3Com Switch 4200G Configuration Guide

68 CHAPTER 14: BASIC PORT CONFIGURATION
Configuring the Default
VLAN ID for an Ethernet
Port
An access port can belong to only one VLAN. Therefore, the VLAN an access port
belongs to is also the default VLAN of the access port. A hybrid/trunk port can belong
to several VLANs, and so a default VLAN ID for the port is required.
■ After you configure default VLAN IDs for Ethernet ports, the packets passing
through the ports are processed in different ways depending on different
situations:
CAUTION:
To guarantee the proper packet forwarding, the default VLAN ID of the local hybrid
port or trunk port should be identical with that of the hybrid port or trunk port on the
peer switch.
Adding an Ethernet Port
to Specified VLANs
You can add the specified Ethernet port to a specified VLAN. After that, the Ethernet
port can forward the packets of the specified VLAN, so that the VLAN on this switch
can intercommunicate with the same VLAN on the peer switch.
An access port can only be added to one VLAN, while hybrid and trunk ports can be
added to multiple VLANs.
Note that the port shall be added to an existing VLAN.
Table 46 Processing of incoming/outgoing packet
Port
type
Processing of an incoming packet
Processing of an outgoing packet
If the
packet
does not
carry a
VLAN tag
If the packet carries a VLAN
tag
Access Receive the
packet and
add the
default tag
to the
packet.
If the VLAN ID is just the default
VLAN ID, receive the packet.
If the VLAN ID is not the default
VLAN ID, discard the packet.
Deprive the tag from the packet and
send the packet.
Trunk If the VLAN ID is just the default
VLAN ID, receive the packet.
If the VLAN ID is not the default
VLAN ID but is one of the VLAN
IDs allowed to pass through the
port, receive the packet.
If the VLAN ID is neither the
default VLAN ID, nor one of the
VLAN IDs allowed to pass
through the port, discard the
packet.
If the VLAN ID is just the default
VLAN ID, deprive the tag and send
the packet.
If the VLAN ID is not the default
VLAN ID, keep the original tag
unchanged and send the packet.
Hybrid If the VLAN ID is just the default
VLAN ID, deprive the tag and send
the packet.
If the VLAN ID is not the default
VLAN ID, deprive the tag or keep the
tag unchanged (whichever is done is
determined by the port hybrid vlan
vlan-id-list { tagged | untagged }
command) and send the packet.