Allied Telesis IE220 Series Manual page 590

VLAN C
OMMANDS
- - -
PORT VLAN FORWARDING PRIORITY
effects on a port would conflict and override each other. Without this command,
each protocol could set a port to forwarding for a VLAN, sometimes overriding the
previous setting by another protocol to block the port. This could sometimes lead
to unexpected broadcast storms.
This command means that, when a protocol is set to have the highest priority over
a data VLAN on a port, it will not allow other protocols to put that port-vlan into a
forwarding state if the highest priority protocol blocked it.
The priority mechanism is only used for blocking-to-forwarding transitions;
protocols remain independent on the forwarding-to-blocking transitions.
For example, consider an EPSR master node in a two-node ESPR ring with the
following settings:
•
•
•
•
•
Initially, the EPSR ring is complete, with port1.0.2 blocking data VLANs vlan20 and
vlan30 and some broadcast traffic flowing through. If the user removes vlan30
from EPSR, a storm is created on vlan30. MAC thrashing protection detects it and
blocks vlan30.
Then after the storm has stopped, MAC thrashing protection sets it to forwarding
again and it keeps oscillating between forwarding and blocking. In the meantime,
the user adds back vlan30 to EPSR as a data VLAN and EPSR blocks it on port1.0.2.
If the priority is set to none (port-vlan-forwarding-priority none), MAC thrashing
protection notices that the storm has stopped again and decides to put vlan30 on
port1.0.2 into forwarding state. This overrides what EPSR requires for this
port-VLAN and creates a storm.
If the priority is set to EPSR or default (port-vlan-forwarding-priority epsr), MAC
thrashing protection notices that the storm has stopped again and attempts to put
vlan30 on port1.0.2 into forwarding state. The higher priority protocol (EPSR) is
blocking the VLAN on this port, so it stays blocking and no storm occurs.
Example To prioritize EPSR over Loop Protection or MAC Thrashing protection settings, so
that Loop Protection or MAC Thrashing protection cannot set a port to the
forwarding state for a VLAN if EPSR has set it to the blocking state, use the
commands:
awplus#
awplus(config)#
C613-50644-01 Rev B
The EPSR master node primary port is configured to switchport interface
port1.0.1
The EPSR master node secondary port is configured to switchport interface
port1.0.2
The EPSR master node control VLAN is configured to VLAN interface vlan10
The EPSR master node has a first data VLAN configured to VLAN interface
vlan20
The EPSR master node has a second data VLAN configured to VLAN interface
vlan30.
configure terminal
port-vlan-forwarding-priority epsr
Command Reference for IE220 Series
AlliedWare Plus™ Operating System - Version 5.5.3-0.x
590