3Com 3CBLSG48 User Guide - Page 118

CHAPTER 8: CONFIGURING VLANS 107 VLANs function at Layer 2. Since VLANs isolate traffic within the VLAN, a Layer 3 router working at a protocol level is required to allow traffic flow between VLANs. Layer 3 routers identify segments and coordinate with VLANs. VLANs are Broadcast and Multicast domains. Broadcast and Multicast traffic is transmitted only in the VLAN in which the traffic is generated. VLAN tagging provides a method of transferring VLAN information between VLAN groups. VLAN1is the default VLAN. All ports are untagged members of VLAN1 by default. If any port becomes an untagged member of a different VLAN, then the port is removed from untagged membership of VLAN1. For example: If port 24 is made an untagged member of VLAN 5, the port will no longer be a member of VLAN1. However, if the port is made an tagged member of VLAN5, it still remains untagged in VLAN1. A port can only be an untagged member of one VLAN. By default it is untagged member of VLAN1. If its untagged membership from another VLAN is removed, it will default to untagged membership in VLAN1. There is no restriction on tagged membership. A port can be a tagged member of any number of multiple VLANs.