announce IPV4 loopback via an OSPF v3 backbone

[Pim van Pelt]

Hoi,

On 3/27/24 10:08, Benoit Chesneau wrote:
> I was reading  the ospv3 spec and this linkhttps://networklessons.com/ospf/ospfv3-for-ipv4-
>   and  was wondering if such features is supported in bird 2. Can we
> announce loopbacks via OSPFv3 and remove the need to use OSPFv2 and ptp
> subnets ?
>
> I see it as a good opportunity to reduce the usage of the IPv4 addresses
>   if we can just advertise loopbacks...
I tried this today on two machines directly connected as vpp0-2:e1 <-> 
vpp0-3:e0 (marked in *green*)

root at vpp0-2:~# ip -br a
lo               UNKNOWN        127.0.0.1/8 ::1/128
loop0            UNKNOWN        192.168.10.2/32 2001:678:d78:200::2/128 
fe80::dcad:ff:fe00:0/64
e0               UP             192.168.10.2/32 2001:678:d78:200::2/128 
fe80::5054:ff:fef0:1120/64
*e1               UP 192.168.10.2/32 2001:678:d78:200::2/128 
fe80::5054:ff:fef0:1121/64 *
e2               DOWN
e3               DOWN

root at vpp0-3:/etc/bird# ip -br a
lo               UNKNOWN        127.0.0.1/8 ::1/128
loop0            UNKNOWN        192.168.10.3/32 2001:678:d78:200::3/128 
fe80::dcad:ff:fe00:0/64
*e0               UP             192.168.10.3/32 2001:678:d78:200::3/128 
fe80::5054:ff:fef0:1130/64 *
e1               UP             192.168.10.3/32 2001:678:d78:200::3/128 
fe80::5054:ff:fef0:1131/64
e2               DOWN
e3               DOWN


They both took the following OSPF configuration with Bird 2.14 --

protocol ospf v3 ospf4 {
*ipv4* { export where (source = RTS_DEVICE || source = RTS_STATIC); 
import all; };
   area 0 {
     interface "loop0" { stub yes; };
     interface "e0" { type pointopoint; cost 5; bfd off; };
     interface "e1" { type pointopoint; cost 5; bfd off; };
     interface "e2" { type pointopoint; cost 5; bfd off; };
     interface "e3" { type pointopoint; cost 5; bfd off; };
   };
}

OSPFv3 adjacency did establish, but no routes were exchanged (also none 
with filter 'export all; import all;') --

root at vpp0-3:/etc/bird# birdc show os ne
BIRD 2.14 ready.
ospf4:
Router ID       Pri          State      DTime   Interface  Router IP
192.168.10.2      1     Full/PtP        30.036  e0 fe80::5054:ff:fef0:1121

root at vpp0-3:/etc/bird# birdc show route protocol ospf4
BIRD 2.14 ready.
Table master4:
192.168.10.3/32      unicast [ospf4 15:29:07.337] I (150/0) [192.168.10.3]
         dev loop0
         dev e0
         dev e1


It would be really useful to let OSPF v3 learn and distribute IPv4 
routes with link local nexthops, like so:
|
pim at vpp0-2:~$ sudo ip ro add 192.168.10.3/32 via inet6 
*fe80::5054:ff:fef0:1130* dev e1
pim at vpp0-3:/etc/bird$ sudo ip ro add 192.168.10.2/32 via inet6 
|*fe80::5054:ff:fef0:1121*|dev e0
pim at vpp0-3:/etc/bird$ ping ||192.168.10.2|
|PING 192.168.10.2 (192.168.10.2) 56(84) bytes of data.
64 bytes from 192.168.10.2: icmp_seq=1 ttl=64 time=3.90 ms
64 bytes from 192.168.10.2: icmp_seq=2 ttl=64 time=3.61 ms
|

However, I think this is not quite working. I've attached (a tiny tar 
of) config and logs from `vpp0-3` in case somebody wants to double check.
Can somebody confirm that the paragraph Benoit mentioned works for them?

    OSPFv2 needs one IPv4 channel. OSPFv3 needs either one IPv6 channel,
    or one IPv4 channel (RFC 5838
    <http://www.rfc-editor.org/info/rfc5838>). Therefore, it is possible
    to use OSPFv3 for both IPv4 and Pv6 routing, but it is necessary to
    have two protocol instances anyway. If no channel is configured,
    appropriate channel is defined with default parameters.



groet,
Pim
-- 

Pim van Pelt
PBVP1-RIPE -https://ipng.ch/
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