Calculate the backpressure timer value of PFC frames

For S series switches that support BGP, the value of Hold and Keepalive timers can be set with the peer timer command. This command specifies the hold time when the BGP connection is interrupted and the interval for sending Keepalive messages. Large values of the two timers reduce the impact of link flapping, and small values enable the device to detect link changes. After the peer relationship is set up, the values of the two timers are negotiated by both peers, and the smaller ones are used.

You can run the peer timer command to set the durations of the Hold timer and Keepalive timer. This command specifies the timeout period of the BGP connection and the interval to send the Keepalive message. A longer timeout period can relieve the impact of link flapping, whereas a shorter timeout period makes the timer rapidly perceive link changes. After connections are established between two peers, the durations of the two timers are negotiated by the two peers and the shorter durations are adopted.

The functions and default values of IS-IS timers are as follows: CSNP Timer 10s csnp-interval: specifies the interval for sending CSNPs on a broadcast network. HELLO Timer 10s (3s for the DIS) Specifies the interval for sending Hello messages. lsp-retransmit Timer 5s Specifies the interval for re-sending LSP packets, that is, the interval between marking LSP packets with SRM on a P2P link and sending LSP packets. lsp-throttle Timer 50 ms Specifies the minimum interval for sending LSP packets. lsp-generation Timer 2s Specifies the maximum interval for generating LSP packets. lsp-max-age Timer 1200s Specifies the maximum Keepalive time of an LSP generated by the current IS-IS process, which is configured using the timer lsp-max-age command. lsp-refresh Timer 900s Specifies the LSP refresh interval, which is configured using the timer lsp-refresh command. spf 10s Specifies the maximum delay in route calculation. PSNP Timer 5s Specifies the interval between marking PSNPs with SSN and sending PSNPs. Specifies the minimum interval for sending packets on a broadcast network. 50 ms Specifies the interval between marking LSP packets with SRM and sending LSP packets.

Priority-based Flow Control (PFC) is a flow control mechanism based on priority. After the data center bridging (DCB) function is enabled on a switch and negotiation succeeds, the switch stops sending packets in the corresponding priority queue when it receives PFC frames. Number of required PFC frames = Interface bandwidth/[512 x Time(n)] Time(n) indicates the backpressure timer value. The unit is the time an interface uses to send 521 bits.

The procedure for setting the length of a Jumbo frame is described on the right.