Contents

Configuring BFD· 1

Overview·· 1

BFD session establishment and termination· 1

BFD session modes and operating modes· 1

Supported features· 2

Protocols and standards· 2

Configuring BFD basic functions· 3

Configuring echo packet mode· 3

Configuring control packet mode· 3

Displaying and maintaining BFD·· 5

Configuring BFD

The term "interface" in this chapter collectively refers to Layer 3 interfaces, including VLAN interfaces and Layer 3 Ethernet interfaces. You can set an Ethernet port as a Layer 3 interface by using the port link-mode route command (see Layer 2—LAN Switching Configuration Guide).

BFD takes effect only in the default MDC.

Overview

Bidirectional forwarding detection (BFD) provides a general-purpose, standard, medium- and protocol-independent fast failure detection mechanism. It can detect and monitor the connectivity of links in IP to detect communication failures quickly so that measures can be taken to ensure service continuity and enhance network availability.

BFD can uniformly and quickly detect the failures of the bidirectional forwarding paths between two devices for upper-layer protocols such as routing protocols. The hello mechanism used by upper layer protocols needs seconds to detect a link failure, while BFD can provide detection measured in milliseconds.

BFD can be used for single-hop and multi-hop detections:

·          Single-hop detection—Detects the IP connectivity between two directly connected systems.

·          Multi-hop detection—Detects any of the paths between two systems. These paths have multiple hops, and might overlap.

BFD session establishment and termination

BFD does not provide any neighbor discovery mechanisms. The upper protocols notify BFD of the routers to which it needs to establish sessions.

Establishing BFD sessions

BFD sessions are established as follows:

1.        A protocol sends Hello messages to discover neighbors and establish neighborships.

2.        After establishing neighborships, the protocol notifies BFD of the neighbor information, including destination and source addresses.

3.        BFD uses the information to establish BFD sessions.

Terminating a BFD session

When BFD detects a link failure:

1.        BFD clears the neighbor session.

2.        BFD notifies the protocol of the failure.

3.        The protocol terminates the neighborship on the link.

4.        If a backup link is available, the protocol will use it for communication.

BFD session modes and operating modes

BFD sessions use the following types of packets:

·          Echo packets—Encapsulated into UDP packets with port number 3785.

·          Control packets—Encapsulated into UDP packets with port number 3784 for single-hop detection or port number 4784 for multi-hop detection.

Echo packet mode

The local end of the link sends echo packets to establish BFD sessions and monitor link status. The peer end does not establish BFD sessions and only forwards the packets back to the originating end.

In echo packet mode, BFD supports only single-hop detection and the BFD session is independent of the operating mode.

Control packet mode

Both ends of the link exchange BFD control packets to monitor link status.

Before a BFD session is established, BFD has two operating modes—active and passive.

·          Active mode—BFD actively sends BFD control packets regardless of whether any BFD control packet is received from the peer.

·          Passive mode—BFD does not send control packets until a BFD control packet is received from the peer.

At least one end must operate in active mode for a BFD session to be established.

After a BFD session is established, both ends must operate in one of the following BFD operating modes:

·          Asynchronous mode—Both endpoints periodically send BFD control packets to each other. BFD considers that the session is down if it receives no BFD control packets within a specific interval.

·          Demand mode—No BFD control packets are exchanged after the session is established. When the connectivity to another system needs to be verified explicitly, a system sends several BFD control packets that have the Poll (P) bit set at the negotiated transmit interval. If no response is received within the detection interval, the session is considered down. If the connectivity is found to be up, no more BFD control packets are sent until the next command is issued.

In addition, both ends of the link can exchange BFD control packets to establish and maintain BFD sessions, and one end of the link sends echo packets to monitor link status.

Supported features

·          Static routing. For more information, see Layer 3—IP Routing Configuration Guide.

·          IPv6 static routing. For more information, see Layer 3—IP Routing Configuration Guide.

·          RIP. For more information, see Layer 3—IP Routing Configuration Guide.

·          OSPF. For more information, see Layer 3—IP Routing Configuration Guide.

·          OSPFv3. For more information, see Layer 3—IP Routing Configuration Guide.

·          IS-IS. For more information, see Layer 3—IP Routing Configuration Guide.

·          IPv6 IS-IS. For more information, see Layer 3—IP Routing Configuration Guide.

·          BGP. For more information, see Layer 3—IP Routing Configuration Guide.

·          IPv6 BGP. For more information, see Layer 3—IP Routing Configuration Guide.

·          PIM. For more information, see IP Multicast Configuration Guide.

·          Track. For more information, see "Configuring Track."

·          IP fast reroute (FRR). IP FRR is supported by OSPF, RIP, IS-IS and static routing. For more information, see Layer 3—IP Routing Configuration Guide.

Protocols and standards

·          RFC 5880, Bidirectional Forwarding Detection (BFD)

·          RFC 5881, Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)

·          RFC 5882, Generic Application of Bidirectional Forwarding Detection (BFD)

·          RFC 5883, Bidirectional Forwarding Detection (BFD) for Multihop Paths

·          RFC 5885, Bidirectional Forwarding Detection (BFD) for the Pseudowire Virtual Circuit Connectivity Verification (VCCV)

Configuring BFD basic functions

Before configuring BFD basic functions, configure the network layer addresses of the interfaces so that adjacent nodes are reachable to each other at the network layer.

After a BFD session is established, the two ends negotiate BFD parameters, including minimum sending interval, minimum receiving interval, initialization mode, and packet authentication, by exchanging negotiation packets. They use the negotiated parameters without affecting the session status.

Configuring echo packet mode

Step	Command	Remarks
1.       Enter system view.	system-view	N/A
2.       Configure the source IP address of echo packets.	·         Configure the source IP address of echo packets: bfd echo-source-ip ip-address ·         Configure the source IPv6 address of echo packets: bfd echo-source-ipv6 ipv6-address	By default, no source IP address is configured for echo packets. As a best practice, do not configure the source IP address to be on the same network segment as any local interface's IP address. If you configure such a source IP address, a large number of ICMP redirect packets might be sent from the peer, resulting in link congestion. To prevent BFD echo packets from being dropped, disable ICMP redirect packet sending on the peer end. The source IPv6 address of echo packets can only be a global unicast address.
3.       Enter interface view.	interface interface-type interface-number	N/A
4.       (Optional.) Set the minimum interval for receiving BFD echo packets.	bfd min-echo-receive-interval value	The default setting is 400 milliseconds.
5.       (Optional.) Set the single-hop detection time multiplier.	bfd detect-multiplier value	The default setting is 5.

 

Configuring control packet mode

To configure control packet mode for single-hop detection:

 

Step	Command	Remarks
1.       Enter system view.	system-view	N/A
2.       Specify the mode for establishing a BFD session.	bfd session init-mode { active | passive }	By default, active is specified.
3.       Enter interface view.	interface interface-type interface-number	N/A
4.       Configure the authentication mode for single-hop control packets.	bfd authentication-mode { m-md5 | m-sha1 | md5 | sha1 | simple } key-id { cipher cipher-string | plain plain-string }	By default, single-hop BFD packets are not authenticated.
5.       Enable the Demand BFD session mode.	bfd demand enable	By default, the BFD session is in Asynchronous mode.
6.       Enable the echo packet mode.	bfd echo enable	By default, the echo packet mode is disabled. If you enable the echo packet mode for a BFD session in which control packets are sent and the session goes up, BFD periodically sends echo packets to detect link connectivity and decrease control packet receive rate.
7.       Set the minimum interval for transmitting single-hop BFD control packets.	bfd min-transmit-interval value	The default setting is 400 milliseconds.
8.       Set the minimum interval for receiving single-hop BFD control packets.	bfd min-receive-interval value	The default setting is 400 milliseconds.
9.       Set the single-hop detection time multiplier.	bfd detect-multiplier value	The default setting is 5.

 

To configure control packet mode for multi-hop detection:

 

Step	Command	Remarks
1.       Enter system view.	system-view	N/A
2.       Specify the mode for establishing a BFD session.	bfd session init-mode { active | passive }	By default, active is specified.
3.       Configure the authentication mode for multi-hop BFD control packets.	bfd multi-hop authentication-mode { m-md5 | m-sha1 | md5 | sha1 | simple } key-id { cipher cipher-string | plain plain-string }	By default, no authentication is performed.
4.       Configure the destination port number for multi-hop BFD control packets.	bfd multi-hop destination-port port-number	The default setting is 4784.
5.       Set the multi-hop detection time multiplier.	bfd multi-hop detect-multiplier value	The default setting is 5.
6.       Set the minimum interval for receiving multi-hop BFD control packets.	bfd multi-hop min-receive-interval value	The default setting is 400 milliseconds.
7.       Set the minimum interval for transmitting multi-hop BFD control packets.	bfd multi-hop min-transmit-interval value	The default setting is 400 milliseconds.

 

Displaying and maintaining BFD

Execute the display command in any view and the reset command in user view.

 

Task	Command
Display BFD session information.	display bfd session [ discriminator value | verbose ]
Clear BFD session statistics.	reset bfd session statistics