H3C Technologies H3C S10500 Series Switches - Manual (Page 79)

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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.
NOTE:
For more information about HoVPN and nested VPN, see the chapter “MPLS L3VPN configuration.”
Follow these steps to configure the device to send back an ICMP TTL exceeded message for a received
MPLS TTL expired packet:
To do… Use the command… Remarks
Enter system view system-view —
Enter MPLS view mpls —
Enable the device to send back an
ICMP TTL exceeded message when
it receives an MPLS TTL expired
packet
ttl expiration enable
Optional
Enabled by default.
Specify that ICMP TTL exceeded
messages for MPLS packets with
only one-level of label travel along
the IP routes
ttl expiration pop
Specify that ICMP TTL exceeded
messages for MPLS packets with
only one-level of label travel along
the LSPs
undo ttl expiration pop
Optional
Configure one of them as required.
By default, ICMP TTL exceeded
messages for MPLS packets with
only one-level of label travel along
the local IP routes.
This configuration does not take
effect when the MPLS packets carry
multiple levels of labels. ICMP TTL
exceeded messages for such MPLS
packets always travel along the
LSPs.
Configuring LDP GR
MPLS has two separate planes: the forwarding plane and the control plane. Using this feature, LDP
Graceful Restart (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.
A device that participates in a GR process plays either of the following two roles:
• GR restarter, the router that gracefully restarts due to a manually configured command or a fault. It
must be GR-capable.
• GR helper, neighbor of the GR restarter. A GR helper maintains the neighbor relationship with the
GR restarter and helps the GR restarter restore its LFIB information. A GR helper must be
GR-capable.