CS 350
Chapter-11
Switching
Switching Service
Hardware-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 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
Forward/Filter Decision
Switch#sh mac address-table
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
Source MAC: 0005.dccb.d74b
Destination MAC: 000a.f467.9e8c
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