H3C Technologies H3C S6800 Series Switches - Manual (Page 44)

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Configuring LDP loop detection
LDP detects and terminates 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 it is not, the LSR adds its own LSR ID into
the message. If it is, 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.
• Enter LDP view:
mpls ldp
• Enter LDP-VPN instance view:
a. mpls ldp
b. vpn-instance vpn-instance-name
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:
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.
Configuring LDP session protection
If two LDP peers have both a direct link and an indirect link in between, you can configure this feature to
protect their LDP session when the direct link fails.
LDP establishes both a Link Hello adjacency over the direct link and a Targeted Hello adjacency over the
indirect link with the peer. When the direct link fails, LDP deletes the Link Hello adjacency but still
maintains the Targeted Hello adjacency. In this way, the LDP session between the two peers is kept