33
Figure 17 Label acceptance control diagram
A label advertisement policy on an LSR and a label acceptance policy on its upstream LSR can
achieve the same purpose. As a best practice, use the label advertisement policy to reduce network
load.
You must create an IP prefix list before you configure a label acceptance policy. For information
about IP prefix list configuration, see
Layer 3—IP Routing Configuration Guide
.
To configure a label acceptance policy:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter LDP view or enter
LDP-VPN instance
view.
•
Enter LDP view:
mpls ldp
•
Enter LDP-VPN instance view:
a. mpls ldp
b. vpn-instance
vpn-instance-name
N/A
3.
Configure an IPv4 label
acceptance policy.
accept-label peer
peer-lsr-id
prefix-list
prefix-list-name
By default, LDP accepts all IPv4
FEC-label mappings.
4.
Configure an IPv6 label
acceptance policy.
ipv6 accept-label peer
peer-lsr-id
prefix-list
prefix-list-name
By default, LDP accepts all IPv6
FEC-label mappings.
Configuring LDP loop detection
The LDP loop detection feature enables LDP to detect loops during an LSP establishment. If LDP
detects a loop, it terminates the LSP establishment. This feature is applicable to an MPLS network
where most of the devices do not support the TTL mechanism.
LDP detects and terminates LSP loops in the following ways:
•
Maximum hop count loop detection
—LDP adds a hop count in a label request or label
mapping message. The hop count value increments by 1 on each LSR. When the maximum
hop count is reached, LDP determines that a loop has occurred and terminates the LSP
establishment.
•
Path vector loop detection
—LDP adds LSR ID information in a label request or label mapping
message. Each LSR checks whether its LSR ID is contained in the message. If it is not, the LSR
adds its own LSR ID into the message. If it is, the LSR determines that a loop has occurred and
terminates the LSP establishment. In addition, when the number of LSR IDs in the message
Do
n
ot
filt
er
la
be
l
m
ap
pin
gs
