OSPF/BFD reaction time under 1 second

[Ondrej Zajicek]

On Tue, Nov 12, 2019 at 09:06:31AM +0100, Patrik Rehuš wrote:
> Hello,
> 
> In my topology I have 2 parallel connections from one host to the same
> destination. The goal is to switch route to another one under 1 second (in
> case of broken link). For this I used OSPF with BFD. BFD use 40ms interval
> and multiplier is 5, so theoretical switching time to another link should
> be 200ms. In the measurements I find out that sometimes it is OK but
> sometimes it takes approximately 1 second longer (based on Wireshark it
> takes approx. 1,2s to switch). I think that it is due to tick parameter in
> OSPF settings, because base on the documentation „The routing table
> calculation and clean-up of areas' databases is not performed when a single
> link state change arrives. To lower the CPU utilization, it's processed
> later at periodical intervals of num seconds. The default value is 1“.
> 
> So, in my case I think that this feature destroys ability of BFD to switch
> link under 1 second. Is it correct? If yes, is it possible to set lower
> value than 1 second or completely disable this feature?

Hello

No, that is limitation of current implementation. I plan to implement
some smarter SPF delay algorithm (e.g. RFC 8405) in the future.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."