Restrictions And Limitations For Frame Relay Pvc Oversubscription; Virtual Lan Oversubscription; Feature History For Vlan Oversubscription; Restrictions And Limitations For Vlan Oversubscription - Cisco 10000 Series Configuration Manual

Chapter 15 Oversubscribing Physical and Virtual Links

Restrictions and Limitations for Frame Relay PVC Oversubscription

If customers concurrently use all of the network capacity, congestion can occur. However, the risk of
congestion is low if you do not oversubscribe too much and if you avoid oversubscribing networks that
are likely to congest.

Virtual LAN Oversubscription

The Cisco 10000 series router supports the oversubscription of IEEE 802.1Q virtual LANs (VLANs) to
improve network utilization of otherwise underutilized shared networks by leveraging statistical
multiplexing on 802.1Q networks. Because of the bursty nature of LAN traffic and the typical low
utilization of Ethernet at the network edge, oversubscription is an appropriate solution for eliminating
unused bandwidth on Ethernet networks.
Oversubscription enables you to configure a total committed information rate (CIR) for a particular
VLAN that is greater than the speed of the interface. Because different users require high bandwidth
utilization at different times, service providers can oversubscribe network ports to provide services to
more users and improve network utilization.
Network congestion is a concern, especially when oversubscribing connections. In some circumstances,
the aggregate bandwidth might exceed capacity; however, the implementation of oversubscription
guarantees minimum quality of service and fair treatment of all users. When packet drop is required,
Ethernet's congestion avoidance and congestion management mechanisms as well as the
oversubscription logic ensure that packet drops affect lower priority traffic first.
The PRE3 allows the aggregate rate of all VLANs created on an interface to exceed the available
bandwidth. The excess bandwidth is distributed among the VLANs proportionally to their weights using
the shape parent and child policies applied on the subinterface. For more information, see the
"Distribution of Remaining Bandwidth Using Ratio" section on page

Feature History for VLAN Oversubscription

Cisco IOS Release
Release 12.3(7)XI1
Release 12.2(28)SB
Release 12.2(31)SB2

Restrictions and Limitations for VLAN Oversubscription

In some circumstances, the aggregate bandwidth might exceed capacity. However, the implementation
of oversubscription guarantees minimum quality of service and fair treatment of all users.
OL-7433-09
Description
The VLAN oversubscription feature was introduced on the
PRE2.
This feature was integrated in Cisco IOS
Release 12.2(28)SB for the PRE2.
This feature was introduced on the PRE3 to allow
aggregate VLAN rates to exceed the available bandwidth.
Cisco 10000 Series Router Quality of Service Configuration Guide
Virtual LAN Oversubscription
5-14.
Required PRE
PRE2
PRE2
PRE3
15-9