dco: `ping` option does not work unless either `ping-restart` or `ping-exit` is present

[LGA1150]

In a P2P config with a ping option but without ping-restart or ping-exit, DCO does not ping the remote. It works only after disabling DCO.

[ordex]

It seems this is a control channel feature (different from keepalive)?
Therefore this is an issue with the userspace program. I am moving this ticket to the right repo

[cron2]

--ping without --ping-restart is likely just not implemented in DCO... that is only half of what --keepalive does (arm both: outgoing packets and setup a keepalive timer on incoming packets).

Not sure if this is a relevant scenario for anything...

[cron2]

@ordex

       --keepalive args
              A helper directive designed to simplify the expression of --ping
              and --ping-restart.
..

              For example, --keepalive 10 60 expands as follows:

                 if mode server:
                     ping 10                    # Argument: interval
                     ping-restart 120           # Argument: timeout*2
                     push "ping 10"             # Argument: interval
                     push "ping-restart 60"     # Argument: timeout
                 else
                     ping 10                    # Argument: interval
                     ping-restart 60            # Argument: timeout

[ordex]

@LGA1150 can you clarify how ping without ping-restart is any useful?
Personally I have only seen config files using keepalive

[ordex]

For the very same reason, DCO right now expects a TIMEOUT next to the sending INTERVAL:

 257         if ((attrs[OVPN_A_PEER_KEEPALIVE_INTERVAL] &&
 258              !attrs[OVPN_A_PEER_KEEPALIVE_TIMEOUT]) ||
 259             (!attrs[OVPN_A_PEER_KEEPALIVE_INTERVAL] &&
 260              attrs[OVPN_A_PEER_KEEPALIVE_TIMEOUT])) {
 261                 NL_SET_ERR_MSG_FMT_MOD(info->extack,
 262                                        "keepalive interval and timeout are required together");
 263                 return -EINVAL;
 264         }

[LGA1150]

can you clarify how ping without ping-restart is any useful? Personally I have only seen config files using keepalive

ping without ping-restart works like Wireguard's persistent-keepalive, i.e. a peer behind NAT sends packet periodically to keep the NAT session valid and the endpoint does not need to respond.

[ordex]

so basically you'll have only one endpoint sending the ping? does it mean on the other side you have only ping-restart without ping?

[cron2]

To keep the NAT state current, ping on the client and nothing else anywhere else would do the job - so no ping-restart anywhere.

Floating would, of course, also do the job (NAT state expires, next outgoing packet does a new NAT state and updates the now-current IP+Port on the server) - but it will not help with "the VPN sits around idle all day, and you want to access it from the outside" when the NAT state expires.

[ordex]

so no ping-restart anywhere.

not needed, but at least the server knows when the UDP client is gone

[cron2]

so no ping-restart anywhere.

not needed, but at least the server knows when the UDP client is gone

True, but I guess that this is also not supported with DCO today...? ("just incoming timeout handling, no outgoing packets")