strongswan: What is the difference between left and leftid?

Question

This tutorial use left parameter when setup strongswan, while this tutorial also use leftid parameter. What is the difference between left and leftid?

Answer 1

Found answer from here:

One defines the local IP address(es), `left`, which does not have to be specified
unless it should be restricted. The other, `leftid`, the local identity used during
authentication, which will default to the local IP address or the subject DN of the
local certificate, if one is configured.

Note that the convention is to use `left...` options for local settings and `right...` for
those of the remote, but they might get swapped if an IP in `right` is found locally.

Please refer to the man page for ipsec.conf (`man ipsec.conf`) or the [wiki page for 
the conn section][1] for details.

----

You can't set `left` to an IP address that's not installed on any local interface. As you
can see in the log, the daemon won't be able to send packets from that address. 
Likewise, inbound request are dropped because the destination address doesn't match
the config (the `no IKE config found for ...` message). So either don't configure it (same 
as setting it to `%any`) or configure a local address from/on which packets can be 
sent/received (e.g. `172.30.13.1` in your case).


  [1]: https://wiki.strongswan.org/projects/strongswan/wiki/Connsection