Cisco Cisco Packet Data Gateway (PDG)
Routing
Bidirectional Forwarding Detection ▀
ASR 5000 System Administration Guide, StarOS Release 18 ▄
293
Bidirectional Forwarding Detection
Bidirectional Forwarding Detection (BFD) is a network protocol used to detect faults between two forwarding engines
connected by a link. BFD establishes a session between two endpoints over a particular link. If more than one link exists
between two systems, multiple BFD sessions may be established to monitor each one of them. The session is established
with a three-way handshake, and is torn down the same way. Authentication may be enabled on the session. A choice of
simple password, MD5 or SHA1 authentication is available.
connected by a link. BFD establishes a session between two endpoints over a particular link. If more than one link exists
between two systems, multiple BFD sessions may be established to monitor each one of them. The session is established
with a three-way handshake, and is torn down the same way. Authentication may be enabled on the session. A choice of
simple password, MD5 or SHA1 authentication is available.
Overview of BFD Support
BFD does not have a discovery mechanism; sessions must be explicitly configured between endpoints. BFD may be
used on many different underlying transport mechanisms and layers, and operates independently of all of these.
Therefore, it needs to be encapsulated by whatever transport it uses.
used on many different underlying transport mechanisms and layers, and operates independently of all of these.
Therefore, it needs to be encapsulated by whatever transport it uses.
Protocols that support some form of adjacency setup, such as OSPF or IS-IS, may also be used to bootstrap a BFD
session. These protocols may then use BFD to receive faster notification of failing links than would normally be
possible using the protocol's own keepalive mechanism.
session. These protocols may then use BFD to receive faster notification of failing links than would normally be
possible using the protocol's own keepalive mechanism.
In asynchronous mode, both endpoints periodically send Hello packets to each other. If a number of those packets are
not received, the session is considered down.
not received, the session is considered down.
When Echo is active, a stream of Echo packets is sent to the other endpoint which then forwards these back to the
sender. Echo can be globally enabled via the bfd-protocol command, and/or individually enabled/disabled per interface.
This function is used to test the forwarding path on the remote system.
sender. Echo can be globally enabled via the bfd-protocol command, and/or individually enabled/disabled per interface.
This function is used to test the forwarding path on the remote system.
The system supports BFD in asynchronous mode with optional Echo capability via static or BGP routing.
Important:
On an ASR 5000 one of the packet processing cards must be configured as a demux card in order for
BFD to function. See the Configuring a Demux Card section in the System Settings chapter for additional information.
Configuring BFD
This section describes how to configure and enable basic BFD routing protocol support in the system.
There are several factors affecting the configuration of BFD protocol: