Cisco ASR 920 series, Руководство по настройке Ethernet-маршрутизатора

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From a user ’ s perspective, an interface in loopback mode is in a link-up state.
Cisco Vendor-Specific Extensions
Ethernet OAM allows vendors to extend the protocol by allowing them to create their own type-length-value
(TLV) fields.
OAM Messages
Ethernet OAM messages or OAM PDUs are standard length, untagged Ethernet frames within the normal
frame length bounds of 64 to 1518 bytes. The maximum OAM PDU frame size exchanged between two peers
is negotiated during the discovery phase.
OAM PDUs always have the destination address of slow protocols (0180.c200.0002) and an Ethertype of
8809. OAM PDUs do not go beyond a single hop and have a hard-set maximum transmission rate of 10 OAM
PDUs per second. Some OAM PDU types may be transmitted multiple times to increase the likelihood that
they will be successfully received on a deteriorating link.
Four types of OAM messages are supported:
• Information OAM PDU--A variable-length OAM PDU that is used for discovery. This OAM PDU
includes local, remote, and organization-specific information.
• Event notification OAM PDU--A variable-length OAM PDU that is used for link monitoring. This type
of OAM PDU may be transmitted multiple times to increase the chance of a successful receipt; for
example, in the case of high-bit errors. Event notification OAM PDUs also may include a time stamp
when generated.
• Loopback control OAM PDU--An OAM PDU fixed at 64 bytes in length that is used to enable or disable
the remote loopback command.
• Vendor-specific OAM PDU--A variable-length OAM PDU that allows the addition of vendor-specific
extensions to OAM.
IEEE 802.3ah Link Fault RFI Support
The IEEE 802.3ah Link Fault RFI Support feature provides a per-port configurable option that moves a port
into a blocking state when an OAM PDU control request packet is received with the Link Fault Status flag
set. In the blocking state, the port can continue to receive OAM PDUs, detect remote link status, and
automatically recover when the remote link becomes operational. When an OAM PDU is received with the
Link Fault Status flag set to zero or FALSE, the port is enabled and all VLANs configured on the port are set
to
“ forwarding. ”
If you configure the Ethernet OAM timeout period to be the minimum allowable value of 2 seconds, the
Ethernet OAM session may be dropped briefly when the port transitions from blocked to unblocked. This
action will not occur by default; the default timeout value is 5 seconds. Note
Before the release of the IEEE 802.3ah Link Fault RFI Support feature, when an OAM PDU control request
packet was received with the Link Fault Status flag set, one of three actions was taken:
• A warning message was displayed or logged, and the port remained operational.
Carrier Ethernet Configuration Guide (Cisco ASR 920 Series)
303
Using Ethernet Operations Administration and Maintenance
OAM Messages