CS 350 Chapter-11Switching

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

Bridging & Switching BridgingSwitching Software-basedHardware-based (ASIC) Multi-port bridge Only one spanning-treeMany spanning-tree Less portsMore ports Layer-2 broadcast Exam MAC address Forwarding based on MAC address

Switch–Address Learning Switch–Address Learning Host A sends a frame to Host B A: C01.000A B: C01.000B 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

Forward/Filter Decision Forward/Filter Decision Switch#sh mac address-table Source MAC: 0005.dccb.d74b Destination MAC: 000a.f467.9e8c VlanMAC AddressTypePorts dccb.d74bDYNAMICFa0/1 1000a.f467.9e80DYNAMICFa0/3 1000a.f467.9e8bDYNAMICFa0/4 1000a.f467.9e8cDYNAMICFa0/ b7f.c2b0DYNAMICFa0/ dc.460bDYNAMICFa0/ a5ddDYNAMICFa0/1 100d0.58ad.05f4DYNAMICFa0/1

Loop Avoidance

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

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

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

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