Cisco ASR 9000 Series Configuration Manual page 330
Aggregation services router mpls
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- Command reference manual (1138 pages) ,
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Fault OAM Support
• Generic Associated Channel
• Fault Management: Alarm Indication Signal (AIS), Link Down Indication (LDI), and Lock
Report (LKR) messages
• Fault Management: Emulated Protection Switching for LSP Lockout
• LSP ping and traceroute
Cisco ASR 9000 Series Aggregation Services Router MPLS Configuration Guide, Release 4.3.x
314
Generic Associated Channel (G-ACh) is the control channel mechanism associated with MPLS
LSPs in addition to MPLS pseudowire. The G-ACh Label (GAL) (Label 13) is a generic alert
label to identify the presence of the G-ACh in the label packet. It is taken from the reserved MPLS
label space.
G-ACh or GAL is used to support in-band OAMs of MPLS-TP LSPs and pseudowires. The OAM
messages are used for fault management, connection verification, continuity check and other
functions.
These messages are forwarded along the specified MPLS LSP:
• OAM Fault Management: Alarm Indication Signal (AIS), Link Down Indication (LDI), and
Lock Report (LKR) messages (GAL with fault-OAM channel)
• OAM Connection Verification: Ping and traceroute messages (GAL with IP channel)
• BFD messages (GAL with BFD channel)
These messages are forwarded along the specified pseudowire:
• Static pseudowire OAM messages (static pseudowire status)
• Pseudowire ping and traceroute messages
LDI messages are generated at midpoint nodes when a failure is detected. The midpoint sends
the LDI message to the endpoint that is reachable with the existing failure. The midpoint node
also sends LKR messages to the reachable endpoint, when an interface is administratively down.
AIS messages are not generated by Cisco platforms, but are processed if received. By default, the
reception of LDI and LKR on the active LSP at an endpoint will cause a path protection switchover,
while AIS will not.
You can implement a form of Emulated Protection Switching in support of LSP Lockout using
customized fault messages. When a Cisco Lockout message is sent, it does not cause the LSP to
be administratively down. The Cisco Lockout message causes a path protection switchover and
prevents data traffic from using the LSP. The LSP's data path remains up so that BFD and other
OAM messages can continue to traverse it. Maintenance of the LSP can take place such as
reconfiguring or replacing a midpoint LSR. BFD state over LSP must be up and MPLS ping and
traceroute can be used to verify the LSP connectivity, before the LSP is put back into service by
removing the lockout. You cannot lockout working and protect LSPs simultaneously.
For MPLS-TP connectivity verification, you can use ping mpls traffic-eng tunnel-tp and
traceroute mpls traffic-eng tunnel-tp commands. You can specify that the echo requests be sent
along the working LSP or the protect LSP. You can also specify that the echo request be sent on
a locked out MPLS-TP tunnel LSP (either working or protect) if the working or protect LSP is
explicitly specified.
Implementing MPLS Transport Profile
OL-28381-02
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