Table Of Contents
CFM Support on Customer VLANs
First Published: April 19, 2010Last Updated: February 13, 2011
CFM support on a customer VLAN (C-VLAN) allows a customer to provision maintenance intermediate points (MIPs) and Up maintenance endpoints (MEPs) on a C-VLAN component for dot1q-tunnel ports, selective Q-in-Q (QnQ) ports, and 802.1ad C-UNI (1:2 VLAN mapping) ports. MIPs and Up MEPs provide a customer with visibility to network traffic on the C-VLAN. CFM support on a C-VLAN also provides a common point for service verification and standardizes the user-network interface (UNI).
This document describes the CFM Support on C-VLANs feature, an enhancement to the current IEEE CFM implementation in Cisco IOS software.
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 CFM Support on C-VLANs" section.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for CFM Support on C-VLANs
•The CFM 8.1ag module must be present in the software image.
Restrictions for CFM Support on C-VLANs
•CFM support on C-VLANs is supported only in the IEEE CFM protocol.
•CFM support on C-VLANs is supported only on switch ports.
•A port must be configured to tunnel from a C-VLAN into a service provider (S-VLAN); otherwise, the C-VLAN MEP configured for that service is inactive and does not process CFM messages. The C-VLAN MEP can still be configured but it is inactive.
•Down MEPs in a C-VLAN component can be configured but are always inactive.
•Autocreation of MIPs on C-VLANs is not supported.
•CFM is transparent if it is configured on a physical interface where cross-connect is configured.
Information About CFM Support on C-VLANs
Dot1q Tunnel and Selective QnQ Interfaces
A dot1q-tunnel or selective QnQ interface represents a demarcation point between a C-VLAN space and an S-VLAN space. For purposes of CFM protocol processing, a dot1q-tunnel port is modeled as having two components: a C-VLAN component and an S- VLAN component. The C-VLAN component processes double-tagged packets from the relay-function and single-tagged packets from the wire. The S-VLAN component processes single-tagged packets from the relay-function and untagged packets from the wire.
CFM traffic belonging to each of the C-VLAN and S-VLAN components can be distinguished based on Ethernet layer encapsulation. This distinction allows each of the components to use the entire maintenance level range (0 to 7) without violating the maintenance domain hierarchy.
The CFM traffic generated by the C-VLAN component is transparent to the S-VLAN component if the maintenance levels of the C- VLAN component are lower than those of the S-VLAN component. The Ethernet encapsulation should be used in combination with the CFM maintenance level to determine which maintenance domain a particular traffic flow belongs to.
CFM Support on C-VLANs
The current implementation of IEEE CFM for switch ports in Cisco IOS software provides for the provisioning of maintenance points only on S-VLANs; customers cannot monitor or troubleshoot their networks if they are provisioned on provider edge (PE) devices as aggregation nodes supporting QnQ or 802.1ad services. Double-tagged CFM frames going into a dot1q-tunnel port either from the wire or from the relay-function are transparently forwarded; thus, customers cannot create C-VLAN maintenance points on the PE bridge.
The CFM Support on C-VLANs feature enhances the current IEEE CFM implementation in Cisco IOS software by allowing customers to provision MIPs and Up MEPs on the C-VLAN component and adds support for a new service type, ECFM_SERVICE_CVLAN.
The two sections that follow describe the CFM functions of the S-VLAN and C-VLAN components with the CFM Support on C-VLANs feature implemented.
S-VLAN Component with CFM Support on C-VLANs
With the CFM Support on C-VLANs feature implemented, the S-VLAN component supports the following functions and attributes:
•Up MEPs at any level (0 to 7).
•All MEPs use the port's access VLAN (the outer tag or S-VLAN).
•CFM frames transmitted and received by Up MEPs have a single VLAN tag (the Ethertype may be dot1q or dot1ad), and the VID is equal to the port's access VLAN (S-VLAN).
The reason for this configuration is that the dot1q-tunnel interface marks the endpoint of the S-VLAN domain; hence, its associated S-VLAN component should mark the endpoint of the CFM domain running over the S-VLAN space.
C-VLAN Component with CFM Support on C-VLANs
With the CFM Support on C-VLANs feature implemented, the C-VLAN component supports the following functions and attributes:
•MIPs at any maintenance level (0 to 7).
•MIPs process CFM frames that are single-tagged when they come from the wire and double-tagged when they come from the relay-function.
•Transparent point functions.
•Up MEPs at any maintenance level (0 to 7).
•Up MEPs use a stack of two tags: an outer tag with a VID equal to the port's access VLAN (S-VLAN) and an inner tag with a selected C-VLAN that is allowed through the dot1q-tunnel port.
Note CFM frames transmitted and received by Up MEPs are always double-tagged.
IEEE Standard for Local and Metropolitan Area Networks Virtual Bridged Local Area Networks
MIB MIBs Link
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Feature Information for CFM Support on C-VLANs
Table 1 lists the release history for this feature.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which 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 software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
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