H3C Technologies H3C S7500E Series Switches - Manual (Page 68)

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the first method is not applicable. In this case, you can configure the undo ttl expiration pop
command on these devices so that the devices use the second method.
For details about HoVPN and nested VPN, see MPLS L3VPN Configuration in the MPLS
Configuration Guide .
Follow these steps to configure sending of MPLS TTL timeout messages (ICMP error messages):
To do… Use the command… Remarks
Enter system view system-view —
Enter MPLS view mpls —
Enable the device to send an
ICMP error message when the
TTL of an MPLS packet expires
ttl expiration enable
Optional
Enabled by default.
Specify that TTL timeout
messages for MPLS packets with
only one-level of labels travel
along the IP routes
ttl expiration pop
Specify that TTL timeout
messages for MPLS packets with
only one-level of labels travel
along the LSPs
undo ttl expiration pop
Optional
Configure one of them as required.
By default, MPLS TTL timeout
messages for MPLS packets with
only one-level of labels travel
along the local IP routes.
This configuration does not take
effect when the MPLS packets
carry multiple levels of labels.
MPLS TTL timeout messages for
such MPLS packets always travel
along the LSPs.
Configuring LDP GR
LDP GR Overview
MPLS has two separate planes: the forwarding plane and the control plane. Using this feature, LDP
GR preserves the LFIB information when the signaling protocol or control plane fails, so that LSRs can
still forward packets according to LFIB, ensuring continuous data transmission.
z
GR Restarter, or graceful restarting router, is where protocol restart is triggered administratively
or because of a fault. It must be Graceful Restart capable.
z
GR Helper is the neighbor of the GR Restarter. It helps the GR Restarter maintain routing
information. It must be Graceful Restart capable.