Configuring LDP loop detection
LDP detects and terminate LSP loops in the following ways:
Maximum hop count—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 considers that a loop has occurred and terminates the establishment of the LSP.
Path vector—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 not, the LSR adds its own LSR ID into the message. If yes, the LSR considers that a loop has occurred and terminates LSP establishment. In addition, when the number of LSR IDs in the message reaches the path vector limit, LDP also considers that a loop has occurred and terminates LSP establishment.
To configure LDP loop detection:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter LDP view or enter LDP-VPN instance view. |
| N/A |
3. Enable loop detection. | loop-detect | By default, loop detection is disabled. After loop detection is enabled, the device uses both the maximum hop count and the path vector methods to detect loops. |
4. Specify the maximum hop count. | maxhops hop-number | By default, the maximum hop count is 32. |
5. Specify the path vector limit. | pv-limit pv-number | By default, the path vector limit is 32. |
![[NOTE: ]](images/note.png) | NOTE: The LDP loop detection feature is applicable only in networks comprised of devices that do not support TTL mechanism, such as ATM switches. Do not use LDP loop detection on other networks because it only results in extra LDP overhead. | |