Trunk Connections
Unlike access-link connections, trunk connections are capable of carrying traffic for
multiple VLANs. To support trunking, the original Ethernet frame must be modified
to carry VLAN information, commonly called a VLAN identifier or number. This
ensures that the broadcast integrity is maintained. For instance, if a device from
VLAN 1 has generated a broadcast and the connected switch has received it, when
this switch forwards it to other switches, these switches need to know the VLAN
origin so that they can forward this frame out only VLAN 1 ports and not other
chapter 13 page396
EtherChannels
It is common to need higher bandwidth speeds for certain kinds of connections in
your network, such as connections from the access layer to the distribution layer,
between distribution layer switches, between distribution and core layer switches,
and between certain servers or routers and their connected switches. For example,
in Figures 14-1 and 14-14 you can see dual layer 2 connections between the two
distribution layer switches as well as between the distribution and core layer
switches. The problem with this type of design, however, is that it creates layer 2
loops; and with STP running, STP will ensure that only one path is active between
two devices, limiting you to the bandwidth of one of possibly multiple connections.
EtherChannel Overview
An EtherChannel is a layer 2 solution that allows you to aggregate multiple layer
2 Ethernet-based connections between directly connected devices. Basically, an
EtherChannel bundles together multiple Ethernet ports between devices, providing
what appears to be single logical interface. From STP’s perspective, it sees the
EtherChannel as a single logical connection between the connected devices, which
means that you can actually use all of the individual connections, simultaneously, in
the channel you’ve created.
chapter 14 page 462
CCNA® Cisco® Certified
Network Associate
Study Guide
2008 ED
McGraw-Hill