3Com 3CBLSG48 User Manual page 118

C C VLANS 107
HAPTER 8: ONFIGURING
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 be-
tween 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 re-
mains 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 anoth-
er 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.