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802.1P CoS Bit Set for PPP and PPPoE Control Frames
First Published: December 4, 2006Last Updated: October 2, 2009
The 802.1P CoS Bit Set for PPP and PPPoE Control Frames feature provides the ability to set user priority bits in the IEEE 802.1Q tagged frame to allow traffic prioritization. This capability enables a way to provide best effort quality of service (QoS) or class of service (CoS) at layer 2 without requiring reservation setup.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for 802.1P CoS Bit Set for PPP and PPPoE Control Frames" section.
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Prerequisites for 802.1P CoS Bit Set for PPP and PPPoE Control Frames
The PPPoE over 802.1Q VLAN feature must be enabled.
Restrictions for 802.1P CoS Bit Set for PPP and PPPoE Control Frames
You cannot set different CoS levels for PPP and PPPoE control packets; all control packets default to a CoS level set at 7.
Information About 802.1P CoS Bit Set for PPP and PPPoE Control Frames
To understand more about the 802.1P CoS Bit Set for PPP and PPPoE Control Frames feature, you should know the following concepts:
Benefits of 802.1P CoS Bit Set for PPP and PPPoE Control Frames
The 802.1P CoS Bit Set for PPP and PPPoE Control Frames feature facilitates moving from ATM-based to Ethernet-based networks by supporting the ability to offer prioritized traffic services, VoIP, and other premium services.
Feature Design of 802.1P CoS Bit Set for PPP and PPPoE Control Frames
The IEEE 802.1P specification is an extension of the IEEE 802.1Q VLANs tagging standard and enables Layer 2 devices to prioritize traffic by using an 802.1P header that includes a three-bit user priority field. Prior to the 802.1P CoS Bit Set for PPP and PPPoE Control Frames feature, PPPoE sessions that were established over 802.1Q VLANs did not make use of the user priority field. If congestion occurs when the 802.1P CoS bit is not set, PPP keepalive packets can be lost, which can result in disconnection of an established session with loss of service to the end user. Congestion caused by noncontrol packets can also prevent new sessions from being established, which can also result in denying service to the end user.
The 802.1P CoS Bit Set for PPP and PPPoE Control Frames feature introduced in Cisco IOS Release 12.2(31)SB supports the ability of Layer 2 devices to prioritize traffic by making use of the priority field of the 802.1P control packets. PPPoE sessions established over 802.1Q VLANs use the priority header field to provide best efforts QoS or CoS at Layer 2 without involving reservation setup. 802.1P traffic is marked and sent to the destination, and no bandwidth reservations are established.
During network congestion, when the Ethernet network and digital subscriber line access multiplexer (DSLAM) offer 802.1P support, control packets are offered a higher priority than noncontrol packets, thereby increasing the likelihood of reliable delivery. PPPoE control packets and PPP packets originating from the broadband remote access server (BRAS) are marked with user priority 7, the highest level of priority.
The following packets are tagged with user priority 7 in their 802.1P header:
–PPPoE Active Discovery Offer (PADO)
–PPPoE Active Discovery Session Confirmation (PADS)
–Link Control Protocol (LCP)
–Network Control Protocol (NCP) (Internet Protocol Control Protocol (IPCP))
How to Configure 802.1P CoS Bit Set for PPP and PPPoE Control Frames
This section contains the following procedures:
Configuring 802.1P CoS Bit Set for PPP and PPPoE Control Frames
The 802.1P CoS Bit Set for PPP and PPPoE Control Frames feature is enabled by default and requires no configuration.
Setting 802.1P Priority Bits for PPPoE Control Frames
Perform this task to set the 802.1P priority bits in 802.1Q frames containing PPP over Ethernet (PPPoE) control packets.
2. configure terminal
3. bba-group pppoe group-name
4. control-packets vlan cos priority
The following command can help troubleshoot 802.1P control frame marking:
•debug pppoe error
Configuration Examples for 802.1P CoS Bit Set for PPP and PPPoE Control Frames
This section provides the following configuration example:
Setting 802.1P Priority Bits for PPPoE Control Frames: Example
The following example shows how to set the 802.1P priority bits in 802.1Q frames containing PPP over Ethernet (PPPoE) control packets:Router> enableRouter# configure terminalRouter(config)# bba-group pppoe group1Router(config-bba-group)# control-packets vlan cos 6
The following sections provide references related to the 802.1P CoS Bit Set for PPP and PPPoE Control Frames feature.
Related Topic Document Title
Broadband access aggregation concepts
Cisco IOS Broadband and DSL Configuration Guide
Broadband access commands
IEEE Standard 802.1P
PPPoE over IEEE 802.1Q
IEEE Standard 802.1Q
Virtual Bridged Local Area Networks
Feature Information for 802.1P CoS Bit Set for PPP and PPPoE Control Frames
Table 1 lists the release history for this feature.
Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.
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