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C
HAPTER
4: V
IRTUAL
LAN
S
(VLAN
S
)
In Figure 10 and Figure 11:
■
The trunk port on each switch carries traffic for both VLAN
Marketing
and VLAN
Sales
.
■
The trunk port on each switch is tagged.
■
The server connected to port 1 on Switch 1 has a NIC that supports
802.1Q tagging.
■
The server connected to port 1 on Switch 1 is a member of both VLAN
Marketing
and VLAN
Sales
.
■
All other stations use untagged traffic.
As data passes out of the switch, the switch determines if the destination
port requires the frames to be tagged or untagged. All traffic coming
from and going to the server is tagged. Traffic coming from and going to
the trunk ports is tagged. The traffic that comes from and goes to the
other stations on this network is not tagged.
Mixing Port-Based and Tagged VLANs
You can configure the switch using a combination of port-based and
tagged VLANs. A given port can be a member of multiple VLANs, with
the stipulation that only one of its VLANs uses untagged traffic. In other
words, a port can simultaneously be a member of one port-based VLAN,
one specific protocol-based VLAN, and multiple tag-based VLANs.
For the purposes of VLAN classification, packets arriving on a port with an
802.1Q tag containing a VLANid of zero are treated as untagged.
Protocol-Based VLANs
Protocol-based VLANs enable you to define a packet filter that the switch
uses as the matching criteria to determine if a particular packet belongs
to a particular VLAN.
Protocol-based VLANs are most often used in situations where network
segments contain hosts running multiple protocols. For example, in
Figure 12
, the hosts are running both the IP and NetBIOS protocols.
The IP traffic has been divided into two IP subnets, 192.207.35.0 and
192.207.36.0. The subnets are internally routed by the switch. The
subnets are assigned different VLAN names,
Finance
and
Personnel
,
respectively. The remainder of the traffic belongs to the VLAN named
MyCompany
. All ports are members of the VLAN
MyCompany
.