CompTIA® Network+ : Vlan &
Common Tcp And Udp Default Ports
VLAN - Virtual Local Area Networks:
VLAN derives it's name from the fact that there is only
one physical network, but two or more logical networks.
A VLAN may be created by any of these methods:
VLAN by port association - Membership in a VLAN can
be defined based on the ports that belong to the VLAN.
For example, in a bridge with four ports, ports 1, 2,
and 4 belong to VLAN 1 and port 3 belongs to VLAN 2.
The main disadvantage of this method is that it does
not allow for user mobility. If a user moves to a different
location away from the assigned bridge, the network
manager must reconfigure the VLAN.
VLAN by MAC address association: Here, membership
in a VLAN is based on the MAC address of the workstation.
The switch tracks the MAC addresses which belong to
each VLAN (see Figure4). Since MAC addresses form a
part of the workstation's network interface card, when
a workstation is moved, no reconfiguration is needed
to allow the workstation to remain in the same VLAN.
This is unlike Layer 1 VLAN's where membership tables
must be reconfigured. The main problem with this method
is that VLAN membership must be assigned initially.
In networks with thousands of users, this is no easy
task. Also, in environments where notebook PC's are
used, the MAC address is associated with the docking
station and not with the notebook PC. Consequently,
when a notebook PC is moved to a different docking station,
its VLAN membership must be reconfigured.
VLANs by Protocol Type - VLAN membership for Layer
2 VLAN's can also be based on the protocol type field
found in the Layer 2 header. For example, VLANs that
carry only IP traffic and those that carry only IPX
traffic. However this type of VLANs are not popular.
VLANs by IP subnet address - Membership is based
on the Layer 3 header. The network IP subnet address
can be used to classify VLAN membership. Although VLAN
membership is based on Layer 3 information, this has
nothing to do with network routing and should not be
confused with router functions. In this method, IP addresses
are used only as a mapping to determine membership in
VLAN's. No other processing of IP addresses is done.
In Layer 3 VLAN's, users can move their workstations
without reconfiguring their network addresses. The only
problem is that it generally takes longer to forward
packets using Layer 3 information than using MAC addresses.
This is the most widely used VLAN type.
The 802.1Q draft standard defines Layer 1 and Layer 2
The following are the important terms associated with
VLAN 1 is the management VLAN.
Static VLAN : VLAN is statically assigned to the
physical port and never changes.
Dynamic VLAN : VMPS automatically assigns VLAN based
Access Link : An access link can carry only one VLAN
(used between host and switch port)
Trunk Link : A trunk link can carry multiple VLANs.
Used to connect to other switches, routers, or servers
Two types of Trunk framing: ISL (Cisco only) and