(Optional) Adjusting Session Detection Parameters

When you create a BFD session, adjust the BFD control packet sending interval, receiving interval, and local detection multiple of the device according to the network status and performance. The parameter adjustment does not affect the status of existing BFD sessions.

Context

The detection parameters of a BFD session include the BFD control packet sending interval, receiving interval, and local detection multiple. After detection parameters are changed, the mapping between valid parameters and configured parameters on the local and peer devices is as follows:

Actual BFD control packet sending interval in the local = maximum (configured local sending interval and configured peer receiving interval)
Actual BFD control packet receiving interval in the local = maximum (configured peer sending interval and configured local receiving interval)
In asynchronous mode, actual BFD control packet detection interval in the local = Actual local receiving interval x Configured peer BFD detection multiple
In demand mode, actual BFD control packet detection interval in the local = Actual local sending interval x Configured local BFD detection multiple

When the network is in poor quality or overloaded, increase the BFD detection interval as required.

A larger BFD detection interval is required when a low-speed interface (such as virtual template, dialer, or tunnel interface), the IPSec or L2TP tunnel is used.

If the FW is deployed between two routers, and the routers detect each other through BFD, you are advised to properly prolong the BFD time (longer than 100 ms is recommended) to prevent BFD flapping resulting from occasional network congestion.

For example:

The configured local sending interval is 300 ms, receiving interval is 300 ms, and detection multiple is 4.
The configured peer sending interval is 400 ms, receiving interval is 600 ms, and detection multiple is 5.

Then,

The actual sending interval in the local is the maximum value between 300 ms and 600 ms, namely, 600 ms. The actual receiving interval is the maximum value between 400 ms and 300 ms, namely, 400 ms. The actual detection interval in asynchronous mode is 2000 ms (400 ms x 5). The actual detection interval in demand mode is 2400 ms (600 ms x 4).
The actual sending interval on the peer end is the maximum value between 400 ms and 300 ms, namely, 400 ms. The actual receiving interval is the maximum value between 300 ms and 600 ms, namely, 600 ms. The actual detection interval in asynchronous mode is 2400 ms (600 ms x 4). The actual detection interval in demand mode is 2000 ms (400 ms x 5).

The system automatically changes the local sending interval and receiving interval to random values ranging from 2,000 ms to 3,000 ms upon detecting the BFD session in Down state. When the BFD session becomes Up, the system restores the intervals to the configured values. This limits the consumption over system resources.

Procedure

Access the system view.
```
system-view
```
Access the BFD session view.
```
bfd cfg-name
```
Set the BFD control packet sending interval.
```
min-tx-interval interval
```
By default, the minimum sending interval is 1000 ms.
Set the BFD control packet receiving interval.
```
min-rx-interval interval
```
By default, the minimum receiving interval is 1000 ms.
Set the local detection multiple.
```
detect-multiplier multiplier
```
By default, the local detection multiple is 3.
Commit the configuration.
```
commit
```
To change session parameters (by using the min-tx-interval, min-rx-interval, detect-multiplier, tos-exp, wtr, or description command) after a BFD session is created, you must run the commit command. In this case, the configurations can take effect.