crypto isakmp policy 1
  encr 3des
  authentication pre-share
  group 2
  lifetime 3600
crypto isakmp key YOURKEY address 10.20.30.42 no-xauth
!
!
crypto ipsec transform-set hostb-transform esp-3des esp-sha-hmac
  mode transport
!
crypto map hostb-cryptomap 1 ipsec-isakmp
  set peer 10.20.30.42
  set transform-set hostb-transform
  set pfs group2
  match address hostb-list
!
interface FastEthernet0/1
  ip address 10.20.30.40 255.255.255.0
  duplex auto
  speed auto
  crypto map hostb-cryptomap
!
ip access-list extended hostb-list
  permit ip host 10.20.30.40 host 10.20.30.42
!

apt-get install racoon ipsec-tools

#!/usr/sbin/setkey -f
 
flush;
spdflush;
 
spdadd 10.20.30.42 10.20.30.40 any -P out ipsec
  esp/transport//require;
 
spdadd 10.20.30.40 10.20.30.42 any -P in ipsec
  esp/transport//require;