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PS for an MPLS TE tunnel
Protection switching (PS) refers to establishing one or more protection tunnels (backup tunnels) for a main
tunnel. A main tunnel and its protection tunnels form a protection group. When the main tunnel fails, data
is switched to a protection tunnel immediately, greatly improving the reliability of the network. When the
main tunnel recovers, data can be switched back to the main tunnel.
Protection switching modes
The device supports 1:1 protection switching. Two tunnels, one main and one backup, exist between the
ingress node and the egress node. Normally, user data travels along the main tunnel. If the ingress node
detects a fault on the main tunnel by using a probing mechanism (such as BFD), it switches data to the
backup tunnel.
Protection switching triggering modes
Protection switching may be command triggered or signal triggered.
• Command switching refers to a PS triggered by an externally configured switching command,
which can define the following switching actions (in descending order of priority):
{ clear—Clears all configured switching actions.
{ lock (lockout of protection)—Always uses the main LSP to transfer data.
{ force (forced switch)—Forces data to travel on the backup LSP.
{ manual (manual switch)—Switches data from the main LSP to the backup LSP.
• Signal switching (Signal Fail) refers to a PS automatically triggered by a signal fail declaration. For
example, a PS that occurs during BFD detection for MPLS TE tunnels.
The following shows the externally configured switching actions and the signal fail switchings, in the
descending order of priority:
• Clear
• Lockout of protection
• Signal fail of the backup LSP
• Forced switch
• Signal fail of the main LSP
• Signal clear
• Manual switch
In practice, a manually configured switching action takes effect only when its priority is higher than that
of the current switching action. To change a switching action to a lower-priority switching action, first
execute the mpls te protect-switch clear command and then configure the low-priority switching action.
Path switching modes
The main and backup tunnels in a protection group support unidirectional path switching. Only the
ingress node performs path switching. The ingress node does not notify the egress node to perform path
switching.
Protocols and standards
• RFC 2702, Requirements for Traffic Engineering Over MPLS
• RFC 3212, Constraint-Based LSP Setup using LDP
• RFC 2205, Resource ReSerVation Protocol
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