OAM as the name suggests stands for Operation, Administration and Management. This feature is mostly used in following areas:
1. Ethernet OAM
2. MPLS OAM
Ethernet OAM - This again has 2 parts:
a. LFM - link fault management which is usually used between direct links. - IEEE 802.3ah
- Failure detection on physical links in both directions, as well as unidirectional failures.
- Ability to put a port in link-loopback mode remotely for diagnostics.
- Report and receive link error events such as framing errors.
https://www.juniper.net/documentation/en_US/junos/topics/concept/lfm-ethernet-oam-ex-series-understanding.html
b. CFM - connectivity fault management which is usually used across the domains. - IEEE 802.1ag
- CFM is used to monitor an Ethernet network at a per-service level, unlike LFM, which functions at the physical link level.
- Fault monitoring using the continuity check protocol. This is a neighbor discovery and health check protocol which discovers and maintains adjacencies at the VLAN or link level.
- Path discovery and fault verification using the linktrace protocol. Similar to IP traceroute, this protocol maps the path taken to a destination MAC address through one or more bridged networks between the source and destination.
- Fault isolation using the loopback protocol. Similar to IP ping, this protocol works with the continuity check protocol during troubleshooting.
CFM can be used at two levels:
- By the service provider to check the connectivity among its provider edge (PE) routers
- By the customer to check the connectivity among its customer edge (CE) routers
https://www.juniper.net/documentation/en_US/junos/topics/concept/layer-2-802-1ag-ethernet-oam-cfm-overview-mx-solutions.html
MPLS OAM - This is nothing but configuring BFD for MPLS LSPs:
https://www.juniper.net/documentation/en_US/junos/topics/usage-guidelines/mpls-configuring-bfd-for-mpls-ipv4-lsps.html
Thanks