BFD for LDP LSP
Bidirectional Forwarding Detection (BFD) improves network reliability by quickly detecting LDP LSP faults and triggering traffic switchover upon LDP LSP faults.
Background
If a node or link along a working LDP LSP fails, traffic is switched to the backup LSP. The fault detection mechanism of LDP is slow so traffic switching between primary and backup LDP LSPs takes a relatively long time, causing traffic loss.
Figure 1 shows fault detection through the exchange of Hello messages.
In Figure 1, an LSR periodically sends Hello messages to its neighboring LSRs to advertise its network existence and maintain adjacencies. An LSR creates a Hello timer for each neighbor to maintain an adjacency. Each time the LSR receives a Hello message, the LSR resets the Hello timer. If the Hello timer expires before the LSR receives a new Hello message, the LSR considers the adjacency terminated. Exchange of Hello messages cannot detect link faults quickly, especially when a Layer 2 device is deployed between LSRs.
BFD for LDP LSP quickly detects faults on an LDP LSP and triggers a traffic switchover upon LDP LSP failures, minimizing packet losses and improving network reliability.
Implementation
BFD for LDP LSP rapidly detects faults on LDP LSPs and notifies the forwarding plane of the fault to ensure fast traffic switchover.
The implementation process is as follows:
A BFD session is bound to an LSP established between ingress and egress nodes.
A BFD packet is sent from the ingress node to the egress node along an LSP.
The egress node responds to the BFD packet, allowing the ingress node to quickly detect the LSP status.
After BFD detects an LSP failure, it notifies the forwarding plane.
The forwarding plane switches traffic to the backup LSP.
The following figure shows quick fault detection using BFD for LDP LSP.
