Cisco ASA Site to Site IKEv2 VPN Static to Dynamic

KB ID 0001602

Problem

Site to Site VPNs are easy enough, define some interesting traffic, tie that to a crypto map, that decides where to send the traffic, create some phase 1 and phase 2 policies, wrap the whole lot up in a tunnel-group, and you’re done! But there needs to be a ‘peer address‘ in the crypto map, and if one end of the VPN is on DHCP that address is likely to change, so you cant supply that?

The solution is quite simple, Cisco had to address this years ago when they had remote IPSec VPN clients, you use a Dynamic Cryptomap, and because you can’t have a tunnel group either, you use the DefaultL2LGroup, (this gets used when a specific IP address is not defined).

ASA-Static-To-Dynamic-VPN

Note: If you have many remote sites using DHCP why not consider configuring EZVPN instead?

Static IP ASA Config

Use the following, change the values in red, to suit your own requirements;

!
object network OBJ-MAIN-SITE-LAN
 subnet 192.168.1.0 255.255.255.0
!
object network OBJ-REMOTE-SITE-LAN
 subnet 192.168.2.0 255.255.255.0
!
access-list VPN-INTERESTING-TRAFFIC extended permit IP object OBJ-MAIN-SITE-LAN object OBJ-REMOTE-SITE-LAN
nat (inside,outside) source static OBJ-MAIN-SITE-LAN OBJ-MAIN-SITE-LAN destination static OBJ-REMOTE-SITE-LAN OBJ-REMOTE-SITE-LAN
!
crypto ipsec IKEv2 ipsec-proposal IPSEC-PROP-1
 protocol esp encryption aes-256
 protocol esp integrity sha-1
!
crypto dynamic-map DMAP-VPN 10 set IKEv2 ipsec-proposal IPSEC-PROP-1
crypto dynamic-map DMAP-VPN 10 set reverse-route
!
crypto map outside_map 999 ipsec-isakmp dynamic DMAP-VPN
crypto map outside_map interface outside
!
crypto IKEv2 policy 2
 encryption aes-256
 integrity sha512
 group 24
 prf sha512
 lifetime seconds 86400
!
crypto IKEv2 enable outside
!
group-policy GP-SITE-2-SITE internal
group-policy GP-SITE-2-SITE attributes
 vpn-idle-timeout none
 vpn-session-timeout none
 vpn-filter none
 vpn-tunnel-protocol IKEv2 
tunnel-group DefaultL2LGroup general-attributes
 default-group-policy GP-SITE-2-SITE
tunnel-group DefaultL2LGroup ipsec-attributes
 IKEv2 remote-authentication pre-shared-key Password123
 IKEv2 local-authentication pre-shared-key Password123
!

Static IP ASA Config

As above, change the values in red, to suit your own requirements, (this is essentially just a normal site to site IKEv2 config!)

!
object network OBJ-REMOTE-SITE-LAN
 subnet 192.168.2.0 255.255.255.0
!
object network OBJ-MAIN-SITE-LAN
 subnet 192.168.1.0 255.255.255.0
!
access-list VPN-INTERESTING-TRAFFIC extended permit IP object OBJ-REMOTE-SITE-LAN object OBJ-MAIN-SITE-LAN
nat (inside,outside) source static OBJ-REMOTE-SITE-LAN OBJ-REMOTE-SITE-LAN destination static OBJ-MAIN-SITE-LAN OBJ-MAIN-SITE-LAN
!
crypto ipsec IKEv2 ipsec-proposal IPSEC-PROP-1
 protocol esp encryption aes-256
 protocol esp integrity sha-1
!
crypto map outside_map 1 match address VPN-INTERESTING-TRAFFIC
crypto map outside_map 1 set pfs group5
crypto map outside_map 1 set peer 1.1.1.1
crypto map outside_map 1 set IKEv2 ipsec-proposal IPSEC-PROP-1
crypto map outside_map interface outside
!
crypto IKEv2 policy 2
 encryption aes-256
 integrity sha512
 group 24
 prf sha512
 lifetime seconds 86400
!
crypto IKEv2 enable outside
!
group-policy GroupPolicy_1.1.1.1 internal
group-policy GroupPolicy_1.1.1.1 attributes
 vpn-tunnel-protocol IKEv2
tunnel-group 1.1.1.1 type ipsec-l2l
tunnel-group 1.1.1.1 general-attributes
 default-group-policy GroupPolicy_1.1.1.1
tunnel-group 1.1.1.1 ipsec-attributes
 IKEv2 remote-authentication pre-shared-key Password123
 IKEv2 local-authentication pre-shared-key Password123
!

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Author: PeteLong

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