Eth-Cfm Frame Format; Figure 10: Eth-Cfm Frame Format - Alcatel-Lucent 7705 Service Manual

ETH-CFM (802.1ag and Y.1731)

ETH-CFM Frame Format

ETH-CFM OAMPDU messages for 802.1ag and Y.1731 use a standard Ethernet frame (see
Figure
Destination and Source Addresses
The destination and source MAC addresses of the CFM message must match at the send and
the receive routers. For example, a 7705 SAR-initiated ETH-CFM message would use the
spoke SDP MAC address of the 7705 SAR as the source MAC address and the spoke SDP
MAC address of the far-end router as the destination MAC address. At the far end, the
source and destination MAC addresses would be the reverse of the near end.
An exception to the matching source-destination MAC address requirement occurs for
linktrace and continuity messages, where the destination MAC address is set to a multicast
group address. The designated multicast group address for linktrace and CCM is 01-80-C2-
00-00-3x; where x represents the maintenance domain (MD) level (for 802.1ag) or the MEG
level (for Y.1731). For example, a dot1ag CCM message destined for 01-80-C2-00-00-31
corresponds to MD level 1.
CCM packets using source-destination multicast MAC addresses are for user-initiated
messages only (that is, loopbacks).
Ethertype (T)
If dot1q encapsulation is not configured, then the Ethertype value is 0x8902 and there is no
VLAN tag. If dot1q encapsulation is configured, the VLAN tag (Ethertype value 0x8100) is
present and is followed by the Ethertype value of 0x8902, which indicates ETH-CFM
messages. The Ethertype is not hard-coded to 0x8100 and can be changed via the port
configuration command.
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10). The parts of the frame are described below.

Figure 10: ETH-CFM Frame Format

Destination MAC
Source MAC
T = 8100
Vlan / Dot1p
T = 8902
ETH-CFM OAMPDU
FCS
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