H3C Technologies H3C S10500 Series Switches - Manual (Page 83)

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a BFD control packet, forward the BFD control packet along the LSP to the egress, and determine 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 the connectivity 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. Such a BFD
session is used for connectivity detection of an LSP from the local device to the remote device.
Configuration prerequistes
• The BFD session parameters configured on the loopback interface whose IP address is configured
as the MPLS LSR ID are used, and the BFD packets use the MPLS LSR ID as the source address.
Therefore, before enabling BFD for an LSP, you must configure an IP address for the loopback
interface and configure the IP address as the MPLS LSR ID. You can also configure BFD session
parameters for the loopback interface as needed. For more information about BFD, see High
Availability Configuration Guide.
• To establish a static BFD session, ensure there is already an LSP from the local device to the remote
device and an LSP from the remote device to the local device.
Configuration procedure
Follow these steps to configure BFD for LSPs:
To do… Use the command… Remarks
Enter system view system-view —
Enable LSP verification and enter
the MPLS LSPV view
mpls lspv
Required
Not enabled by default
Configure BFD to detect LSP
connectivity
bfd enable destination-address
mask-length [ nexthop
nexthop-address [ discriminator
local local-id remote remote-id ] ]
Required
Not configured by default
NOTE:
•
You cannot establish both a static BFD session and a dynamic BFD session for the same LSP.
• After a static BFD session is established, it is not allowed to modify the discriminator values of the BFD
session.
• In a BFD session for detecting LSP connectivity, the ingress node always works in active mode and the
egress node always works in passive mode. The bfd session init-mode command does not take effect on
the ingress and egress nodes of such a BFD session. Even if you configure the two nodes to both work in
passive mode, the BFD session will still be established successfully.
• BFD for MPLS LDP is for detecting the IP connectivity between two remote LDP peers. BFD for LSP is for
detecting the connectivity of LSPs.