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LAN Switch Configuration 177
Table 4-14 lists the various types of tagging used by Cisco and the types of interfaces on which
they are used:
The first three options in Table 4-14 are much easier to conceptualize. The frame headers are
encapsulated or modified to reflect a VLAN ID before the frame is sent onto the link between
switches. Before forwarding to the endpoint device, the frame header is changed back to the
original format. With LANE, there is an ATM network between switches. (LANE is a way to
make the ATM network behave like an Ethernet in some ways.) There is no tagging in LANE,
but instead, a different ATM virtual connection is used between the switches for each VLAN.
The virtual connection used implies the VLAN ID.
VLAN Summary
Many benefits can be gained from VLANs, including these:
·
With VLANs, moves, additions, and changes to device connections are easier.
·
By forcing a Layer 3 routing device to be involved between VLANs, greater
administrative control can be used (better accounting, access lists, and so on).
·
Unnecessary LAN bandwidth consumption is reduced compared to a single broadcast
domain.
·
Unnecessary CPU usage is reduced by the resulting reduction in broadcast forwarding.
LAN Switch Configuration
Cisco expects CCNAs to master the concepts behind LAN switching and VLANs. This mastery
includes the ability to configure IOS-based LAN switches using the IOS CLI. This section
outlines the similarities of the switch IOS CLI to the router IOS CLI, as well as contrasting the
commands, syntax, and required configuration elements unique to switches.
Not all Cisco LAN switches provide an IOS CLI interface to the network engineer. Cisco wants
its certifications to prove that the candidate knows the technology and can implement it; that
proof would be onerous if all switch families' user interfaces were required on the CCNA exam.
Table 4-14
Frame Trunking/Tagging Protocols
Tagging Method
Media
Inter-Switch Link (ISL)
Fast Ethernet
802.1Q
Fast Ethernet
802.10
FDDI
LAN Emulation (LANE)
ATM
ch04.fm Page 177 Monday, March 20, 2000 5:02 PM