Unwanted IPv6 static route flap

[Ondrej Zajicek]

On Mon, Mar 02, 2020 at 05:35:01PM +0000, Neil Jerram wrote:
> On Sat, Feb 29, 2020 at 1:05 PM Neil Jerram <neil at tigera.io> wrote:
> 
> > I am struggling to understand and ideally eliminate an unwanted flap (i.e.
> > delete and re-add) of an IPv6 route on node M, when a neighbouring node R
> > restarts, and R is configured to advertise that IPv6 route statically. [...]
> >
> 
> FYI I have just tried the same test again with DBG(...) statements compiled
> in, in the hope that that might reveal strange timing in the static
> protocol processing.  Unfortunately I don't think it revealed anything
> suspicious.  There is a line with

Hi

I would guess that the issue is more in node M than in node R. The fact
that it happens only for IPv6 can be explained by implementation of
Kernel protocol, which uses replace operation for IPv4 (since 2.0.5), but
only remove/add for IPv6. Technically, the kernel protocol should detect
that the new route is the same as old one and avoid pushing it to the
kernel, but perhaps for some reason it pushes it anyway and causes the
flap.

To debug this isse, it would be useful to enable 'debug { events, routes
}' on BGP and Kernel on node M. One could see if there are any withdraws,
or just updates.


-- 
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."