Glossary
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VLAN
Virtual LAN: A group of devices on one or more logically seg-
mented LANs (configured by use of management software), enabling devices
to communicate as if attached to the same physical medium, when they are
actually located on numerous different LAN segments. VLANs are based on
logical instead of physical connections and thus are tremendously flexible.
VLSM
variable-length subnet mask: Helps optimize available address
space and specify a different subnet mask for the same network number on
various subnets. Also commonly referred to as "subnetting a subnet."
VPN
virtual private network: A method of encrypting point-to-point log-
ical connections across a public network, such as the Internet. This allows
secure communications across a public network.
VTP
VLAN Trunk Protocol: Used to update switches in a switch-fabric
about VLANs configured on a VTP server. VTP devices can be a VTP server,
client, or transparent device. Servers update clients. Transparent devices are
only local devices and do not share information with VTP clients. VTPs send
VLAN information down trunked links only.
VTP pruning
VLAN Trunk Protocol is used to communicate VLAN infor-
mation between switches in the same VTP domain. VTP pruning stops
VLAN update information from being sent down trunked links if the
updates are not needed.
WAN
wide area network: A designation used to connect LANs together
across a DCE (data communications equipment) network. Typically, a
WAN is a leased line or dial-up connection across a PSTN network. Exam-
ples of WAN protocols include Frame Relay, PPP, ISDN, and HDLC.
weighted fair queuing
Default queuing method on serial links on all
Cisco routers.
wildcard
Used with access-list, supernetting, and OSPF configurations.
Wildcards are designations used to identify a range of subnets.
windowing
Flow-control method used with TCP at the Transport layer of
the OSI model.
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