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9.1 | |
Trunking | |
| 9.1.2 | |
Trunking concepts |
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As mentioned before, a trunk is a physical
and logical connection between two switches across which network
traffic travels. It is a single transmission channel between two
points. Those points are usually switching centers.
In the context of a VLAN switching environment, a trunk is a
point-to-point link that supports several VLANs. The purpose of a trunk
is to conserve ports when creating a link between two devices
implementing VLANs. Figure
Adding a third VLAN would require using two
additional ports, one on each connected switch. This design is also
inefficient in terms of load sharing. In addition, the traffic on some
VLANs may not justify a dedicated link. Trunking will bundle multiple
virtual links over one physical link by allowing the traffic for several
VLANs to travel over a single cable between the switches.
A comparison for trunking is like a
Highway Distributor.
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illustrates
two VLANs shared across two switches, (Sa and Sb). Each switch is
using two physical links so that each port carries traffic for a
single VLAN. This is the simplest way of implementing inter-switch
VLAN communication, but it does not scale well.
The roads
with different starting and ending points share a main national highway
for a few kilometers then will divide again to reach their particular
destinations. This method is more cost effective than building an entire
road from start to end for every existing or new destination.
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