OpenBSD /etc/ipsec.conf for AWS VPC VPN

ike esp from $OPENBSD_NETWORK/MASK to $VPC_NETWORK/MASK \
        local $LOCAL_PUBLIC_IP peer $TUNNEL1_IP \
        main auth hmac-sha1 enc aes group modp1024 lifetime $PHASE1_LIFETIME \
        quick auth hmac-sha1 enc aes group modp1024 lifetime $PHASE2_LIFETIME \
        srcid $LOCAL_PUBLIC_IP \
        psk "$TUNNEL1_PSK" \
        tag amazon-vpc
ike esp from $OPENBSD_NETWORK/MASK to $VPC_NETWORK/MASK \
        local $LOCAL_PUBLIC_IP peer $TUNNEL2_IP \
        main auth hmac-sha1 enc aes group modp1024 lifetime $PHASE1_LIFETIME \
        quick auth hmac-sha1 enc aes group modp1024 lifetime $PHASE2_LIFETIME \
        srcid $LOCAL_PUBLIC_IP \
        psk "$TUNNEL2_PSK" \
        tag amazon-vpc

! Amazon Web Services
! Virtual Private Cloud
!
! AWS utilizes unique identifiers to manipulate the configuration of 
! a VPN Connection. Each VPN Connection is assigned an identifier and is 
! associated with two other identifiers, namely the 
! Customer Gateway Identifier and Virtual Private Gateway Identifier.
!
! Your VPN Connection ID                  : vpn-0example
! Your Virtual Private Gateway ID         : vgw-1example
! Your Customer Gateway ID                : cgw-2example
!
!
! This configuration consists of two tunnels. Both tunnels must be 
! configured on your Customer Gateway. Only a single tunnel will be up at a 
! time to the VGW.
! 
! You may need to populate these values throughout the config based on your setup:
! <outside_interface> - External interface of the ASA
! <outside_access_in> - Inbound ACL on the external interface
! <amzn_vpn_map> - Outside crypto map
! <vpc_subnet> and <vpc_subnet_mask> - VPC address range
! <local_subnet> and <local_subnet_mask> - Local subnet address range
! <sla_monitor_address> - Target address that is part of acl-amzn to run SLA monitoring

! --------------------------------------------------------------------------------
! IPSec Tunnels
! --------------------------------------------------------------------------------
! #1: Internet Key Exchange (IKE) Configuration
!
! A policy is established for the supported ISAKMP encryption, 
! authentication, Diffie-Hellman, lifetime, and key parameters.
!
! Note that there are a global list of ISAKMP policies, each identified by 
! sequence number. This policy is defined as #201, which may conflict with
! an existing policy using the same or lower number depending on 
! the encryption type. If so, we recommend changing the sequence number to 
! avoid conflicts and overlap.
!
crypto isakmp identity address 
crypto isakmp enable <outside_interface>
crypto isakmp policy 201
  encryption aes
  authentication pre-share
  group 2
  lifetime $PHASE1_LIFETIME
  hash sha
exit
!
! The tunnel group sets the Pre Shared Key used to authenticate the 
! tunnel endpoints.
!
tunnel-group $TUNNEL1_IP type ipsec-l2l
tunnel-group $TUNNEL1_IP ipsec-attributes
   pre-shared-key $TUNNEL1_PSK
!
! This option enables IPSec Dead Peer Detection, which causes periodic
! messages to be sent to ensure a Security Association remains operational.
!
   isakmp keepalive threshold 10 retry 3
exit
!
tunnel-group $TUNNEL2_IP type ipsec-l2l
tunnel-group $TUNNEL2_IP ipsec-attributes
   pre-shared-key $TUNNEL2_PSK
!
! This option enables IPSec Dead Peer Detection, which causes periodic
! messages to be sent to ensure a Security Association remains operational.
!
   isakmp keepalive threshold 10 retry 3
exit

! --------------------------------------------------------------------------------
! #2: Access List Configuration
!
! Access lists are configured to permit creation of tunnels and to send applicable traffic over them.
! This policy may need to be applied to an inbound ACL on the outside interface that is used to manage control-plane traffic. 
! This is to allow VPN traffic into the device from the Amazon endpoints.
!
access-list <outside_access_in> extended permit ip host $TUNNEL1_IP host $LOCAL_PUBLIC_IP
access-list <outside_access_in> extended permit ip host $TUNNEL2_IP host $LOCAL_PUBLIC_IP
! The following access list named acl-amzn specifies all traffic that needs to be routed to the VPC. Traffic will
! be encrypted and transmitted through the tunnel to the VPC. Association with the IPSec security association
! is done through the "crypto map" command.
!
! This access list should contain a static route corresponding to your VPC CIDR and allow traffic from any subnet.
! If you do not wish to use the "any" source, you must use a single access-list entry for accessing the VPC range.
! If you specify more than one entry for this ACL without using "any" as the source, the VPN will function erratically.
! The any rule is also used so the security association will include the ASA outside interface where the SLA monitor
! traffic will be sourced from.
! See section #4 regarding how to restrict the traffic going over the tunnel
!
!
access-list acl-amzn extended permit ip any <vpc_subnet> <vpc_subnet_mask>

!---------------------------------------------------------------------------------
! #3: IPSec Configuration
!
! The IPSec transform set defines the encryption, authentication, and IPSec
! mode parameters.
!
crypto ipsec transform-set transform-amzn esp-aes esp-sha-hmac
! The crypto map references the IPSec transform set and further defines
! the Diffie-Hellman group and security association lifetime. The mapping is created
! as #1, which may conflict with an existing crypto map using the same
! number. If so, we recommend changing the mapping number to avoid conflicts.
!
crypto map <amzn_vpn_map> 1 match address acl-amzn
crypto map <amzn_vpn_map> 1 set pfs group2
crypto map <amzn_vpn_map> 1 set peer  $TUNNEL1_IP $TUNNEL2_IP
crypto map <amzn_vpn_map> 1 set transform-set transform-amzn
!
! Only set this if you do not already have an outside crypto map, and it is not applied:
!
crypto map <amzn_vpn_map> interface <outside_interface>
!
! Additional parameters of the IPSec configuration are set here. Note that
! these parameters are global and therefore impact other IPSec
! associations.
! Set security association lifetime until it is renegotiated.
crypto ipsec security-association lifetime seconds $PHASE2_LIFETIME
!
! This option instructs the firewall to clear the "Don't Fragment"
! bit from packets that carry this bit and yet must be fragmented, enabling
! them to be fragmented.
!
crypto ipsec df-bit clear-df <outside_interface>
!
! This configures the gateway's window for accepting out of order
! IPSec packets. A larger window can be helpful if too many packets
! are dropped due to reordering while in transit between gateways.
!
crypto ipsec security-association replay window-size 128
!
! This option instructs the firewall to fragment the unencrypted packets
! (prior to encryption).
!
crypto ipsec fragmentation before-encryption <outside_interface>
!
! This option causes the firewall to reduce the Maximum Segment Size of
! TCP packets to prevent packet fragmentation.
sysopt connection tcpmss 1387
!
! In order to keep the tunnel in an active or always up state, the ASA needs to send traffic to the subnet
! defined in acl-amzn. SLA monitoring can be configured to send pings to a destination in the subnet and
! will keep the tunnel active. This traffic needs to be sent to a target that will return a response.
! This can be manually tested by sending a ping to the target from the ASA sourced from the outside interface.
! A possible destination for the ping is an instance within the VPC. For redundancy multiple SLA monitors 
! can be configured to several instances to protect against a single point of failure.
!
! The monitor is created as #1, which may conflict with an existing monitor using the same
! number. If so, we recommend changing the sequence number to avoid conflicts.
!
sla monitor 1
   type echo protocol ipIcmpEcho <sla_monitor_address> interface <outside_interface>
   frequency 5
exit
sla monitor schedule 1 life forever start-time now
!
! The firewall must allow icmp packets to use "sla monitor" 
icmp permit any <outside_interface>

!---------------------------------------------------------------------------------------
! #4: VPN Filter
! The VPN Filter will restrict traffic that is permitted through the tunnels. By default all traffic is denied.
! The first entry provides an example to include traffic between your VPC Address space and your office.
! You may need to run 'clear crypto isakmp sa', in order for the filter to take effect.
!
! access-list amzn-filter extended permit ip <vpc_subnet> <vpc_subnet_mask> <local_subnet> <local_subnet_mask>
access-list amzn-filter extended deny ip any any
group-policy filter internal
group-policy filter attributes
vpn-filter value amzn-filter
tunnel-group $TUNNEL1_IP general-attributes
default-group-policy filter
exit
tunnel-group $TUNNEL2_IP general-attributes
default-group-policy filter
exit

!---------------------------------------------------------------------------------------
! #5: NAT Exemption
! If you are performing NAT on the ASA you will have to add a nat exemption rule.
! This varies depending on how NAT is set up.  It should be configured along the lines of:
! object network obj-SrcNet
!   subnet 0.0.0.0 0.0.0.0
! object network obj-amzn
!   subnet <vpc_subnet> <vpc_subnet_mask>
! nat (inside,outside) 1 source static obj-SrcNet obj-SrcNet destination static obj-amzn obj-amzn
! If using version 8.2 or older, the entry would need to look something like this:
! nat (inside) 0 access-list acl-amzn
! Or, the same rule in acl-amzn should be included in an existing no nat ACL.
!
!---------------------------------------------------------------------------------------
!  Additional Notes and Questions
!  - Amazon Virtual Private Cloud Getting Started Guide: 
!       http://docs.amazonwebservices.com/AmazonVPC/latest/GettingStartedGuide
!  - Amazon Virtual Private Cloud Network Administrator Guide: 
!       http://docs.amazonwebservices.com/AmazonVPC/latest/NetworkAdminGuide
!  - Troubleshooting Cisco ASA Customer Gateway Connectivity:
!       http://docs.amazonwebservices.com/AmazonVPC/latest/NetworkAdminGuide/Cisco_ASA_Troubleshooting.html
!  - XSL Version: 2009-07-15-1119716