Configuring Ldp Gr - HP 10500 SERIES Configuration Manual

Step
4. Configure the device to use IP
routes or LSPs to send back the
ICMP TTL exceeded messages
for TTL-expired MPLS packets
that have only one level of
label.

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 can be a GR restarter or a GR helper.
• GR restarter—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.
Figure 23 LDP GR
GR helper
Two LDP peers perform GR negotiation when establishing an LDP session. The LDP session established is
GR capable only when both peers support LDP GR.
LDP GR operates in the following procedure:
GR helper
GR restarter
GR helper
LDP session with GR capability
Command
•
(Approach 1) Use IP routes:
ttl expiration pop
•
(Approach 1) Use LSPs:
undo ttl expiration pop
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Remarks
Optional.
Use either approach as required.
By default, an ICMP TTL exceeded
message is sent back along an IP
route when the TTL of an MPLS
packet with a one-level label stack
expires.
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.