802.3ah Clause 57 (EFM OAM) defines the Operations, Administration, and Maintenance (OAM) sublayer, which is a link level Ethernet OAM. It provides mechanisms for monitoring link operations such as remote fault indication and remote loopback control.
Ethernet OAM gives network operators the ability to monitor the status of Ethernet links and quickly determine the location of failing links or fault conditions.
Because some of the sites where the 7705 SAR will be deployed will only have Ethernet uplinks, this OAM functionality is mandatory. For example, mobile operators must be able to request remote loopbacks from the peer router at the Ethernet layer in order to debug any connectivity issues. EFM OAM provides this capability.
EFM OAM is supported on network and access Ethernet ports and is configured at the port level. The access ports can be configured to tunnel the OAM traffic originated by the far-end devices.
EFM OAM has the following characteristics.
All EFM OAM, including loopbacks, operate on point-to-point links only.
EFM loopbacks are always line loopbacks (line Rx to line Tx).
When a port is in loopback, all frames (except EFM frames) are discarded. If dynamic signaling and routing is used (dynamic LSPs, OSPF, IS-IS, or BGP routing), all services also go down. If all signaling and routing protocols are static (static routes, LSPs, and service labels), the frames are discarded but services stay up.
The following EFM OAM functions are supported:
OAM capability discovery
configurable transmit interval with an Information OAMPDU
active or passive mode
OAM loopback
OAMPDU tunneling and termination (for Epipe service)
dying gasp at network and access ports
non-zero vendor-specific information field — the 32-bit field is encoded using the format 00:PP:CC:CC and references TIMETRA-CHASSIS-MIB
00 — must be zeros
PP — the platform type from tmnxHwEquippedPlatform
CC:CC — the chassis type index value from tmnxChassisType that is indexed in tmnxChassisTypeTable. The table identifies the specific chassis backplane.
The value 00:00:00:00 is sent for all releases that do not support the non-zero value or are unable to identify the required elements. There is no decoding of the peer or local vendor information fields on the network element. The hexadecimal value is included in the show port port-id ethernet efm-oam output.
With ignore-efm-state configured, if the EFM OAM protocol cannot negotiate a peer session or an established session fails, the port will enter the link up state. The link up state is used by many protocols to indicate that the port is administratively up and there is physical connectivity but a protocol (such as EFM OAM) has caused the port operational state to be down. The show port slot/mda/port command output includes a Reason Down field to indicate if the protocol is the underlying reason for the link up state. For EFM OAM, the Reason Down code is efmOamDown. This is shown in the following command output example, where port 1/1/3 is in a link up state.
*A:ALU-1># show port
===============================================================================
Ports on Slot 1
===============================================================================
Port Admin Link Port Cfg Oper LAG/ Port Port Port C/QS/S/XFP/
Id State State MTU MTU Bndl Mode Encp Type MDIMDX
-------------------------------------------------------------------------------
1/1/1 Down No Down 1578 1578 - netw null xcme
1/1/2 Down No Down 1578 1578 - netw null xcme
1/1/3 Up Yes Link Up 1522 1522 - accs qinq xcme
1/1/4 Down No Down 1578 1578 - netw null xcme
1/1/5 Down No Down 1578 1578 - netw null xcme
1/1/6 Down No Down 1578 1578 - netw null xcme
*A:ALU-1># show port 1/1/3
===============================================================================
Ethernet Interface
===============================================================================
Description : 10/100/Gig Ethernet SFP
Interface : 1/1/3 Oper Speed : N/A
Link-level : Ethernet Config Speed : 1 Gbps
Admin State : up Oper Duplex : N/A
Oper State : down Config Duplex : full
Reason Down : efmOamDown
Physical Link : Yes MTU : 1522
Single Fiber Mode : No Min Frame Length : 64 Bytes
IfIndex : 35749888 Hold time up : 0 seconds
Last State Change : 12/18/2012 15:58:29 Hold time down : 0 seconds
Last Cleared Time : N/A DDM Events : Enabled
Phys State Chng Cnt: 1
......
The EFM OAM protocol can be decoupled from the port state and operational state. In cases where an operator wants to remove the protocol, monitor only the protocol, migrate, or make changes, the ignore-efm-state command can be configured under the config>port>ethernet>efm-oam context.
When the ignore-efm-state command is configured on a port, the protocol behavior is normal. However, any failure in the EFM protocol state (discovery, configuration, time-out, loops, and so on) will not affect the port. Only a protocol warning message will be raised to indicate issues with the protocol. When the ignore-efm-state command is not configured on a port, the default behavior is that the port state will be affected by any EFM OAM protocol fault or clear conditions.
Enabling and disabling this command will immediately affect the port state and operating state based on the active configuration, and this will be displayed in the show port command output. For example, if the ignore-efm-state command is configured on a port that is exhibiting a protocol error, that protocol error does not affect the port state or operational state and there is no Reason Down code in the output. If the ignore-efm-state command is disabled on a port with an existing EFM OAM protocol error, the port will transition to port state link up, operational state down with reason code efmOamDown.
If the port is a member of a microwave link, the ignore-efm-state command must be enabled before the EFM OAM protocol can be activated. This restriction is required because EFM OAM is not compatible with microwave links.