Configuration Example of Dynamic IPsec Between a Statically Addressed ASA and a Dynamically Addressed IOS Router with NAT

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Updated:May 23, 2017

Document ID:211273

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Introduction

This document provides a sample configuration for how to enable the Adaptive Security Appliance (ASA ) in order to accept dynamic IPsec connections from the IOS Router.

Prerequisites

Requirements

Before you attempt this configuration, ensure that both the ASA and Router have Internet connectivity for establishing the IPsec tunnel.

This document assumes that you have already assigned the IP addresses on both the public and private interfaces and that you are able to ping the IP address of the remote VPN device.

Components Used

The information in this document is based on these software and hardware versions:

Cisco 2900 Router with Cisco IOS Software Release 15.2(4)M3
Cisco Adaptive Security Appliance Software version 9.4(1)

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

Refer to the Cisco Technical Tips Conventions for more information on document conventions.

Background Information

The remote router performs Network Address Translation (NAT) if private network 10.1.1.x accesses the Internet. Traffic from 10.1.1.x to private network 10.2.2.x behind the ASA is excluded from the NAT process. The IPsec tunnel establishes only if the traffic (10.1.1.x) initates the connection from the router with the ASA that has a remote network (10.2.2.x). The router can initiate connections to the ASA, but the ASA cannot initiate connections to the router.

This configuration enables the ASA to create a dynamic IPsec LAN-to-LAN (L2L) tunnel with a remote VPN router. This Router dynamically recieves its outside public IP address from its Internet service provider. Dynamic Host Configuration Protocol (DHCP) provides this mechanism in order to allocate IP addresses dynamically from the provider. This allows IP addresses to be reused when hosts no longer need them.

On the ASA you can configure a Manual NAT to ensure the traffic that goes through the tunnel does not get translated. In this example, if you are on the 10.2.2.0 network and go to the 10.1.1.0 network, the Manual NATis used to permit the 10.1.1.0 network traffic to be encrypted without being translated to the outside interface IP address. On the router, the route-map and access-list commands are used to permit the 10.1.1.0 network traffic to be encrypted without NAT. However, when you go anywhere else (like the Internet), you are translated to the outside interface IP address through Port Address Translation (PAT).

Note: Refer to Applying NAT for more information on NAT

These are the configuration commands required on the ASA in order for traffic not to run through PAT over the tunnel, and traffic to the Internet to run through PAT

object network LOCAL
 subnet 10.2.2.0 255.255.255.0
object network REMOTE
 subnet 10.1.1.0 255.255.255.0

nat (inside,outside) source static LOCAL LOCAL destination static REMOTE REMOTE

object network LOCAL
 nat (inside,outside) dynamic interface

Configure

In this section, you are presented with the information to configure the features described in this document.

Network Diagram

This document uses this network setup:

Configurations

This document uses these configurations:

Router

Router#show running-config
Current configuration : 1354 bytes
!
version 15.2
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Router
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
!
resource policy
!
ip cef


!--- Configuration for IKE policies.
!--- Enables the IKE policy configuration (config-isakmp) 
!--- command mode, where you can specify the parameters that 
!--- are used during an IKE negotiation.


crypto isakmp policy 1
 encryption aes 256
 hash sha
 authentication pre-share
 group 2


!--- Specifies the preshared key "cisco123" which should 
!--- be identical at both peers. This is a global 
!--- configuration mode command.


crypto isakmp key cisco123 address 192.168.1.2
!
!

!--- Configuration for IPsec policies.
!--- Enables the crypto transform configuration mode, 
!--- where you can specify the transform sets that are used 
!--- during an IPsec negotiation.


crypto ipsec transform-set myset esp-aes 256 esp-sha-hmac


!--- Indicates that IKE is used to establish 
!--- the IPsec Security Association for protecting the  
!--- traffic specified by this crypto map entry.


crypto map mymap 10 ipsec-isakmp


!--- Sets the IP address of the remote end.


 set peer 192.168.1.2


!--- Configures IPsec to use the transform-set 
!--- "myset" defined earlier in this configuration.


 set transform-set myset


!--- Specifies the interesting traffic to be encrypted.


 match address 101
!
!
!
!
interface FastEthernet0/0

!--- The interface dynamically learns its IP address 
!--- from the service provider.

 
 ip address DHCP 

 ip virtual-reassembly
 half-duplex

!--- Configures the interface to use the 
!--- crypto map "mymap" for IPsec.

 crypto map mymap
!
interface FastEthernet1/0
 no ip address
 shutdown
 duplex auto
 speed auto
!
interface Serial2/0
 ip address 10.1.1.2 255.255.255.0
 ip nat inside
 ip virtual-reassembly
 no fair-queue
!
interface Serial2/1
 no ip address
 shutdown
!
interface Serial2/2
 no ip address
 shutdown
!
interface Serial2/3
 no ip address
 shutdown
!
ip http server
no ip http secure-server
!
ip route 0.0.0.0 0.0.0.0 FastEthernet0/0
!
ip nat inside source route-map nonat interface FastEthernet0/0 overload
!

!--- This crypto ACL 101 -permit identifies the 
!--- matching traffic flows to be protected via encryption.


access-list 101 permit ip 10.1.1.0 0.0.0.255 10.2.2.0 0.0.0.255


!--- This ACL 110 identifies the traffic flows using route map and
!--- are PATed via outside interface (Ethernet0/0).


access-list 110 deny ip 10.1.1.0 0.0.0.255 10.2.2.0 0.0.0.255
access-list 110 permit ip 10.1.1.0 0.0.0.255 any


!
route-map nonat permit 10
 match ip address 110
!
!
control-plane
!

!
line con 0
line aux 0
line vty 0 4
!
!
end

ASA

ASA#show running-config 
ASA Version 9.4(1)
!
hostname ASA
enable password 8Ry2YjIyt7RRXU24 encrypted
names
!

!--- Configure the outside and inside interfaces.

interface GigabitEthernet0/0
 nameif outside
 security-level 0
 ip address 192.168.1.2 255.255.255.0
!
interface GigabitEthernet0/1
 nameif inside
 security-level 100
 ip address 10.2.2.1 255.255.255.0
!
!


!--- Output is suppressed.


!
passwd 2KFQnbNIdI.2KYOU encrypted
ftp mode passive


!--- Manual NAT prevents NAT for networks specified in the statement - nonat.
!--- The Object NAT 1 command specifies PAT using 
!--- the outside interface for all other traffic.

object network LOCAL
 subnet 10.2.2.0 255.255.255.0
object network REMOTE
 subnet 10.1.1.0 255.255.255.0


pager lines 24
mtu outside 1500
mtu inside 1500
no failover
no asdm history enable
arp timeout 14400


  
!--- Manual NAT prevents NAT for networks specified in the statement - nonat.
!--- The Object NAT 1 command specifies PAT using 
!--- the outside interface for all other traffic.



nat (inside,outside) source static LOCAL LOCAL destination static REMOTE REMOTE
!
object network LOCAL
 nat (inside,outside) dynamic interface

route outside 0.0.0.0 0.0.0.0 192.168.1.1 1

timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02
timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 mgcp-pat 0:05:00
timeout sip 0:30:00 sip_media 0:02:00 sip-invite 0:03:00 sip-disconnect 0:02:00
timeout uauth 0:05:00 absolute
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart


!--- PHASE 2 CONFIGURATION ---!
!--- The encryption types for Phase 2 are defined here.  


crypto ipsec ikev1 transform-set myset esp-aes-256 esp-sha-hmac


!--- Defines a dynamic crypto map with 
!--- the specified encryption settings.


crypto dynamic-map cisco 1 set ikev1 transform-set myset


!--- Binds the dynamic map to the IPsec/ISAKMP process.


crypto map dyn-map 10 ipsec-isakmp dynamic cisco


!--- Specifies the interface to be used with 
!--- the settings defined in this configuration.


crypto map dyn-map interface outside


!--- PHASE 1 CONFIGURATION ---!

!--- This configuration uses isakmp policy 10.   
!--- The configuration commands here define the Phase 
!--- 1 policy parameters that are used.

crypto ikev1 enable outside
crypto isakmp policy 10
 authentication pre-share
 encryption aes-256
 hash sha
 group 2
 lifetime 86400

!--- The security appliance provides the default tunnel groups
!--- for Lan to Lan access (DefaultL2LGroup) and configure the preshared key 
!--- (cisco123) to authenticate the remote router.  


tunnel-group DefaultL2LGroup ipsec-attributes
 pre-shared-key cisco123

telnet timeout 5
ssh timeout 5
console timeout 0
!
class-map inspection_default
 match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
 parameters
  message-length maximum 512
policy-map global_policy
 class inspection_default
  inspect dns preset_dns_map
  inspect ftp
  inspect h323 h225
  inspect h323 ras
  inspect netbios
  inspect rsh
  inspect rtsp
  inspect skinny
  inspect esmtp
  inspect sqlnet
  inspect sunrpc
  inspect tftp
  inspect sip
  inspect xdmcp
!
service-policy global_policy global
prompt hostname context
Cryptochecksum:6ed4a7bce392a439d0a16e86743e2663
: end

Clear Security Associations (SAs)

In the priviledge mode of the ASA, use these commands:

clear crypto ipsec sa—Deletes the active IPsec SAs. The keyword crypto is optional.
clear crypto isakmp sa—Deletes the active IKE SAs. The keyword crypto is optional.

Verify

Use this section to confirm that your configuration works properly.

The Cisco CLI Analyzer (registered customers only) supports certain show commands. Use the Cisco CLI Analyzer in order to view an analysis of show command output.

ASA Security Appliance - show Commands

show crypto isakmp sa—Shows all current IKE SAs at a peer.

ASA#show crypto isakmp sa

   Active SA: 1
    Rekey SA: 0 (A tunnel will report 1 Active and 1 Rekey SA during rekey)
Total IKE SA: 1

1   IKE Peer: 172.16.1.3
    Type    : L2L             Role    : responder
    Rekey   : no              State   : MM_ACTIVE

show crypto ipsec sa—Shows all current IPsec SAs at a peer.

ASA#show crypto ipsec sa
			interface: outside
    Crypto map tag: cisco, seq num: 1, local addr: 192.168.1.2

      local ident (addr/mask/prot/port): (10.2.2.0/255.255.255.0/0/0)
      remote ident (addr/mask/prot/port): (10.1.1.0/255.255.255.0/0/0)
      current_peer: 172.16.1.3

      #pkts encaps: 4, #pkts encrypt: 4, #pkts digest: 4
      #pkts decaps: 4, #pkts decrypt: 4, #pkts verify: 4
      #pkts compressed: 0, #pkts decompressed: 0
      #pkts not compressed: 4, #pkts comp failed: 0, #pkts decomp failed: 0
      #pre-frag successes: 0, #pre-frag failures: 0, #fragments created: 0
      #PMTUs sent: 0, #PMTUs rcvd: 0, #decapsulated frgs needing reassembly: 0
      #send errors: 0, #recv errors: 0

      local crypto endpt.: 192.168.1.2, remote crypto endpt.: 172.16.1.3

      path mtu 1500, ipsec overhead 58, media mtu 1500
      current outbound spi: 28C8C1BD

    inbound esp sas:
      spi: 0x33785672 (863524466)
         transform: esp-3des esp-md5-hmac
         in use settings ={L2L, Tunnel, }
         slot: 0, conn_id: 6, crypto-map: cisco
         sa timing: remaining key lifetime (kB/sec): (4274999/3564)
         IV size: 8 bytes
         replay detection support: Y
    outbound esp sas:
      spi: 0x28C8C1BD (684245437)
         transform: esp-3des esp-md5-hmac
         in use settings ={L2L, Tunnel, }
         slot: 0, conn_id: 6, crypto-map: cisco
         sa timing: remaining key lifetime (kB/sec): (4274999/3562)
         IV size: 8 bytes
         replay detection support: Y

Remote IOS Router - show Commands

show crypto isakmp sa—Shows all current IKE SAs at a peer.

Router#show crypto isakmp sa

   dst             src           state          conn-id slot status
192.168.1.2     172.16.1.3      QM_IDLE              1    0  ACTIVE

show crypto ipsec sa—Shows all current IPsec SAs at a peer.

Router#show crypto ipsec sa
		interface: Ethernet0/0
    Crypto map tag: pix, local addr 172.16.1.3

   protected vrf: (none)
   local  ident (addr/mask/prot/port): (10.1.1.0/255.255.255.0/0/0)
   remote ident (addr/mask/prot/port): (10.2.2.0/255.255.255.0/0/0)
   current_peer 192.168.1.2 port 500
     PERMIT, flags={origin_is_acl,}
    #pkts encaps: 4, #pkts encrypt: 4, #pkts digest: 4
    #pkts decaps: 4, #pkts decrypt: 4, #pkts verify: 4
    #pkts compressed: 0, #pkts decompressed: 0
    #pkts not compressed: 0, #pkts compr. failed: 0
    #pkts not decompressed: 0, #pkts decompress failed: 0
    #send errors 62, #recv errors 0

     local crypto endpt.: 172.16.1.3, remote crypto endpt.: 192.168.1.2
     path mtu 1500, ip mtu 1500, ip mtu idb Ethernet0/0
     current outbound spi: 0x33785672(863524466)

     inbound esp sas:
      spi: 0x28C8C1BD(684245437)
        transform: esp-3des esp-md5-hmac ,
        in use settings ={Tunnel, }
        conn id: 2002, flow_id: SW:2, crypto map: pix
        sa timing: remaining key lifetime (k/sec): (4431817/3288)
        IV size: 8 bytes
        replay detection support: Y
        Status: ACTIVE

     inbound ah sas:

     inbound pcp sas:

     outbound esp sas:
      spi: 0x33785672(863524466)
        transform: esp-3des esp-md5-hmac ,
        in use settings ={Tunnel, }
        conn id: 2001, flow_id: SW:1, crypto map: pix
        sa timing: remaining key lifetime (k/sec): (4431817/3286)
        IV size: 8 bytes
        replay detection support: Y
        Status: ACTIVE

     outbound ah sas:

     outbound pcp sas:

Troubleshoot

This section provides information you can use to troubleshoot your configuration.