Operation Manual – MPLS Basics
H3C S9500 Series Routing Switches
Chapter 1 MPLS Basics Configuration
1-17
1.3.4 LDP Loop Detection
LSPs established in MPLS may be looping. The LDP loop detection mechanism can
detect looping LSPs and prevent LDP messages from looping forever.
The LDP loop detection mechanism must be configured on all LSR for it to work.
However, for an LDP session to be established, LDP loop detection configuration on
LDP peers may be different.
LDP loop detection can be in either of the following two modes:
I. Maximum hop count
A label request message or label mapping message can include 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 the attempt to establish an LSP fails.
II. Path vector
A label request message or label mapping message can include path information in the
format of path vector list. When such a message reaches an LSR, the LSR checks the
path vector list of the message to see whether its MPLS LSR ID is in the list. If either of
the following cases occurs, the attempt to establish an LSP fails:
z
The MPLS LSR ID of the LSR is already in the path vector list.
z
Hop counts of the path reaches the specified limit.
If the MPLS LSR ID of the LSR is not in the path vector list, the LSR adds it into the list.
1.4 Configuring MPLS Basic Capability
1.4.1 Configuration Prerequisites
Before configuring MPLS basic capability, be sure to complete these tasks:
z
Configuring physical parameters on related interfaces
z
Configuring link layer attributes on related interfaces
z
Configuring IP addresses for related interfaces
z
Configuring static routes or an IGP protocol, ensuring that LSRs can reach each
other
Note:
MPLS basic capability can be configured on LSRs even when LSRs cannot reach each
other. However, you must configure the
mpls ldp transport-address
command in this
case.
