15
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter MPLS LDP view.
mpls ldp
N/A
3.
Specify the label distribution
control mode.
label-distribution
{
independent
|
ordered
}
Optional.
The default mode is
ordered
.
For LDP sessions existing before
the command is configured, you
must reset the LDP sessions for
the specified label distribution
control mode to take effect.
4.
Enable label
re-advertisement for DU
mode.
du-readvertise
Optional.
By default, label re-advertisement
for DU mode is enabled.
5.
Set the interval for label
re-advertisement in DU
mode.
du-readvertise
timer
value
Optional.
The default interval is 30 seconds.
Configuring LDP loop detection
LSPs established in an MPLS domain might be looping. The LDP loop detection mechanism can
detect looping LSPs and prevent LDP messages from looping forever.
LDP loop detection can be in either of the following modes:
•
Maximum hop count
—A label request message or label mapping message carries
information about its hop count, which increments by 1 for each hop. When this value reaches
the specified limit, LDP considers that a loop is present and terminates the establishment of the
LSP.
•
Path
vector
—A label request message or label mapping message carries path information in
the form of path vector list. When such a message reaches an LSR, the LSR examines the path
vector list of the message for its MPLS LSR ID. If its MPLS LSR ID is not in the list, the LSR
adds its LSR ID to the path vector list. If it is in the list, the LSR considers that a loop has
occurred and terminates the establishment of the LSP.
The path vector mode also limits the number of hops of an LSP. An LSR also terminates the
establishment of an LSP when the hop count of the path, or the length of the path vector,
reaches the upper limit.
Configuration guidelines
•
The loop detection modes configured on two LDP peers must be the same for setting up an
LDP session.
•
To implement loop detection in an MPLS domain, you must enable loop detection on every LSR
in the MPLS domain.
•
Configure loop detection before enabling LDP capability on any interface.
•
All loop detection configurations take effect only on the LSPs established after the
configurations. Changing the loop detection settings does not affect existing LSPs. You can
execute the
reset mpls ldp
command in user view, so the loop detection settings also take
effect on existing LSPs.
•
LDP loop detection can result in LSP update, which generates redundant information and
consume many system resources. As a best practice, configure the routing protocol's loop
detection mechanism.
Configuration procedure
To configure LDP loop detection: