Connectivity Fault Management Support for EVPN and Layer 2 VPN Overview
The IEEE 802.1ag specification provides for Ethernet connectivity fault management (CFM). The goal of CFM is to monitor an Ethernet network that consists of one or more service instances through the use of CFM protocol messages. CFM partitions the service network into various administrative domains. Each administrative domain is mapped into a maintenance domain. A maintenance association end point (MEP) refers to the boundary of a domain. A MEP generates and responds to CFM protocol messages. You can configure multiple up (PE to PE) MEPs or down (PE to CE) MEPs for a single instance of a maintenance domain identifier and a maintenance association name to monitor services in a VPN.
For Layer 2 VPNs and EVPN networks, you can configure multiple up MEPs for a single combination of maintenance association ID and maintenance domain ID on a routing instance on the logical interfaces (IFLs), regardless of whether the logical interface is composed of physical interfaces on the same device or on different devices. The devices must be in enhanced IP network services mode.
In an EVPN network, the following CFM features are supported:
Monitoring the connectivity between two provider edge (PE) routers in an active-active or active-standby multihomed configuration.
Delay measurement and Synthetic Loss measurement. This feature is not supported when multiple MEPs are configured on multiple logical interfaces (IFLs) on the same physical interface (IFD).
CFM monitoring between PE devices and customer edge (CE) devices. When the customer edge device is not a Juniper Networks device, you can enable CFM monitoring by using either the remote defect indication (RDI) bit or the Interface Status TLV. For more information, see Understanding CFM Monitoring between CE and PE Devices
Starting with 18.3R1, Junos OS supports CFM configuration in attachment circuits (AC) on EVPN with ETREE services. The AC is a physical or virtual circuit that connects a CE device to a PE device. You can configure multiple Up MEPs on the MD or MA to monitor each AC between the CE and PE.
Starting with 18.3R1, Junos OS supports maintenance intermediate points (MIPs) on Attachment Circuits on EVPN with ETREE and EVPN with ELAN services. When you configure MIP using the named bridge domain, all the interfaces will be enabled except for the EVPN core interface. For more information on MIPS, see Configuring Maintenance Intermediate Points (MIPs).
Starting with 19.2R1, Junos OS supports MEPs and MIPs on ACs in an EVPN-VPWS network. CFM monitoring on EVPN-VPWS supports continuity check messages (CCM), delay measurements, synthetic loss measurement, loopback and link trace messages on single-active multihomed networks.
Starting in Junos OS Release 20.2R1, Junos OS supports inline performance monitoring on an EVPN network. When inline performance monitoring is enabled, the router offloads performance monitoring packet processing from the CPU to other hardware, thereby decreasing the load on the CPU and allowing an increase in the number of performance monitoring session. Inline performance monitor only applies to delay measurements (DM) and synthetic loss measurements (SLM).
For more information on inline performance monitoring, see Enabling Inline Mode Of Performance Monitoring To Achieve Maximum Scaling.
For more information on configuring delay measurment, see Configuring Ethernet Frame Delay Measurement Sessions.
For more information on configuring synthetic loss measurement, see Configuring Ethernet Synthetic Loss Measurements.
LImitations of CFM on layer 2 VPN and EVPNs
In a circuit cross-connect (ccc) layer 2 VPN or local switch with MEPs and maintenance intermediate points (MIPs), the counter for link trace messages (LTMs) received on the MAC address of the up MEP does not get incremented when the MIP in the path is configured at the same level. The MIP traps the LTM packet, while the LTR message is sent. This leads to a discrepancy between the number of LTMs received and the number of LTRs sent.
CFM up MEP on an EVPN network does not support the use of action profiles for interface down. In other words, you can configure an action profile, but no action is taken.
CFM up MEP is supported on EVPN with ELAN and EVPN with ETREE services.
CFM monitoring between leaf nodes on EVPN with ETREE services is not supported. CFM monitors MEP session from a leaf node to a root node and from a root node to another root node.
CFM monitors the AC connectivity from between PE devices, learning about local adjacencies. In EVPN with E-TREE services, performance monitoring on local adjacencies is not supported.
For more information on CFM, see IEEE 802.1ag OAM Connectivity Fault Management Overview.