Layer 2 Filtering; Ingress Filtering - Allied Telesis SwitchBlade x908 Series Software Reference Manual

Switching Introduction

Layer 2 Filtering

The switch has a forwarding database (also known as the MAC address table) whose entries
determine whether frames are forwarded or discarded over each port. Entries in the
forwarding database are created dynamically by the learning process. A dynamic entry is
automatically deleted from the forwarding database when its ageing timer expires.
The forwarding database supports queries by the forwarding process as to whether frames
with given values of the destination MAC address field should be forwarded to a given port.
For each VLAN, the destination MAC address of a frame to be forwarded is checked against
the forwarding database. If there is no entry for the destination address and VLAN, the frame is
transmitted on all ports in the VLAN that are in the forwarding or disabled state, except the
port on which the frame was received. This process is referred to as flooding. If an entry is
found in the forwarding database but the entry is not marked forwarding or the entry points to
the same port the frame was received on, the frame is discarded. Otherwise, the frame is
transmitted on the port specified by the forwarding database.

Ingress Filtering

The ingress-filter parameter of the
the
frames entering the specified port (or port range). Each port on the switch belongs to one or
more VLANs. If ingress filtering is enabled, any frame received on the specified port is only
admitted if its VID matches one for which the port is tagged. Any frame received on the port is
discarded if its VID does not match one for which the port is tagged.
Untagged frames are admitted and are assigned the VLAN Identifier (VID) of the port's native
VLAN. Ingress filtering can be turned off by setting the disable parameter of the above two
commands. The default setting of the enable / disable parameter option is enable.
Note:
14.10
switchport mode access command on page
Enabling the vlan-disable parameter of the
also enable ingress filtering, and will override the setting of the switchport mode access, and
trunk commands.
Software Reference for SwitchBlade® x908, x900 and x600 Series Switches
TM
AlliedWare Plus Operating System - Software Version 5.3.1
switchport mode trunk command on page 17.11
17.9, enables or disables ingress filtering of
thrash-limiting command on page 15.44
and
will
C613-50007-01 REV B