GMB provides a method for ensuring that each of a given port's outbound traffic priority queues has a specified minimum consideration for sending traffic out on the link to another device. This can prevent a condition where applications generating lower-priority traffic in the network are frequently or continually "starved" by high volumes of higher-priority traffic. You can configure GMB per-port and, in the case of the HP 2920, 3800, and 5400R switches, per static trunk.
For any port, group of ports or (for the 2920, 3800, or 5400R switches), static trunks, you can use the default minimum bandwidth settings for each outbound priority queue or a customized bandwidth profile. It is also possible to disable the feature entirely.
The switch services per-port outbound traffic in a descending order of priority; that is, from the highest priority to the lowest priority. By default, each port (including each port in a static trunk) offers eight prioritized, outbound traffic queues. Tagged VLAN traffic is prioritized according to the 802.1p priority the traffic carries. Untagged VLAN traffic is assigned a priority of 0 (normal).
Per-port outbound priority queues
| 802.1p Priority settings in tagged VLAN packets[a] | Outbound priority queue for a given port |
|---|---|
| 1 (low) | 1 |
| 2 (low) | 2 |
| 0 (normal) | 3 |
| 3 (normal) | 4 |
| 4 (medium) | 5 |
| 5 (medium) | 6 |
| 6 (high) | 7 |
| 7 (high) | 8 |
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[a] The switch processes outbound traffic from an untagged port at the "0" (normal) priority level. |
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You can use GMB to reserve a specific percentage of each port's available outbound bandwidth for each of the eight priority queues. This means that regardless of the amount of high-priority outbound traffic on a port (including each port in a static trunk), you can ensure that there will always be bandwidth reserved for lower-priority traffic.
Since the switch services outbound traffic according to priority (highest to lowest), the highest-priority outbound traffic on a given port automatically receives the first priority in servicing. Thus, in most applications, it is necessary only to specify the minimum bandwidth you want to allocate to the lower priority queues. In this case, the high-priority traffic automatically receives all unassigned bandwidth without starving the lower-priority queues.
Conversely, configuring a bandwidth minimum on only the high-priority outbound queue of a port or static trunk (and not providing a bandwidth minimum for the lower-priority queues) is not recommended, because it may "starve" the lower-priority queues.
The section Configuring GMB for outbound traffic assumes the ports on the switch offer eight prioritized, outbound traffic queues. This may not always be the case, however, because the switch supports a QoS queue configuration feature that allows you to reduce the number of outbound queues from eight (the default) to four queues, or two.
Changing the number of queues affects the GMB commands (interface bandwidth-min and show bandwidth output) such that they operate only on the number of queues currently configured. If the queues are reconfigured, the guaranteed minimum bandwidth per queue is automatically re-allocated according to the following percentages:
Default GMB percentage allocations per QoS queue configuration
| 802.1p priority | 8 queues (default) | 4 queues | 2 queues |
|---|---|---|---|
| 1 (lowest) | 2% | 10% | 90% |
| 2 | 3% | ||
| 0 (normal) | 30% | 70% | |
| 3 | 10% | ||
| 4 | 10% | 10% | 10% |
| 5 | 10% | ||
| 6 | 15% | 10% | |
| 7 (highest) | 20% |
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![[NOTE: ]](images/note.gif) |
NOTE: For more information on queue configuration and the associated default minimum bandwidth settings, see the chapter "Quality of Service (QoS): Managing Bandwidth More Effectively" in the Advanced Traffic Management Guide for your switch. |
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For any port, group of ports, or static trunk, you can configure either the default minimum bandwidth settings for each outbound priority queue or a customized bandwidth allocation. For most applications, HP recommends configuring GMB with the same values on all ports on the switch so that the outbound traffic profile is consistent for all outbound traffic. However, there may be instances where it may be advantageous to configure special profiles on connections to servers or to the network infrastructure (such as links to routers, other switches, or to the network core).
Syntax:
Configures the default minimum bandwidth allocation for the outbound priority queue for each port or static trunk in the <port-list|trk_#>
The no form of the command disables GMB for all ports and trunks in the <port-list>
You can configure bandwidth minimums from either the global configuration level (as shown above) or from the port or static trunk context level. For information on outbound port queues, see Per-port outbound priority queues.
Syntax:
For ports and trunks in
, specifies the minimum outbound bandwidth as a percent of the total bandwidth for each outbound queue. The queues receive service in descending order of priority of each port.<port-list|trk_#>
NOTE: For application to static trunk interfaces (HP 2920, 3800, and 5400R only), GMB enforcement is applied individually to each port belonging to the trunk, and not to the trunk as a whole.
You must specify a bandwidth percent value for all except the highest priority queue, which may instead be set to "strict" mode. The sum of the bandwidth percentages below the top queue cannot exceed 100%. (0 is a value for a queue percentage setting.)
Configuring a total of less than 100% across the eight queues results in unallocated bandwidth that remains harmlessly unused unless a given queue becomes oversubscribed. In this case, the unallocated bandwidth is apportioned to oversubscribed queues in descending order of priority. For example, if you configure a minimum of 10% for queues 1 to 7 and 0% for queue 8, the unallocated bandwidth is available to all eight queues in the following prioritized order:
Queue 8 (high priority) Queue 7 (high priority) Queue 6 (medium priority) Queue 5 (medium priority) Queue 4 (normal priority) Queue 3 (normal priority) Queue 2 (low priority) Queue 1 (low priority) A setting of 0 (zero percent) on a queue means that no bandwidth minimum is specifically reserved for that queue for each of the ports (including trunked ports) in the
.<port-list|trk_#>Also, there is no benefit to setting the high-priority queue (queue 8) to 0 (zero) unless you want the medium queue (queues 5 and 6) to be able to support traffic bursts above its guaranteed minimum.
[strict]: Provides the ability to configure the highest priority queue asstrict. Per-queue values must be specified in priority order, with queue 1 having the lowest priority and queue 8 (or 4, or 2) having the highest priority (the highest queue is determined by how many queues are configured on the switch. Two, four, and eight queues are permitted (see theqos queue-configcommand). The strict queue is provided all the bandwidth it needs. Any remaining bandwidth is shared among the non-strict queues based on need and configured bandwidth profiles (the profiles are applied to the leftover bandwidth in this case). The total sum of percentages for non-strict queues must not exceed 100.
Example:
For example, suppose you want to configure the following outbound minimum bandwidth availability for ports 1 and 2:
| 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 to 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 GMB of 15% available for outbound traffic. If queue 7 becomes oversubscribed and queue 8 is not already using all of the unallocated bandwidth, 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 GMB 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 GMB 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 GMB 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 GMB 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 GMB 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 GMB of 2% and, if oversubscribed, is subordinate to all the other queues for any unused outbound bandwidth available on the port. |
Either of the following commands configures ports 1 through 5 with bandwidth settings:
HP Switch(config) # int 1-5 bandwidth-min output 2 3 30 10 10 10 15 strict
HP Switch(eth-1-5) # bandwidth-min output 2 3 30 10 10 10 15 strict
This command displays the per-port GMB configuration in the running-config file.
Syntax:
Without
, this command lists the GMB configuration for all ports and static trunks on the switch.<port-list|trk_#>With
, this command lists the GMB configuration for the specified ports and static trunks.<port-list|trk_#>This command operates the same way in any CLI context. If the command lists
for a port or trunk, there are no bandwidth minimums configured for any queue on the port or trunk. (See the description of theDisablednoform of thebandwidth-min outputcommand.)
Listing the GMB configuration displays the GMB configuration resulting from either of the above commands.
Listing the GMB configuration
HP Switch(config)# show bandwidth output 1-5, trk1 Outbound Guaranteed Minimum Bandwidth % Port Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 ------ --- ------ --- ------ --- --- --- ------ 1 2 3 30 10 10 10 15 strict 2 2 3 30 10 10 10 15 strict 3 2 3 30 10 10 10 15 strict 4 2 3 30 10 10 10 15 strict 5 2 3 30 10 10 10 15 strict Trk1 2 3 30 10 10 10 15 strict
Changing the number of queues causes the GMB commands (interface bandwidth-min and show bandwidth output) to operate only on the number of queues currently configured. In addition, when the qos queue-config command is executed, any previously configured bandwidth-min output settings are removed from the startup configuration. For the default GMB percentage allocations per number of queues, see Default GMB percentage allocations per QoS queue configuration.