Route attributes overwritten during reconfiguration

[Ondrej Zajicek]

On Mon, Nov 07, 2016 at 09:18:46PM -0800, João Taveira Araújo wrote:
> Hi,
> 
> I've run into a bug which manifests itself during reconfiguration.
> Unfortunately, the bird config in question is extremely large and I
> can't easily cut it down to something replicable. I'm running into
> this particular issue in bird6, but have no reason to believe IPv4
> would fair any better. All results are using bird 1.6.2.
...
> in this brief moment, a window of opportunity arises for our thus far
> silent transit to make an unwanted appearance:
> 
>       sudo birdc6 show route for 2001:db8::/48
>       BIRD 1.6.2 ready.
>       2001:db8::/48 dev lo [static_protocol 05:44:07] * (200)
>                    via xxx on et3 [transit_3 05:44:07] (100)
>                    via xxx on et1 [transit_1 03:44:07] (100)
>                    via xxx on et2 [transit_2 03:44:07] (100)

I don't understand this. Even if the route from transit_3 appears during
the window of opportunity, it should disappear as the static route is
propagated again to transit_3 and transit_3 selected it (assuming that
it is the reason why it was not propagated before).

> This, it turns out, is tragic, because somehow the extended
> communities we apply to the route learnt from transit_3 clobber the
> ones we apply in static_protocol.

How does this ext community clobbering is expressed? Could you document
it by appropriate 'show route all'?

> I'm pretty sure something screws up the rta associated to the static
> route, but I'm also confused as to why the static protocol seems to
> get reloaded at all given there is no configuration change in the
> first place.

That is true, it should not.

-- 
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."
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