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VLANs
RS400 171 ROS™ v3.5
Frame received
This doesn’t
depend on ingress
port ‘s VLAN configuration
parameters
Untagged
Priority
Tagged
(VID=0)
Tagged
(valid VID)
VLAN the frame associated with PVID PVID VID in the tag
Frame dropped due to its
tagged/untagged format
No No No
Frame dropped, if associated with VLAN
not configured (or learned) in the switch
N/A N/A Yes
Frame dropped, if ingress port is not a
member of the VLAN the frame
associated with
N/A N/A No
Egress Rules
These are the VLAN egress rules, i.e. the rules applied to all frames when they are transmitted
by the switch:
On other
VLAN
Frame sent
Egress port
type
On egress port’s native
VLAN
Port is member
of the VLAN
Port is NOT
member of the
VLAN
Edge N/A (frame is dropped)
Trunk
According to the egress
port’s “PVID Format”
parameter
Tagged dropped
6.1.7 Forbidden Ports List
Each VLAN can be configured to exclude ports from membership in the VLAN.
6.1.8 VLAN-aware and VLAN-unaware operation modes
The native operation mode for an IEEE 802.1Q compliant switch is VLAN-aware. Even if a
specific network architecture doesn’t use VLANs, ROS
TM
default VLAN settings allow the switch
still to operate in a VLAN-aware mode while providing functionality required for almost any
network application. However, the IEEE 802.1Q standard defines a set of rules that must be
followed by all VLAN-aware switches, for example:
• Valid VID range is 1 to 4094 (VID=0 and VID=4095 are invalid)
• Each frame ingressing a VLAN-aware switch is associated with a valid VID
• Each frame egressing a VLAN-aware switch is either untagged or tagged with a valid VID
(this means priority-tagged frames with VID=0 are never sent out by a VLAN-aware switch)
It turns out that some applications have requirements conflicting with the IEEE 802.1Q native
mode of operation (e.g. some applications explicitly require priority-tagged frames to be
received by end devices).