Allied Telesis AT-S100 - Manual (Page 67)

AT-S100 Management Software User’s Guide
67
The syntax of this command is:
spanning-tree portfast bpdu-guard default
The following commands enable the BPDU Guard feature on a bridge:
switch#configure terminal
switch(config)#spanning-tree portfast bpdu-guard
For more information about this command, see “SPANNING-TREE
PORTFAST BPDU-GUARD DEFAULT” on page 254.
Configuring
802.1p Class of
Service
When a port on an Ethernet switch becomes oversubscribed—its egress
queues contain more packets than the port can handle in a timely
manner—the port may be forced to delay the transmission of some
packets, resulting in the delay of packets reaching their destinations. A
port may be forced to delay transmission of packets while it handles other
traffic. Some packets destined to be forwarded to an oversubscribed port
from other switch ports may be discarded.
Although minor delays are often of no consequence to a network or its
performance, there are applications, referred to as delay or time sensitive
applications, that can be impacted by packet delays. Voice transmission
and video conferencing are two examples. A delay in the transmission of
packets carrying their data could impact the quality of the audio or video.
This is where CoS can be of value. What it does is it permits a switch to
give higher priority to some packets over other packets.
There are two principal types of traffic found on the ports of a Gigabit
Ethernet switch, one being untagged packets and the other tagged
packets. As explained in “Tagged VLAN Overview” on page 257, one of
the principal differences between them is that tagged packets contain
VLAN information.
CoS applies mainly to tagged packets because, in addition to carrying
VLAN information, these packets can also contain a priority level
specifying how important (delay sensitive) a packet is in comparison to
other packets. It is this number that the switch refers to when determining
a packet’s priority level.
The 802.1p Class of Service (CoS) feature is configured on a per port
basis. The following examples show how to set this feature.
To assign a CoS ingress value to port 18 with a user-priority of 4, use the
following commands:
switch# configure terminal