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<a name="wp1074887"> </a><h1 class="pTitle">
Dynamic Bandwidth Management

</h1>
<a name="wp1073922"> </a><p class="pBody">
On port switching modules where bandwidth is shared, the bandwidth available to each port within a port 
group can be configured based on the port rate mode and speed configurations. Within a port group, some 
ports can be configured in dedicated rate mode while others operate in shared mode.

</p>
<a name="wp1073923"> </a><p class="pBody">
Ports configured in dedicated rate mode are allocated the required bandwidth to sustain a line rate of 
traffic at the maximum configured operating speed, and ports configured in shared mode share the 
available remaining bandwidth within the port group. Bandwidth allocation among the shared mode 
ports is based on the operational speed of the ports. For example, if four ports operating at speeds 1 Gbps, 
1 Gbps, 2 Gbps, and 4 Gbps share bandwidth of 8 Gbps, the ratio of allocation would be 1:1:2:4.

</p>
<a name="wp1073924"> </a><p class="pBody">
Unutilized bandwidth from the dedicated ports is shared among only the shared ports in a port group as 
per the ratio of the configured operating speed. A port cannot be brought up unless the reserved 
bandwidth is quaranteed for the shared ports (see <a href="gen217.html#wp1075218">Table&#160;13-9</a>). For dedicated ports, configured bandwidth 
is taken into consideration while calculating available bandwidth for the port group. This behavior can 
be changed using bandwidth fairness by using the <b class="cBold">rate-mode bandwidth-fairness module </b><em style="font-style: italic; font-weight: normal">number</em> 
command.

</p>
<a name="wp1073928"> </a><p class="pBody">
For example, consider a 48-port 8-Gbps module. This module has 6 ports per port group with 12.8 Gbps 
bandwidth. Ports 3 to 6 are configured at 4 Gbps. If the first port is configured at 8 Gbps dedicated rate 
mode, and the second port is configured at 4-Gbps dedicated rate mode, then no other ports can be 
configured at 4 Gbps or 8 Gbps because the left over bandwidth of 0.8 Gbps (12.8-(8+4)) cannot meet 
the required 0.96 Gbps for the remaining four ports. A minimum of 0.24 Gbps reserved bandwidth is 
required for the for the rest of the four ports. However, if the two ports (for example, 5 and 6) are taken 
out of service (which is not same as shutdown), required reserved bandwidth for the two ports (3 and 4) 
is 0.48 and port 2 can be configured at 4 Gbps in dedicated rate mode. This behavior can be overridden 
by the bandwidth fairness command in which case reserved bandwidth is not enforced. Once the port is 
up, ports 3 and 4 can share the unutilized bandwidth from ports 1 and 2.

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<hr /><br><p class="pBody">Copyright 2010-2013, Cisco Systems, Inc. All rights reserved.</p> 

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