How does BIRD detect the connected network type for ospf neighbor

[Ondrej Zajicek]

On Mon, Dec 05, 2016 at 04:20:23PM +0000, Wei Huang wrote:
> When I set my ospf interface eth1's address to be 10.2.1.2/30, neighbor router ethernet interface IP address to be 10.2.1.1/30, the neighbor shows it's PTP type:
> 
> 
> bird> sh ospf neighbors
> ospf_rdomain_0:
> Router ID       Pri          State      DTime   Interface  Router IP
> 172.16.20.76      1     Full/PtP        00:35   vni-0      10.2.1.1
> 
> 
> If I change the interfaces' IP address to be 10.2.1.x/24 or I force interface type to be bcast in Bird's ospf config, it shows as
> 
> bird> sh ospf neighbors
> ospf_rdomain_0:
> Router ID       Pri          State      DTime   Interface  Router IP
> 172.16.20.76      1     Full/DR         00:35   vni-0      10.2.1.1
> 
> My question is how does Bird detect the connected network type?

Hi

Generally based on iface multicast ability and address range:

multicast, big range -> Type Broacast
multicast, small range -> Type PtP
no multicast, big range -> Type NBMA
no multicast, small range -> Type PtMP

Where small range is prefix length 30, 31 or 32.

Other combinations are possible, but PtP and Broadcast require multicast
ability; Broadcast and NBMA require regular prefix (prefix length < 32).

-- 
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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