On Tue, 2019-03-26 at 09:00 +0100, Cybertinus wrote: > On 2019-03-26 08:49, Kenth Eriksson wrote: > > On Mon, 2019-03-25 at 21:09 +0100, Ondrej Zajicek wrote: > > > CAUTION: This email originated from outside of the organization. > > > Do > > > not click links or open attachments unless you recognize the > > > sender > > > and know the content is safe. > > > > > > > > > On Mon, Mar 25, 2019 at 03:06:29PM +0000, Kenth Eriksson wrote: > > > > It seems as bird autodetects a /30 OSPF interface as ptp. > > > > > > > > bird> show ospf interface > > > > ospfv2_1: > > > > Interface eth0 (10.210.138.32/30) > > > > Type: ptp > > > > Area: 0.0.0.0 (0) > > > > State: PtP > > > > Priority: 0 > > > > Cost: 10 > > > > Hello timer: 10 > > > > Wait timer: 40 > > > > Dead timer: 40 > > > > Retransmit timer: 5 > > > > bird> > > > > > > > > Is this really correct behaviour? The peering Cisco router > > > > thinks > > > > the > > > > /30 network is a broadcast interface... > > > > > > Well, OSPF RFC speaks about broadcast and ptp > > > networks/interfaces, > > > but it > > > is not really explicit about which networks are 'broadcast' and > > > which > > > are > > > 'ptp'. One could think about medium types (ethernet vs. serial > > > link), > > > physical topologies (star/bus vs. ptp link) or addressing > > > (unnumbered > > > or 'ptp' addresses vs /30 vs wider prefix). > > > > > > BIRD uses the third approach and autodetect unnumbered / ptp / > > > /30 as > > > ptp, while wider prefix as broadcast (or PtMP / NBMA if the > > > interface > > > does not support multicast). That is because in such cases it is > > > not > > > possible to have more than two nodes in the same L3 network, so > > > it is > > > not > > > necessary to use the more complicated and error prone broadcast > > > mode. > > > > > > There is RFC 5309 that discusses this issue, which implies that > > > was > > > perhaps meant more in the first sense (medium types). > > > > > > It is possible that other implementations use other heuristics, > > > which > > > causes compatibility issues in default setting. Perhaps we could > > > change > > > it (in some major release) if there is a clear consensus about > > > the > > > proper > > > behavior. > > > > > > > I can see the rationale of saying that a /30 network can run with > > OSPF > > interfaces in ptp mode since there are only 2 hosts on it. That > > said, I > > *believe* the Cisco routers defaults to broadcast mode for a /30 > > which > > would cause some interop issues with the default settings. I don't > > know > > the default values for other vendors. > > > > Is it possible to change the autodetect using a function in the > > bird > > configuration file? E.g. if the prefix length of the interface is > > 31 or > > 32 then use ptp mode else use broadcast mode. > > If you are willing to change the default config with a config > setting, > why not just configure the OSPF interface as ptp or broadcast, as > needed? :). Not trying to be a smart-ass here, but just wondering > what > would be the added value of such a config setting? >
I see a great value of having a working autodetect of the OSPF interface type. That gives me the possibility to change my interface address without the need to touch my bird OSPF configuration. > > > -- > > > Elen sila lumenn' omentielvo > > > > > > Ondrej 'Santiago' Zajicek (email: [email protected]) > > > OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, > > > wwwkeys.pgp.net) > > > "To err is human -- to blame it on a computer is even more so." > > Kind regards, > Cybertinus
