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network maintenance difficult. To find LSP failures in time and locate the failed node, the device
provides the following mechanisms:
•
MPLS LSP ping
•
MPLS LSP tracert
Configuring MPLS LSP ping
MPLS LSP ping is for testing the connectivity of an LSP. At the ingress, it adds the label for the FEC
to be inspected into an MPLS echo request, which then is forwarded along the LSP to the egress.
The egress processes the request packet and returns an MPLS echo reply to the ingress. An MPLS
echo reply carrying a success notification indicates that the LSP is normal, and an MPLS echo reply
carrying an error code indicates that the LSP has failed.
To test the connectivity of an LSP, perform the following task in any view:
Task Command
Use MPLS LSP ping to test MPLS
LSP connectivity.
ping lsp
[
-a
source-ip
|
-c
count
|
-exp
exp-value
|
-h
ttl-value
|
-m
wait-time
|
-r
reply-mode
|
-s
packet-size
|
-t
time-out
|
-v
]
*
ipv4
dest-addr
mask-length
[
destination-ip-addr-header
]
Configuring MPLS LSP tracert
MPLS LSP tracert is for locating LSP errors. It consecutively sends the MPLS echo requests along
the LSP to be inspected, with the TTL increasing from 1 to a specific value. Then, each hop along the
LSP returns an MPLS echo reply to the ingress due to TTL timeout. So, the ingress can collect
information about each hop along the LSP, so as to locate the failed node. You can also use MPLS
LSP tracert to collect important information about each hop along the LSP, such as the label
allocated.
To locate errors of an LSP, perform the following task in any view:
Task Command
Perform MPLS LSP tracert to
locate errors along an MPLS LSP.
tracert lsp
[
-a
source-ip
|
-exp
exp-value
|
-h
ttl-value
|
-r
reply-mode
|
-t
time-out
]
*
ipv4
dest-addr mask-length
[
destination-ip-addr-header
]
Configuring BFD for LSPs
You can configure BFD to detect the connectivity of an LSP.After the configuration, a BFD session is
established between the ingress and egress of the LSP. The ingress adds the label for the FEC into
a BFD control packet, forwards the BFD control packet along the LSP to the egress, and determines
the status of the LSP according to the reply received. Upon detecting an LSP failure, BFD triggers a
traffic switchover.
A BFD session for LSP connectivity detection can be static or dynamic.
•
Static
—If you specify the local and remote discriminator values by using the
discriminator
keyword when configuring the
bfd enable
command, the BFD session is established with the
specified discriminator values. Such a BFD session is used to detect theconnectivity of a pair of
LSPs in opposite directions (one from local to remote, and the other from remote to local)
between two devices.
•
Dynamic
—If you do not specify the local and remote discriminator values when configuring the
bfd enable
command, the MPLS LSP ping is run automatically to negotiate the discriminator
values and then the BFD session is established based on the negotiated discriminator values.