Subject: Demand Mode

From: "Shahram Davari" <[email-masked]>
Date: Thu, 27 Aug 2009 12:39:31 -0700

Hi,

What happens if a system is in Demand Mode and UP state and then due to some reason it exists the UP state? Does it automatically cause the local system to also exit the Demand mode? if so should this be signaled in the "D" bit?

Also When in Demand mode, if a system wants to check connectivity, should it issue periodic Poll packets at the Max {bfd.RemoteMinRxInterval, bfd.DesiredMinTxInterval} or it can send Poll packets at any rate or it must send one BFD packets and wait for the reception of the Final packet (or expiry of Detection Time) before sending the next BFD packet?

Thanks,
Shahram

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From: Dave Katz <[email-masked]>
Date: Thu, 27 Aug 2009 17:01:12 -0600

On Aug 27, 2009, at 1:39 PM, Shahram Davari wrote:

> Hi,
>
> What happens if a system is in Demand Mode and UP state and then due  
> to some reason it exists the UP state? Does it automatically cause  
> the local system to also exit the Demand mode? if so should this be  
> signaled in the "D" bit?

Please read the spec:

    Note that
    the Demand bit MUST NOT be set unless both systems perceive the
    session to be Up (the local system thinks the session is Up, and the
    remote system last reported Up state in the State (Sta) field of the
    BFD Control packet.)

>
> Also When in Demand mode, if a system wants to check connectivity,  
> should it issue periodic Poll packets at the Max  
> {bfd.RemoteMinRxInterval, bfd.DesiredMinTxInterval} or it can send  
> Poll packets at any rate or it must send one BFD packets and wait  
> for the reception of the Final packet (or expiry of Detection Time)  
> before sending the next BFD packet?

Please read the spec:

    A Poll Sequence consists of a system sending periodic BFD Control
    packets with the Poll (P) bit set.