Cisco WS-C2950-24 - How VLAN Trunks Work

Chapter 8 Configuring VLANs
How VLAN Trunks Work
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Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
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How VLAN Trunks Work
A trunk is a point-to-point link that transmits and receives traffic between
switches or between switches and routers. Trunks carry the traffic of multiple
VLANs and can extend VLANs across an entire network. 100BASE-T and
Gigabit Ethernet trunks use Cisco Inter-Switch Link (ISL), the default protocol,
or industry-standard IEEE 802.1Q to carry traffic for multiple VLANs over a
single link.
Figure 8-4 shows a network of switches that are connected by ISL trunks.
Figure 8-4 Catalyst 2900 XL and Catalyst 3500 XL Switches in an ISL Trunking Environment
Catalyst 5000 series
switch
Catalyst
2900 XL
switch
Catalyst
3500 XL
switch
Catalyst
2900 XL
switch
Catalyst
3500 XL
switch
VLAN2
VLAN3VLAN1
VLAN1
VLAN2
VLAN3
ISL
trunk
ISL
trunk
ISL
trunk
ISL
trunk
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