left=<ip>
left=%defaultroute
From the ipsec.conf manpage:
(required) the IP address of the left participant's pub- lic-network interface, in any form accepted by ipsec_ttoaddr(3) or one of several magic values. If it is %defaultroute, and the config setup section's, inter- faces specification contains %defaultroute, left will be filled in automatically with the local address of the default-route interface (as determined at IPsec startup time); this also overrides any value supplied for left- nexthop. (Either left or right may be %defaultroute, but not both.) The value %any signifies an address to be filled in (by automatic keying) during negotiation. The value %opportunistic signifies that both left and left- nexthop are to be filled in (by automatic keying) from DNS data for left's client. The values %group and %opportunisticgroup makes this a policy group conn: one that will be instantiated into a regular or opportunistic conn for each CIDR block listed in the policy group file with the same name as the conn.
