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5-8 CHAPTER 5: VIRTUAL LANS (VLANS)
In Figure 5-4 and Figure 5-5:
■ 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 into 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.
Spanning Tree Protocol (STP) Bridge Protocol Data Unit (BPDU) traffic is
always untagged and occurs on all ports when Spanning Tree is
enabled.
For the purposes of VLAN classification, packets arriving on a port with
an 802.1Q tag containing a vlanid of 0 are treated as untagged.
Mixing Port-based and Tagged VLANs
You can configure the Switch 3800 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 and multiple tag-based VLANs.
Protocol-based
VLANs
Protocol-based VLANs enable you to define a protocol filter that the
Switch 3800 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 5-6, the hosts are running both the IP and NetBIOS protocols.
SW3800.BK Page 8 Tuesday, May 5, 1998 5:20 PM