Protocol Data Units (BPDUs)

Spanning-tree port statesBlocking: 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

VLANStatic: Manually

DynamicManagement software

Management Database

VLAN Management Policy Server (VMPS) to set up database

Assignment based on hardware address, protocols, applications

Identifying VLANAccess Ports : one VLAN

Trunk Ports: multiple VLANsConnect varies VLANs without router (layer 3)

Inter-Switch Link (ISL)Tag VLAN information onto an Ethernet Frame

Proprietary to Cisco

IEEE 802.1QInsert a field into a frame to identify the VLAN

OthersPoE – power over Ethernet

Energy port

Port Mirroring/SpanningSniff traffic on a network using a switch

Place a port in spanning mode

Frame is caught by both the host and the sniffer