5-8 CHAPTER 5: VIRTUAL LANS (VLANS)In Figure 5-4 and Figure 5-5:n The trunk port on each Switch carries traffic for both VLANMarketing and VLAN Sales.n The trunk port on each Switch is tagged.n The server connected to port 1 on Switch 1 has a NIC that supports802.1Q tagging.n The server connected to port 1 on Switch 1 is a member of bothVLAN Marketing and VLAN Sales.n All other stations use untagged traffic.As data passes into the Switch, the Switch determines if the destinationport requires the frames to be tagged or untagged. All traffic comingfrom and going to the server is tagged. Traffic coming from and goingto the trunk ports is tagged. The traffic that comes from and goes tothe other stations on this network is not tagged.Spanning Tree Protocol (STP) Bridge Protocol Data Unit (BPDU) traffic isalways untagged and occurs on all ports when Spanning Tree isenabled.For the purposes of VLAN classification, packets arriving on a port withan 802.1Q tag containing a vlanid of 0 are treated as untagged.Mixing Port-based and Tagged VLANsYou can configure the Switch 3800 using a combination of port-basedand tagged VLANs. A given port can be a member of multiple VLANs,with the stipulation that only one of its VLANs uses untagged traffic. Inother words, a port can simultaneously be a member of one port-basedVLAN and multiple tag-based VLANs.Protocol-basedVLANsProtocol-based VLANs enable you to define a protocol filter that theSwitch 3800 uses as the matching criteria to determine if a particularpacket belongs to a particular VLAN.Protocol-based VLANs are most often used in situations where networksegments contain hosts running multiple protocols. For example, inFigure 5-6, the hosts are running both the IP and NetBIOS protocols.
