"Configuring IPSec" - пошаговое руководство по настройке IPSec тунеля на FreeBSD (с использованем Racoon IKE демона).

Ниже, краткий пересказ:

Ядро:
  options		IPSEC
  options		IPSEC_ESP
  options		IPSEC_DEBUG
  pseudo-device	gif

Ставим для управления секретными ключами - Racoon IKE:
  cd /usr/ports/security/racoon
  make install clean
  vi /usr/local/etc/racoon/racoon.conf

path include "/usr/local/etc/racoon" ;
path pre_shared_key "/usr/local/etc/racoon/psk.txt" ;
# "log" specifies logging level.  It is followed by either "notify", "debug"
# or "debug2".
#log debug;

# "padding" defines some parameter of padding.  You should not touch these.
padding
{
	maximum_length 20;	# maximum padding length.
	randomize off;		# enable randomize length.
	strict_check off;	# enable strict check.
	exclusive_tail off;	# extract last one octet.
}

# if no listen directive is specified, racoon will listen to all
# available interface addresses.
listen
{
	isakmp A.A.A.A [500];
}

# Specification of default various timer.
timer
{
	# These value can be changed per remote node.
	counter 5;		# maximum trying count to send.
	interval 20 sec;	# maximum interval to resend.
	persend 1;		# the number of packets per a send.

	# timer for waiting to complete each phase.
	phase1 30 sec;
	phase2 15 sec;
}

remote B.B.B.B
{
	#exchange_mode main,aggressive;
	exchange_mode aggressive,main;
	doi ipsec_doi;
	situation identity_only;

	nonce_size 16;
	lifetime time 60 min;	# sec,min,hour
	initial_contact on;
	support_mip6 on;
	proposal_check obey;	# obey, strict or claim

	proposal {
		encryption_algorithm blowfish;
		hash_algorithm sha1;
		authentication_method pre_shared_key ;
		dh_group 5 ;
	}
}

sainfo B.B.B.B
{
	pfs_group 5;
	lifetime time 24 hour;
	encryption_algorithm blowfish ;
	authentication_algorithm hmac_sha1;
	compression_algorithm deflate ;
}

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

Запускаем Racoon:
  /usr/local/sbin/racoon -f /usr/local/etc/racoon/racoon.conf -l

Поднимаем маршрутизацию:
   /sbin/route add -net 192.168.1.0/24 10.0.0.1
  /sbin/route add -net 10.0.0.0/8 192.168.1.1

Правим /etc/rc.conf
  ipsec_enable="YES"
  ipsec_file="/etc/ipsec.conf"
  gif_interfaces="gif0"
  ifconfig_gif0="10.0.0.1 netmask 255.0.0.0 192.168.1.1 netmask 255.255.255.0"
  gifconfig_gif0="A.A.A.A netmask 255.255.240.0 B.B.B.B netmask 255.255.240.0"


Настраиваем параметры для setkey (man setkey), для управления IPsec SA/SP базой.
  vi /etc/ipsec.conf

flush;
spdflush;
#add the policy to the SPD database
spdadd 10.0.0.0/8 192.168.1.0/24 any -P out ipsec
esp/tunnel/A.A.A.A-B.B.B.B/require;

spdadd 192.168.1.0/24 10.0.0.0/8 any -P in ipsec
esp/tunnel/B.B.B.B-A.A.A.A/require;