bgp keepalive & hold timers

[Ondrej Zajicek]

On Mon, Apr 18, 2022 at 04:43:32AM +0200, Alexander Zubkov wrote:
> For example bird can check that the hold timer proposed by a peer is
> at least 2 times greater than the local keepalive timer as in the
> attached patch.

Hi

Thanks for the patch. You are right, it would be a good idea to check
the hold time against the configured keepalive time. It is a question
where to put the cutoff, as technically even longer keepalive intervals
(than half of hold times) are viable, so in corner cases it may break
some working setups. I think that rejecting session when hold timer is
smaller than local keepalive (so it is clear misconfiguration), and just
a warning when it is smaller than 2*keepalive would be a good approach.
Will look at that.


> On Mon, Apr 11, 2022 at 1:12 PM Alexander Zubkov <green at qrator.net> wrote:
> >
> > Hi,
> >
> > Found interesting thing. If I set "keepalive time" for a BGP session,
> > this values is not modified after the hold time negotiations and as a
> > result I can get a BGP session with hold timer less than keepalive
> > timer and it will die due to hold timer expired after some time.
> > https://gitlab.nic.cz/labs/bird/-/blob/692055e3df6cc9f0d428d3b0dd8cdd8e825eb6f4/proto/bgp/packets.c#L908
> > I think more correct bahivour would be to close the BGP session with
> > unacceptable hold timer error in such case.



-- 
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."