Bfd Dampening; Bfd Hardware Offload - Cisco ASR 9000 Series Configuration Manual

Implementing BFD
• A BFD session on the member interfaces can belong to only one mode (Cisco or IETF mode). Mix of

BFD Dampening

Bidirectional Forwarding Detection (BFD) is a mechanism used by routing protocols to quickly realize and
communicate the reachability failures to their neighbors. When BFD detects a reachability status change of
a client, its neighbors are notified immediately. Sometimes it might be critical to minimize changes in routing
tables so as not to impact convergence, in case of a micro failure. An unstable link that flaps excessively can
cause other devices in the network to consume substantial processing resources, and that can cause routing
protocols to lose synchronization with the state of the flapping link.
The BFD Dampening feature introduces a configurable exponential delay mechanism. This mechanism is
designed to suppress the excessive effect of remote node reachability events flapping with BFD. The BFD
Dampening feature allows the network operator to automatically dampen a given BFD session to prevent
excessive notification to BFD clients, thus preventing unnecessary instability in the network. Dampening the
notification to a BFD client suppresses BFD notification until the time the session under monitoring stops
flapping and becomes stable.
Configuring the BFD Dampening feature, especially on a high-speed interface with routing clients, improves
convergence time and stability throughout the network. BFD dampening can be applied to all types of BFD
sessions, including IPv4/single-hop/multihop, Multiprotocol Label Switching-Transport Profile (MPLS-TP),
and Pseudo Wire (PW) Virtual Circuit Connection Verification (VCCV).
BFD Session Dampening
You can configure the BFD Dampening feature at the BFD template level (both single-hop and multihop
templates). Dampening is applied to all the sessions that use the BFD template. If you choose not to have a
session to be dampened, you should use a new BFD template without dampening for a new session. By default,
the dampening functionality is not enabled on a template.

BFD Hardware Offload

The Bidirectional Forwarding Detection (BFD) hardware offload feature allows the offload of asynchronous
BFD transmission (Tx) and reception (Rx) to the network processing unit on the ASR 9000 Enhanced Ethernet
Line Card. BFD hardware offload improves scale and reduces the overall network convergence time by sending
rapid failure detection packets (messages) to the routing protocols for recalculating the routing table.
The below asynchronous BFD sessions are offloaded to the network processor unit on the ASR 9000 Enhanced
Ethernet Line Card:
• BFD IPv4 sessions over physical and VLAN interfaces.
• BFD IPv6 sessions over physical and VLAN interfaces.
• BFD over MPLS-TP LSP Single-Path (SP) sessions.
BFD hardware offload mode is enabled on the ASR 9000 Enhanced Ethernet Line Card using the hw-module
bfd-hw-offload enable command in admin mode.
OL-30423-03
the modes within the same bundle is not supported.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
BFD Dampening
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