Specifications

8-28 Rapier Switch Software Reference
Software Release 2.7.3
C613-03098-00 REV A
The Ingress Rules
When a frame first arrives at a port, ingress rules for the port check the VLAN
tagging in the frame to determine whether to discard it or forward it 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 is automatically set to Admit Only VLAN
Tagged Frames regardless of the VLAN to which the port belongs. 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. When 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 so every incoming frame has a VID
that shows to which VLAN it belongs. 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 when they have the VID of a VLAN to which the port belongs.
Otherwise, they are discarded.
The default settings for the Ingress Rules are to Admit All Frames, and for
Ingress Filtering to be off. This means that if no VLAN configuration has been
done, all incoming frames pass to the learning process, regardless of whether
not they are VLAN tagged. The parameters for each port’s ingress rules can be
configured by using the command:
set switch port={port-list|all} [acceptable={vlan|all}]
[infiltering={on|off}]
The Learning Process
The learning process uses an adaptive learning algorithm, sometimes called
backward learning, to discover the location of each station on the extended LAN.
All frames admitted by the Ingress Rules on any port are passed on to the
Forwarding Process if they are for destinations within the same VLAN. Frames
destined for other VLANs are passed to the layer three protocol, for instance IP.
For every frame admitted, the frame’s source MAC address and numerical
VLAN Identifier (VID) are compared with entries in the forwarding database
for the VLAN (also known as a MAC address table, or a forwarding table)
maintained by the switch. The forwarding database contains one entry for
every unique station MAC address the switch knows in each VLAN.
If the frame’s source address is not already in the forwarding database for the
VLAN, the address is added and an ageing timer for that entry is started. If the
frame’s source address is already in the forwarding database, the ageing timer
for that entry is restarted. Switch learning is enabled by default; it can be
disabled or enabled by using the commands:
DISable SWItch LEarning
ENAble SWItch LEarning