Cisco ASR 920 series Configuration Guide Ethernet Router

Benefits of Transparent CFM
The current implementation of IEEE 802.1ag CFM for EVC infrastructure 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.
The Transparent CFM support enhances the current IEEE CFM implementation by allowing customers to
monitor the network at any level (0-7); CFM frames with single tag from the customer end and double tagged
frames from network end are forwarded transparently.
S-VLAN Component with Transparent CFM Support
With the Transparent CFM support implemented, the S-VLAN component supports the following functions
and attributes:
•
Up MEPs at any level (0 to 7).
•
All MEP uses the S-VLAN for processing.
•
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 Transparent CFM Support on C-VLANs
With the Transparent 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).
•
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.
Prerequisites for Transparent CFM
•
The CFM 802.1ag module must be present in the software image.
Restrictions for Transparent CFM
•
Untagged encapsulation is not supported for transparent CFM.
•
Transparent CFM is not supported on Smart SFP.
Carrier Ethernet Configuration Guide (Cisco ASR 920 Series)
66
Transparent CFM
Benefits of Transparent CFM

Cisco ASR 920 series Specifications

General

Brand	Cisco
Model	ASR 920 series
Category	Network Router
Language	English