Both:
conn %default
	ikelifetime=60m
	keylife=20m
	rekeymargin=3m
	keyingtries=1
	authby=secret
	keyexchange=ikev2
	mobike=no


--------------------------------------------------------

Node v5141:
conn quicknet-availo
        left=1.2.3.4
        leftsubnet=172.16.0.0/16
        leftid=@v5141
	leftfirewall=yes
        right=4.3.2.1
        rightsubnet=10.0.0.0/8
        rightid=@v6116
	forceencaps=yes
        auto=add

--------------------------------------------------------

Node v6116:
conn quicknet-availo
	left=4.3.2.1
	leftsubnet=10.0.0.0/8
	leftid=@v6116
	leftfirewall=yes
	right=1.2.3.4
	rightsubnet=172.16.0.0/16
	rightid=@v5141
	forceencaps=yes
	auto=add

--------------------------------------------------------

root@v5141: ~ #> ipsec statusall
Status of IKE charon daemon (strongSwan 5.1.2, Linux 3.13.0-61-generic, x86_64):
  uptime: 79 minutes, since Jul 30 14:33:22 2015
  malloc: sbrk 2433024, mmap 0, used 346928, free 2086096
  worker threads: 11 of 16 idle, 5/0/0/0 working, job queue: 0/0/0/0, scheduled: 2
  loaded plugins: charon test-vectors aes rc2 sha1 sha2 md4 md5 random nonce x509 revocation constraints pkcs1 pkcs7 pkcs8 pkcs12 pem openssl xcbc cmac hmac ctr ccm gcm attr kernel-netlink resolve socket-default stroke updown eap-identity addrblock
Listening IP addresses:
  1.2.3.4
Connections:
quicknet-availo:  1.2.3.4...4.3.2.1  IKEv2
quicknet-availo:   local:  [v5141] uses pre-shared key authentication
quicknet-availo:   remote: [v6116] uses pre-shared key authentication
quicknet-availo:   child:  172.16.0.0/16 === 10.0.0.0/8 TUNNEL
Security Associations (1 up, 0 connecting):
quicknet-availo[4]: ESTABLISHED 21 minutes ago, 1.2.3.4[v5141]...4.3.2.1[v6116]
quicknet-availo[4]: IKEv2 SPIs: fdd39a4062ab8d16_i 9db30a609e063eb7_r*, pre-shared key reauthentication in 33 minutes
quicknet-availo[4]: IKE proposal: AES_CBC_128/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_2048
quicknet-availo{4}:  INSTALLED, TUNNEL, ESP in UDP SPIs: ca25ba32_i c9265656_o
quicknet-availo{4}:  AES_CBC_128/HMAC_SHA1_96, 0 bytes_i, 468 bytes_o (6 pkts, 279s ago), rekeying in 7 minutes
quicknet-availo{4}:   172.16.0.0/16 === 10.0.0.0/8

root@v5141: ~ #> ip route list table 220
root@v5141: ~ #>
root@v5141: ~ #> ip xfrm policy
src 10.0.0.0/8 dst 172.16.0.0/16
	dir fwd priority 1923
	tmpl src 4.3.2.1 dst 1.2.3.4
		proto esp reqid 4 mode tunnel
src 10.0.0.0/8 dst 172.16.0.0/16
	dir in priority 1923
	tmpl src 4.3.2.1 dst 1.2.3.4
		proto esp reqid 4 mode tunnel
src 172.16.0.0/16 dst 10.0.0.0/8
	dir out priority 1923
	tmpl src 1.2.3.4 dst 4.3.2.1
		proto esp reqid 4 mode tunnel

root@v6116: ~ #> ipsec up quicknet-availo
initiating IKE_SA quicknet-availo[3] to 1.2.3.4
generating IKE_SA_INIT request 0 [ SA KE No N(NATD_S_IP) N(NATD_D_IP) ]
sending packet: from 4.3.2.1[500] to 1.2.3.4[500] (1212 bytes)
received packet: from 1.2.3.4[500] to 4.3.2.1[500] (440 bytes)
parsed IKE_SA_INIT response 0 [ SA KE No N(NATD_S_IP) N(NATD_D_IP) N(MULT_AUTH) ]
remote host is behind NAT
authentication of 'v6116' (myself) with pre-shared key
establishing CHILD_SA quicknet-availo
generating IKE_AUTH request 1 [ IDi N(INIT_CONTACT) IDr AUTH SA TSi TSr N(MULT_AUTH) N(EAP_ONLY) ]
sending packet: from 4.3.2.1[4500] to 1.2.3.4[4500] (380 bytes)
received packet: from 1.2.3.4[4500] to 4.3.2.1[4500] (220 bytes)
parsed IKE_AUTH response 1 [ IDr AUTH SA TSi TSr N(AUTH_LFT) ]
authentication of 'v5141' with pre-shared key successful
IKE_SA quicknet-availo[3] established between 4.3.2.1[v6116]...1.2.3.4[v5141]
scheduling reauthentication in 3325s
maximum IKE_SA lifetime 3505s
CHILD_SA quicknet-availo{3} established with SPIs c98d9ef0_i c7e79260_o and TS 10.0.0.0/8 === 172.16.0.0/16
connection 'quicknet-availo' established successfully