13-24
Port Traffic Controls
Guaranteed Minimum Bandwidth (GMB)
For example, suppose you wanted to configure the following outbound mini-
mum bandwidth availability for ports A1 and A2:
Notes:
Configuring 0% for a queue can result in that
queue being starved if any higher queue becomes over-
subscribed and is then given all unused bandwidth.
The switch applies the bandwidth calculation to the link
speed the port is currently using. For example, if a 10/100
Mbs port negotiates to 10 Mbps on the link, then it bases
its GMB calculations on 10 Mbps; not 100 Mbps.
Use
show bandwidth output <
port-list
>
to display the current
GMB configuration. (The
show config
and
show running
commands do not include GMB configuration data.)
Priority of
Outbound
Port Queue
Minimum
Bandwidth
%
Effect on Outbound Bandwidth Allocation
8
20
Queue 8 has the first priority use of all outbound bandwidth not
specifically allocated to queues 1 - 7. If, for example, bandwidth
allocated to queue 5 is not being used and queues 7 and 8 become
oversubscribed, queue 8 has first-priority use of the unused
bandwidth allocated to queue 5.
7
15
Queue 7 has a guaranteed minimum bandwidth of15% available
for outbound traffic. If queue 7 becomes oversubscribed and
queue 8 is not already using all of the unallocated bandwidth, then
queue 7 can use the unallocated bandwidth. Also, any unused
bandwidth allocated to queues 6 to queue 1 is available to queue
7 if queue 8 has not already claimed it.
6
10
Queue 6 has a guaranteed minimum bandwidth of 10% and, if
oversubscribed, is subordinate to queues 8 and 7 in priority for
any unused outbound bandwidth available on the port.
5
10
Queue 5 has a guaranteed minimum bandwidth of 10% and, if
oversubscribed, is subordinate to queues 8, 7, and 6 for any
unused outbound bandwidth available on the port.
4
10%
Queue 4 has a guaranteed minimum bandwidth of 10% and, if
oversubscribed, is subordinate to queues, 8, 7, 6, and 5 for any
unused outbound bandwidth available on the port.
3
30%
Queue 3 has a guaranteed minimum bandwidth of 30% and, if
oversubscribed, is subordinate to queues, 8, 7, 6, 5, and 4 for any
unused outbound bandwidth available on the port.
2
3%
Queue 2 has a guaranteed minimum bandwidth of 3% and, if
oversubscribed, is subordinate to queues, 8, 7, 6, 5, 4, and 3 for
any unused outbound bandwidth available on the port.
1
2%
Queue 1 has a guaranteed minimum bandwidth of 2% and, if
oversubscribed, is subordinate to all the other queues for any
unused outbound bandwidth available on the port.
3500-5400-6200-8200-MCG-Jan08-K_13_01.book Page 24 Monday, January 28, 2008 10:04 AM