FS S5900-24S4T2Q Instruction sheet

S5900-24S4T2Q SWITCH BFD CONFIGURATION
BFD Configuration
Model: S5900-24S4T2Q

S5900-24S4T2Q SWITCH BFD CONFIGURATION
Table of Contents
1. Configuring BFD......................................................................................................................................................................................1
1.1 Overview.............................................................................................................................................................................................. 1
1.2 BFD Configuration Tasks............................................................................................................................................................... 1
1.2.1 Activating Port BFD.....................................................................................................................................................................1
1.2.2 Activating the Port BFD Query Mode......................................................................................................................................... 1
1.2.3 Activating Port BFD Echo............................................................................................................................................................2
1.2.4 Enabling Port BFD Authentication............................................................................................................................................. 2
1.3 Displaying the BFD Statistics Information.................................................................................................................................... 2
1.4 BFD Configuration Example.......................................................................................................................................................... 2

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1. Configuring BFD
1.1 Overview
BFD (Bidirectional Forwarding Detection) is a set of all-net uniform detection mechanism used for rapid detection and monitoring of
link or IP routing forwarding connectivity. To improve the performance of existing networks, communication troubles can be
detected rapidly between neighboring protocols so that a standby communication channel can be quickly established.
BFD can establish sessions between two machines to monitor bidirectional forwarding paths between the two machines and serve
upper-level protocols. The served upper-level protocol notifies BFD of the one with which the session is established. After the session
is established through the three-handshake mechanism, no reception of BFD control packets from the peer within the detection
time or the number of dropped echo packets outnumbering the allowed threshold causes trouble. This case is then reported to the
upper-level protocol for corresponding processing.
1.2 BFD Configuration Tasks
1.2.1 Activating Port BFD
Port BFD is not activated by default.
After port BFD is enabled, BFD configured through dynamic protocols takes effect. Run the following command to achieve the
previous purpose:
Command
Purpose
bfd enable <cr> | [min_tx_interval <tx_value> min_rx_interval
<rx_value> multiplier <m_value>]
Activates port BFD.
Before the BFD session is established, the BFD control packets are transmitted in an interval of no less than 1 second so as to narrow
down traffic. After the session is established, the BFD control packets are transmitted in a negotiated interval so as to realize rapid
detection. During the establishment of BFD session, the transmission interval and detection time of BFD control packets are also
determined via packet exchange. In an effective BFD session, these timers can be modified through negotiation at any time without
affecting the session status. The timer negotiations at different BFD session directions are conducted independently and the
bidirectional timers can be different. The transmission interval for BFD control packets is the maximum value between local
min_tx_interval and peer min_rx_interval, that is to say, the comparatively slow part decides the transmission frequency.
The detection time is Detect Mult in peer BFD control packets multiplied the negotiated transmission interval of peer BFD control
packets. If you increase min_tx_interval of the local end, the actual transmission interval of BFD control packets on the local end
cannot be modified until the packets reset by the peer's F field are received, which ensures that the detection time is lengthened on
the peer before the increase of the transmission interval of BFD control packets on the local end. Otherwise, the detection timer on
the peer may time out.
If min_rx_interval on the local end is decreased, the local detection time cannot be modified until the packets reset by the peer’s F
field are received, which ensures that the transmission interval of BFD control packets on the peer has been decreased before the
decrease of local detection time. However, if min_tx_interval is decreased, the local transmission interval of BFD control packets may
decrease immediately; if min_rx_interval is increased, the local detection time will increase immediately.
1.2.2 Activating the Port BFD Query Mode
The port BFD query mode is not activated by default.
In query mode, we suppose that each system has an independent method to confirm its connection with other systems. Once a BFD
session is established, the system stops transmitting BFD control packets unless a certain system requires explicit connectivity
checkup. In a system where explicit connectivity checkup is required, the system transmits short-sequence BDF control packets and
claims the session is down if it doesn't receive the response packets in the checkup period. If the response packets are received from
the peer in the checkup period, it means the forwarding path is normal and the BFD control packets then stop being transmitted.
Run the following command to achieve the previous purpose:
Command
Purpose
bfd demand enable
Activates the BFD query mode.
The system supports to activate or deactivate the BFD query mode.

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1.2.3 Activating Port BFD Echo
Port BFD echo is not activated by default.
After the BFD echo is activated, if the neighbor supporting BFD echo is up, the control packets are transmitted according to the
interval configured by slow-timers. The connectivity detection is finished by the echo packets and the transmission interval of echo
packets is the time configured by min_echo_rx_interval.
Run the following command to achieve the previous purpose:
Command
Purpose
bfd echo enable <cr>|<number>
Activates BFD echo.
The activation and shutdown of echo functionality on an already “up” neighbor has no impact on this neighbor’s status, but the
transmission interval of control packets is affected.
1.2.4 Enabling Port BFD Authentication
Port BFD authentication is not activated by default.
Authentication configuration takes immediate effect before BFD neighbor is up, and the two terminals of a link on which BFD
detection is conducted can be up only when their BFD authentication configurations are same. But if authentication configuration is
modified after BFD neighbor is up, the same configurations or different configurations on the two terminals have no any impact on
the BFD neighbor’s status.
Run the following command to achieve the previous purpose:
Command
Purpose
bfd authentication-mode [md5 | meticulous md5 | simple]
<key id> <key>
Enables the BFD authentication function.
1.3 Displaying the BFD Statistics Information
You can run the following commands to display all kinds of BFD statistics information:
Command
Purpose
show bfd interfaces [details]
Displays the ports in the system on which BFD is activated.
show bfd neighbors [details]
Displays BFD neighbors in the system.
1.4 BFD Configuration Example
You need to set related protocols for BFD detection and activate the BFD function on the corresponding port before configuring BFD.
The following example shows how BFD provides BGP with bidirectional detection:
Establish the EBGP relationship between A and B, and check the link through BFD.
A：
interface vlan1
ip address 1.1.1.1 255.255.255.0
bfd enable
no ip directed-broadcast
!
router bgp 100
no synchronization
bgp log-neighbor-changes
neighbor 1.1.1.2 remote-as 200
neighbor 1.1.1.2 fall-over bfd
!
B：
interface vlan1

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ip address 1.1.1.2 255.255.255.0
bfd enable
no ip directed-broadcast
!
router bgp 200
no synchronization
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 fall-over bfd
!