The SmartSwitch 2000 Chassis View
2-58 Managing the Hub
Ingress List Operation
A port’s ingress list specifies the VLAN with which received frames will be
associated. The switch’s Filtering Database tracks the associations between VLAN
eligibilities, MAC addresses, and port numbers.
Untagged frames received by an 802.1Q switch port are classified according to the
VLAN membership of the port that receives the frame.
Tagged frames received by an 802.1Q switch port are classified according to the
VLAN indicated in their tag header. A port may receive a tagged frame that
specifies a VLAN other than the one assigned to the port.
Egress List Operation
Each port’s egress list specifies which VLANs are associated with the port, and
specifies what type of frame (tagged or untagged) to transmit for each particular
VLAN on a port. This information may be statically defined by the user, or
dynamically learned and maintained by the switch’s Filtering Database.
If a port receives a tagged frame that specifies a VLAN other than the one
assigned to the port, the switch will dynamically associate that frame’s source
address and VLAN with the port (i.e., add that frame’s VLAN to the receiving
port’s egress list). Dynamically learned VLANs are subject to the same aging rules
as source addresses (e.g., if a tagged frame belonging to a dynamically learned
VLAN is not received by the port within the switch’s aging time, the transmitting
station’s source address and VLAN will be aged out for that port; no unknown
destination frames belonging to the station’s VLAN will be transmitted through
the port until the VLAN is dynamically learned once again). Only tagged frames
can cause the switch to dynamically change a port’s egress list.
802.1Q Port Types
Each 802.1Q switch port is assigned a mode of operation. Port types include:
1Q Trunk
If VLAN membership is to apply to users across several switches, ports used to
connect 802.1Q-aware devices are configured to use 1Q Trunk mode. In this mode,
all frames (except BPDUs) are transmitted with a tag header included in the
frame, allowing VLAN frames to maintain their VLAN ID across multiple
switches. Any untagged frames received by the port are dropped. 1Q Trunk ports
are configured to be members of all VLANs.
1d Trunk
This mode allows a port to transmit to a traditional (802.1d) switch fabric. These
ports transmit only untagged frames, and the switch expects to receive only
untagged traffic through the port. 1d Trunk ports are configured to be members of
all VLANs. This mode can be used to share a connection among multiple VLANs
(e.g., sharing a server between two or more separate VLANs).