BGP connect retry time

[Ondrej Zajicek]

On Sun, Mar 28, 2021 at 11:28:44PM +0200, dev at kou.li wrote:
> Hello,
> 
> I am running bird's BGP on a slower link with accounted data. I would
> like to lower connection attempt frequency when the peer is down. I
> found only two parameters mentioning connection delays: 'connect delay
> time' and 'connect retry time'. From documentation, I understood to
> change the 'connect retry time' to slow down failed connection attempts,
> but the bird seems to use 'connect delay time' repeatedly if the
> connection fails (test: bird 1.6.6, peer's firewall drops all BGP
> packets). So, what is the 'connect retry time' used for?

Hi

BIRD uses 'connect retry time' for repeated attempts where connection
cannot be established, i.e. rather a maximum timeout for an attempt than
limit between attempts. When connection attempt explicitly failed
(e.g. received ICMP message about port closed), the protocol is
restarted and therefore 'connect delay time' is used.

(There is also 'error wait time', but that only happens when session
falied after being established.)

It is kind of counterintuitive oversight and we should add support for
something like minimum connect retry time, it was not that important
as overhead from unsuccessful connection attempt is usually negligible
(compared to say session flapping).

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."