strongSwan IPsec Configuration via UCI

Linux Charon IPsec daemon can be configured through /etc/config/ipsec.

Note: this has been updated to the swanctl-based configuration, and is current as of 5.9.5 packaging. For previous versions, use the Wiki's page history functionality.

Type	Name	Type	Required	Default	Description
option	zone	string	no	vpn	Firewall zone. Has to match the defined firewall zone
list	listen	string	yes	(none)	Interface that accept VPN traffic (empty for all interfaces, multiple lines for several interfaces)
option	debug	number	no	0	Trace level: 0 is least verbose, 4 is most - logs visible from output of logread -f

Contains tunnel definition.

Name	Type	Required	Default	Description
enabled	boolean	yes	(none)	Configuration is enabled or not
gateway	ipaddr	yes	(none)	IP address or FQDN name of the tunnel remote endpoint, or permitted subnets that peers can initiate this configuration from (analogue to local_leftip)
local_gateway	ipaddr	no	(none)	IP address or FQDN of the tunnel local endpoint
local_sourceip	ipaddr	no	(none)	Virtual IP(s) to request in IKEv2 configuration payloads requests, or in IKEv1 mode config (enables sending them/initiating it instead of quick mode)
local_ip	ipaddr	no	(none)	Local address(es) to use in IKE negotiation when initiating; for responding, enumerates addresses we can negotiate from (and may by subnets or CIDRs)
local_identifier	string	no	(none)	Local identifier for IKE (phase 1)
remote_identifier	string	no	(none)	Remote identifier for IKE (phase 1)
authentication_method	string	yes	(none)	IKE authentication (phase 1). Only allowed value ath the moment is psk
pre_shared_key	string	no	(none)	The preshared key for the tunnel if authentication is psk
crypto_proposal	list	yes	(none)	List of IKE (phase 1) proposals to use for authentication (see below)
tunnel	list	yes	(none)	Name of ESP/AH (phase 2) section (see below)
keyingretries	integer	no	3	Number of retransmissions to attempt during initial negotiation
dpddelay	interval	no	30s	Liveness interval for IKE
inactivity	interval	no	(none)	Interval before closing an inactive CHILD_SA
fragmentation	string	no	yes	Use IKE fragmentation (maybe “yes”, “accept”, “force”, or “no”)
mobike	string	no	yes	Enable MOBIKE on IKEv2
local_cert	string	no	(none)	List of cert pathnames to use for authentication
local_key	string	no	(none)	List of private key pathnames to use with above certificates
ca_cert	string	no	(none)	List of names of CA certificates that need to lie in remote peer's certificate's path of trust
rekeytime	interval	no	(none)	IKEv2 interval to refresh keying material; also used to compute lifetime
overtime	interval	no	(none)	Limit on time to complete rekeying/reauthentication (defaults to 10% of rekeytime)
keyexchange	string	no	ikev2	Version of IKE to negotiation (“ikev1”, “ikev2”, or “ike” for both)

Definition of encryption proposals. Derived from strongSwan cipher suites

Name	Type	Required	Default	Description
encryption_algorithm	string	yes	(none)	Encryption method (aes128, aes192, aes256, 3des)
hash_algorithm	string	yes	(none)	Hash algorithm (md5, sha1, sha2, ...) not permitted when an AEAD algorithm is used
dh_group	string	yes	(none)	Diffie-Hellman exponentiation (modp768, modp1024, ...)
prf_algorithm	string	no	(none)	Pseudo-Random Functions to use with IKE (prfmd5, prfsha1, prfsha256, ...); not applicable to ESP

Contains network defintion per tunnel.

Name	Type	Required	Default	Description
local_subnet	list	yes	(none)	Local network(s) one per line
remote_subnet	list	yes	(none)	Remote network(s) one per line
local_nat	subnet	no	(none)	NAT range for tunnels with overlapping IP addresses
crypto_proposal	list	yes	(none)	List of ESP (phase two) proposals
startaction	string	no	route	Action on initial configuration load (none, start, route)
updown	string	no	(none)	Path to script to run on CHILD_SA up/down events
lifetime	interval	no	(none)	Maximum duration of the CHILD_SA before closing (defaults to 110% of rekeytime)
rekeytime	interval	no	(none)	Duration of the CHILD_SA before rekeying
dpdaction	string	no	(none)	Action done when DPD timeout occurs (may be “none”, “clear”, “hold”, “restart”, “trap”, or “start”)
closeaction	string	no	route	Action done when CHILD_SA is closed (may be “add”, “route”, “start”, “none”, or “trap”)
if_id	string	no	(none)	XFRM interface ID set on input and output interfaces (should be coordinated with “ifid” values in route entries on “xfrm” interfaces)
priority	string	no	(none)	Priority of the CHILD_SA
ipcomp	bool	no	false	Enable ipcomp compression
hw_offload	bool	no	false	Enable H/W offload

Local configuration for /etc/config/ipsec:

config 'ipsec'
  # useful so traffic isn't sourced from internal addresses,
  # which would then requiring NATting and port 4500, etc.
  list 'interface' 'wan'
  option 'zone' 'vpn'
 
config 'remote' 'acme'
  option 'enabled' '1'
  # address of wan device
  option 'local_ip' '6.6.6.6'
  # peer has routable DHCP'd address which changes
  option 'gateway' 'any'
  option 'authentication_method' 'pubkey'
  option 'local_identifier' 'C=US, O=Acme Corporation, CN=headquarters'
  option 'remote_identifier' 'C=US, O=Acme Corporation, CN=soho'
  option 'local_cert' 'headquarters.crt'
  option 'local_key' 'headquarters.key'
  option 'ca_cert' 'acme.crt'
  option 'rekeytime' '4h'
  option 'keyingretries' '0'
  option 'mobike' '0'
  option 'fragmentation' '1'
  list   'crypto_proposal' 'ike_proposal'
  list   'tunnel' 'tun_soho'
 
config 'crypto_proposal' 'ike_proposal'
  option 'encryption_algorithm' 'aes256gcm'
  # no hash_algorithm allowed with AEAD
  option 'dh_group' 'modp3072'
  option prf_algorithm 'prfsha512'
 
# we don't specify subnets because we're going to use XFRM-interfaced based routes instead
config 'tunnel' 'tun_soho'
  list   'local_subnet' '0.0.0.0/0'
  list   'remote_subnet' '0.0.0.0/0'
  option 'if_id' '357'
  option 'rekeytime' '1h'
  # other end is behind NAT or we'd use 'route' to initiate
  option 'startaction' 'none'
  option 'closeaction' 'none'
  list   'crypto_proposal' 'esp_proposal'
 
config 'crypto_proposal' 'esp_proposal'
  option 'encryption_algorithm' 'aes256gcm'
  # no hash_algorithm with allowed with AEAD
  option 'dh_group' 'modp3072'

and to support XFRM-based interfaces with associated routing, we put the following into /etc/config/network:

config 'interface' 'xfrm0'
  option 'ifid' '357'
  option 'tunlink' 'wan'
  option 'mtu' '1438'
  option 'zone' 'vpn'
  option 'proto' 'xfrm'
  # useful if you want to run Bonjour/mDNS across VPN tunnels
  option 'multicast' 'true'
 
config 'interface' 'xfrm0_s'
  option 'ifname' '@xfrm0'
  option 'proto' 'static'
  option 'ipaddr' '192.168.254.1/30'
 
config 'route'
  option 'interface' 'xfrm0'
  option 'target' '192.168.10.0/24'
  option 'source' '192.168.1.1'

Lastly, /etc/config/firewall requires:

config 'zone'
  option 'name' 'vpn'
  option 'network' 'xfrm0'
  option 'input' 'ACCEPT'
  option 'output' 'ACCEPT'
  option 'forward' 'ACCEPT'
  option 'mtu_fix' '1'
 
config 'forwarding'
  option 'src' 'lan'
  option 'dest' 'vpn'
 
config 'forwarding'
  option 'src' 'vpn'
  option 'dest' 'lan'
 
config 'rule'
  option 'name' 'Allow-IPSec-ESP'
  option 'src' 'wan'
  option 'proto' 'esp'
  option 'family' 'ipv4'
  option 'target' 'ACCEPT'
 
config 'rule'
  option 'name' 'Allow-ISP-ISAKMP'
  option 'src' 'wan'
  option 'src_port' '500'
  option 'dest_port' '500'
  option 'proto' 'udp'
  option 'family' 'ipv4'
  option 'target' 'ACCEPT'

Lastly generate the certificates for both ends on the hub:

root@HQ:~# gencerts -s US acme.com "Acme Corporation" headquarters soho
Generated as headquarters-certs.tar.gz
Generated as soho-certs.tar.gz
root@HQ:~# tar ztvf headquarters-certs.tar.gz 
-r--r--r-- 0/0      1870 2021-06-17 19:01:38 swanctl/x509ca/acme.crt
-r--r--r-- 0/0      1923 2021-06-17 19:01:53 swanctl/x509/headquarters.crt
-r-------- 0/0      3243 2021-06-17 19:01:53 swanctl/private/headquarters.key
root@HQ:~# tar ztvf soho-certs.tar.gz 
-r--r--r-- 0/0      1870 2021-06-17 19:01:38 swanctl/x509ca/acme.crt
-r--r--r-- 0/0      1903 2021-06-17 19:02:04 swanctl/x509/soho.crt
-r-------- 0/0      3243 2021-06-17 19:02:04 swanctl/private/soho.key
root@HQ:~#

Note that the filenames in headquarters.tar.gz correspond to local_cert, local_key, and ca_cert above. Similarly, the certificate's subject corresponds to the local_identifier:

root@HQ:~# openssl x509 -in /etc/swanctl/x509/headquarters.crt -noout -subject
subject=C = US, O = Acme Corporation, CN = headquarters
root@OpenWrt2:~#

As these files are present on the headquarters firewall already, you can remove headquarters.tar.gz. You can also remove:

/etc/swanctl/x509/soho.crt
/etc/swanctl/private/soho.key

as these are only needed on the remote end (SoHo).

Now copy the soho-certs.tar.gz file over to the SoHo router, and unpack it with:

root@SoHo:~# tar -zxf soho-certs.tar.gz -C /etc

Lastly, configure /etc/config/ipsec on the SoHo router:

config 'ipsec'
  option 'zone' 'vpn'
  listen 'interface' 'wan'
 
config 'remote' 'headquarters'
  option 'enabled' '1'
  option 'local_ip' '%any'
  option 'gateway' '6.6.6.6'
  option 'local_identifier' 'C=US, O=Acme Corporation, CN=soho'
  option 'remote_identifier' 'C=US, O=Acme Corporation, CN=headquarters'
  option 'authentication_method' 'pubkey'
  option 'fragmentation' '1'
  option 'local_cert' 'soho.crt'
  option 'local_key' 'soho.key'
  option 'ca_cert' 'acme.crt'
  option 'rekeytime' '4h'
  option 'keyingretries' '0'
  option 'mobike' 0
  list 'crypto_proposal' 'ike_proposal'
  list 'tunnel' 'tun_headquarters'
 
config 'crypto_proposal' 'ike_proposal'
  option 'encryption_algorithm' 'aes256gcm128'
  # no hash_algorithm allowed with AEAD
  option 'dh_group' 'modp3072'
  option 'prf_algorithm' 'prfsha512'
 
config tunnel 'tun_headquarters'
  list   'local_subnet' '0.0.0.0/0'
  list   'remote_subnet' '0.0.0.0/0'
  option 'if_id' '308'
  option 'rekeytime' '1h'
  option 'startaction' 'trap'
  option 'closeaction' 'none'
  option 'dpdaction' 'restart'
  list 'crypto_proposal' 'esp_proposal'
 
config 'crypto_proposal' 'esp_proposal'
  option 'encryption_algorithm' 'aes256gcm128'
  # no hash_algorithm allowed with AEAD
  option 'dh_group' 'modp3072'

Now modify /etc/config/firewall as above, and /etc/config/network as:

config 'interface' 'xfrm0'
  option 'ifid' '308'
  option 'tunlink' 'wan'
  option 'mtu' '1438'
  option 'zone' 'vpn'
  option 'proto' 'xfrm'
  # useful if you want to run Bonjour/mDNS across VPN tunnels
  option 'multicast' 'true'
 
config 'interface' 'xfrm0_s'
  option 'ifname' '@xfrm0'
  option 'proto' 'static'
  option 'ipaddr' '192.168.254.2/30'
 
config 'route'
  option 'interface' 'xfrm0'
  option 'target' '192.168.1.0/24'
  # assuming lan has the address 192.168.10.1/24
  option 'source' '192.168.10.1'

And when this is all done, on both ends do:

root@HQ:~# /etc/init.d/swanctl enable
root@HQ:~# /etc/init.d/swanctl restart

strongSwan IPsec Configuration via UCI

Sections

ipsec

remote

crypto_proposal

tunnel