Allied Telesis 2.6.1 manual Generic Vlan Registration Protocol Gvrp, Layer 2 Switching Process

80 AT-8800 Series Switch User Guide

Generic VLAN Registration Protocol (GVRP)

The GARP application GVRP allows switches in a network to dynamically share VLAN membership information, to reduce the need for statically configuring all VLAN membership changes on all switches in a network. See the Generic Attribute Registration Protocol (GARP) chapter in the Rapier Switch Software Reference.

Layer 2 Switching Process

The Layer 2 switching process comprises related but separate processes. The Ingress Rules admit or discard frames based on their VLAN tagging. The Learning Process learns the MAC addresses and VLAN membership of frames admitted on each port. The Forwarding Process determines which ports the frames are forwarded to, and the Quality of Service priority with which they are transmitted. Finally, the Egress Rules determine for each frame whether VLAN tags are included in the Ethernet frames that are transmitted. These processes assume that each station on the extended LAN has a unique data link layer address, and that all data link layer frames have a header which includes the source (sender’s) MAC address and destination (recipient’s) MAC address.

The Ingress Rules

When a frame first arrives at a port, the Ingress Rules for the port check the VLAN tagging in the frame to determine whether it will be discarded or forwarded to the Learning Process.

The first check depends on whether the Acceptable Frame Types parameter is set to Admit All Frames or to Admit Only VLAN Tagged Frames. A port that transmits only VLAN tagged frames, regardless of which VLAN the port belongs to, will be automatically set to Admit Only VLAN Tagged Frames. The user cannot change this setting. Frames with a null numerical VLAN Identifier (VID) are VLAN-untagged frames, or frames with priority tagging only.

Every frame received by the switch must be associated with a VLAN. If a frame is admitted by the Acceptable Frame Types parameter, the second part of the Ingress Rules associates each untagged frame admitted with the VID of the VLAN for which the port is untagged.

Every port belongs to one or more VLANs, and therefore every incoming frame will have a VID to show which VLAN it belongs to. The final part of the Ingress Rules depends on whether Ingress Filtering is enabled for the port. If Ingress Filtering is disabled, all frames are passed on to the Learning Process, regardless of which VLAN they belong to. If Ingress Filtering is enabled, frames are admitted only if they have the VID of a VLAN to which the port belongs. If they have the VID of a VLAN to which the port does not belong, they are discarded.

Software Release 2.6.1 C613-02039-00 REV A