802.3ah OAM

802.3ah Clause 57 (efm-oam) defines the Operations, Administration, and Maintenance (OAM) sublayer, which provides mechanisms useful for monitoring link operation such as remote fault indication and remote loopback control. In general, OAM provides network operators the ability to monitor the health of the network and quickly determine the location of failing links or fault conditions. efm-oam described in this clause provides data link layer mechanisms that complement applications that may reside in higher layers.

OAM information is conveyed in slow protocol frames called OAM protocol data units (OAMPDUs). OAMPDUs contain the appropriate control and status information used to monitor, test and troubleshoot OAM-enabled links. OAMPDUs traverse a single link, being passed between peer OAM entities, and therefore, are not forwarded by MAC clients (like bridges or switches).

The following efm-oam functions are supported:

When the efm-oam protocol fails to negotiate a peer session or encounters a protocol failure following an established session the Port State enters the Link Up condition. This port state is used by many protocols to indicate the port is administratively UP and there is physical connectivity but a protocol, such as efm-oam, has caused the ports operational state to enter a DOWN state. A reason code has been added to help discern if the efm-oam protocol is the underlying reason for the Link Up condition.

show port
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Ports on Slot 1
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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

# show port 1/1/3
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Ethernet Interface
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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

Configured Mode    : access                     Encap Type       : QinQ
Dot1Q Ethertype    : 0x8100                     QinQ Ethertype   : 0x8100
PBB Ethertype      : 0x88e7
Ing. Pool % Rate   : 100                        Egr. Pool % Rate : 100
Ing. Pool Policy   : n/a
Egr. Pool Policy   : n/a
Net. Egr. Queue Pol: default
Egr. Sched. Pol    : n/a
Auto-negotiate     : true                       MDI/MDX          : unknown
Oper Phy-tx-clock  : not-applicable
Accounting Policy  : None                       Collect-stats    : Disabled
Acct Plcy Eth Phys : None                       Collect Eth Phys : Disabled
Egress Rate        : Default                    Ingress Rate     : Default
Load-balance-algo  : Default                    LACP Tunnel      : Disabled

Down-when-looped   : Disabled                   Keep-alive       : 10
Loop Detected      : False                      Retry            : 120
Use Broadcast Addr : False

Sync. Status Msg.  : Disabled                   Rx Quality Level : N/A
Tx DUS/DNU         : Disabled                   Tx Quality Level : N/A
SSM Code Type      : sdh                        ESMC Tunnel      : Disabled

Down On Int. Error : Disabled

CRC Mon SD Thresh  : Disabled                   CRC Mon Window   : 10 seconds
CRC Mon SF Thresh  : Disabled

Configured Address : d8:ef:01:01:00:03
Hardware Address   : d8:ef:01:01:00:03

The operator also has the opportunity to decouple the efm-oam protocol from the port state and operational state. In cases where an operator wants to remove the protocol, monitor the protocol only, migrate, or make changes the ignore-efm-state can be configured in the port>ethernet>efm-oam context. When the ignore-efm-state command is configured on a port the protocol continues as normal. However, any failure in the protocol state machine (discovery, configuration, time-out, loops, and so on) does not impact the port on which the protocol is active and the optional ignore command is configured. There is only a protocol warning message if there are issues with the protocol. The default behavior when this optional command is not configured means the port state is affected by any efm-oam protocol fault or clear conditions. Adding and removing this optional ignore command immediately represents the Port State and Oper State based on the active configuration. For example, if the ignore-efm-state 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. If the ignore-efm-state is removed from a port with an existing efm-oam protocol error, the port transitions to Link UP, Oper Down with the reason code efmOamDown.