Port Traffic Controls
Guaranteed Minimum Bandwidth (GMB)
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.
A queue configured with 0% will be serviced as “strict”.
This means that packets on this queue will be sent until
the queue is empty, before servicing the next lower-
priority queue, regardless of that lower priority queue’s
bandwidth-min setting. If packets are sent to a queue
configured at 0%. lower priority queues can be starved and
not reach their guaranteed minimum bandwidth setting.
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.)
For example, suppose you wanted to configure the following outbound mini-
mum bandwidth availability for ports A1 and A2:
Priority of Minimum Effect on Outbound Bandwidth Allocation
Outbound Bandwidth
Port Queue %
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.
12-16
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