29. Virtual LANs
ROX™ v2.2 User Guide
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RuggedBackbone™ RX1500
Frames transmitted out of the port on all VLANs other than the port’s native VLAN are always sent
tagged.
Sometimes it may be desirable to manually restrict the traffic on the trunk to a specified
group of VLANs; for example, when the trunk connects to a device, such as a Layer 3
router, that supports a subset of the available VLANs. To prevent the trunk port from being
a member of the VLAN, include it in the VLAN’s Forbidden Ports list.
Port Type
VLANs Supported
PVID Format
Usage
Untagged
VLAN Unaware networks – All frames are sent and received
without the need for VLAN tags.
Edge
1 (Native)
Configured
Tagged
VLAN Aware networks – VLAN traffic domains are enforced
on a single VLAN.
Trunk
All Configured
Tagged or
Untagged
Switch-to-Switch connections – VLANs must be manually
created and administered or can be dynamically learned
through GVRP.
Multiple-VLAN end devices – Implement connections to end
devices that support multiple VLANs at the same time.
Table 29.1. Port Types
29.1.5. VLAN Ingress and Egress Rules
Ingress Rules
The VLAN ingress rules are applied to all frames when they are received by the switch:
Frame received
This does not depend on ingress port’s VLAN
configuration parameters
Untagged
Priority
Tagged (VID=0)
Tagged
(valid VID)
VLAN ID associated with the frame
PVID
PVID
VID in the tag
Frame dropped due to its tagged/untagged format
No
No
No
Frame dropped, if frame 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 is associated with
N/A
N/A
No
Table 29.2. Ingress Rules
Egress Rules
The VLAN egress rules are applied to all frames when they are transmitted by the switch:
Frame sent
On other VLAN
Egress port type
On egress port’s
native VLAN
Port is a member
of the VLAN
Port is not a
member of the VLAN
Edge
N/A (frame is dropped)
Trunk
According to the egress port’s
“PVID Format” parameter
Tagged
dropped
Table 29.3. Egress Rules
29.1.6. Forbidden Ports List
Each VLAN can be configured to exclude ports from membership in the VLAN.
29.1.7. VLAN-aware Mode of Operation
The native operation mode for an IEEE 802.1Q compliant switch is VLAN-aware. Even if a specific
network architecture does not use VLANs, ROX™ default VLAN settings allow the switch still to