Cisco ASA IPsec Site-to-Site VPN IKEv1 – How to Tutorial

Cisco / By /

In this tutorial I will explain the basic knowledge to understand IPsec VPN and this knowledge will be demonstrated on real use-case in the Testlab environment. I will configure two Cisco ASA Firewalls to demonstrate establishing IPsec connection using IKEv1 between these endpoints as well as packet capture for establishing  the IPsec VPN connection.

for IKEv2 version take a look at article:

Cisco ASA IPsec Site-to-Site VPN IKEv2 – How to Tutorial

Table of Contents:

1. Intro

2. Prerequisites

3. Lab setup

4. Cisco ASA1 configuration

5. Cisco ASA2 configuration

6. IPsec Tunnel bring up

7. Verify IPsec tunnel status

8. Tunnel initiation – Packet Capture

9. Conclusion

1.  Intro

Internet Protocol Security (IPsec) is a secure network protocol suite that authenticates and encrypts packets of data to provide secure encrypted communication between two computers over an Internet Protocol network. It is used in virtual private networks (VPNs).

 

When two computers establish a VPN connection, they must agree on a set of security protocols and encryption algorithms and exchange cryptographic keys to unlock and view the encrypted data. This is where IPsec enters the picture. IPsec works with VPN tunnels to establish a private bidirectional connection between devices. IPsec is not a single protocol, rather it is a complete set of protocols and standards that work together to help ensure the confidentiality, integrity, and authentication of Internet data packets flowing through a VPN tunnel. Here’s how IPsec creates a secure VPN tunnel:

  • It authenticates data to ensure the integrity of the data packet in transit
  • Encrypts Internet traffic through VPN tunnels so that the data cannot be viewed
  • Protects against data replay attacks that can lead to unauthorized logins
  • Enables secure exchange of cryptographic keys between computers
  • Offers two security modes: tunnel and transport

IPsec VPN protects the flow of data from host to host, network to network, host to network, and gateway to gateway (called tunnel mode when the entire IP packet is encrypted and authenticated).

 

IPsec protocols and components

The IPsec standard is divided into several basic protocols and supporting components.

 
Basic IPsec protocols:

Authentication Header (AH): This protocol protects the IP addresses of computers involved in a data exchange to ensure that bits of data are not lost, changed, or corrupted during transmission. AH also verifies that the person who sent the data actually sent it, protecting the tunnel from infiltration by unauthorized users.

 

Encapsulating Security Payload (ESP): The ESP protocol provides the encryption portion of IPsec, which ensures the confidentiality of data traffic between devices. ESP encrypts data packets/payloads and authenticates the payload and its origin in the IPsec protocol suite. This protocol effectively encrypts Internet traffic so that no one looking at the tunnel can see what is there.

 

Internet Key Exchange (IKE): For encryption to work, the computers involved in the exchange of private communications must share encryption keys. IKE allows two computers to securely exchange and share cryptographic keys when establishing a VPN connection. IKE establishes the SA between the communicating hosts, negotiating the cryptographic keys and algorithms that will be used in the course of the session.

There are two versions of IKE:

    • IKEv1
    • IKEv2

IKEv1 was introduced around 1998 and superseded by IKEv2 in 2005. There are some differences between the two versions:

  • IKEv2 requires less bandwidth than IKEv1.
  • IKEv2 supports EAP authentication (next to pre-shared keys and digital certificates).
  • IKEv2 has built-in support for NAT traversal (required when your IPsec peer is behind a NAT router).
  • IKEv2 has a built-in keepalive mechanism for tunnels.

IKE uses two phases:

  • IKE Phase 1
  • IKE Phase 2

ESP encrypts and authenticates data, while AH only authenticates data.

 

IPsec components:

Security Associations (SA): defines some factors of communication peers like the protocols, operational modes, encryption algorithms (DES, 3DES, AES-128, AES-192 and AES-256), shared keys of data protection in particular flows and the life cycle of SA, etc. SA is used to process data flow in one direction. Therefore, in a bi-directional communication between two peers, you need at least two security associations to protect the data flow in both of the directions.

 

Replay protection: IPSec also includes standards that prevent replay of any data packets that are part of a successful login process. This standard prevents hackers from using the replayed information to replicate the login themselves.

 

Encryption and hashing algorithms: the cryptographic key works by using a hash value that is generated by a hashing algorithm. AH and ESP are general in that they do not specify a particular type of encryption. Encryption algorithms protect the data so it cannot be read by a third-party while in transit. Authentication algorithms verify the data integrity and authenticity of a message.

 

IPsec encryption algorithms:

  • AES (Advanced Encryption Standard) — AES is the strongest encryption algorithm available. IPsec devices can use AES encryption keys of these lengths 128, 192, or 256 bits. AES is faster than 3DES.
  • 3DES (Triple-DES) — An encryption algorithm based on DES that uses the DES cipher algorithm three times to encrypt the data. The encryption key is 168-bit. 3DES is slower than AES.
  • DES (Data Encryption Standard) — Uses an encryption key that is 56 bits long. DES is the weakest of the three algorithms, and it is considered to be insecure.

IPsec authentication algorithms:

  • MD5 (Message Digest Algorithm 5) – MD5 produces a 128-bit (16 byte) message digest, which makes it faster than SHA1 or SHA2. This is the least secure algorithm.
  • SHA1 (Secure Hash Algorithm 1) – SHA1 produces a 160-bit (20 byte) message digest. Although slower than MD5, this larger digest size makes it stronger against brute force attacks. SHA-1 is considered to be mostly insecure because of a vulnerability.
  • SHA2 (Secure Hash Algorithm 2) – SHA2 is the most secure algorithm. There are three variants of SHA2 with different message digest lengths:
    • SHA2-256 — produces a 265-bit (32 byte) message digest
    • SHA2-384 — produces a 384-bit (48 byte) message digest
    • SHA2-512 — produces a 512-bit (64 byte) message digest

SHA2 is stronger than either SHA1 or MD5. We recommend that you specify a SHA2 variant.

 

Tunneling modes: tunnel and transport
IPsec sends data using tunnel or transport mode. These modes are closely related to the type of protocols used, AH or ESP.

  • Tunnel mode: In tunnel mode, the entire packet is protected. IPsec wraps the data packet in a new packet, encrypts it and adds a new IP header. It is commonly used in site-to-site VPN setups.
  • Transport mode: In transport mode, the original IP header remains and is not encrypted. Only the payload and ESP trailer are encrypted. Transport mode is often used in client-to-web VPN setups.

When it comes to VPNs, the most common IPSec configuration you will probably see is ESP with tunnel mode authentication. This structure helps Internet traffic to move securely and anonymously inside the VPN tunnel over insecure networks.

 

(For a full technical explanation of IPsec, I highly recommend the excellent article on Networklessons)

2. Prerequisites

  • Cisco ASA 9.8.1 (ASA1)
  • Cisco ASA 9.8.1 (ASA2)
  • Cisco IOS Router 15.9 (R1)
  • PC1 (some sort of Endpoint behind ASA1)
  • PC2 (some sort of Endpoint behind ASA2)

3. Lab setup

4. Cisco ASA1 configuration

a) Interface configuration:

!
interface GigabitEthernet0/0
nameif outside
security-level 0
ip address 192.0.2.6 255.255.255.252
!
interface GigabitEthernet0/1
nameif inside
security-level 100
ip address 10.0.0.254 255.255.255.0
!

b) routing configuration:

route outside 0.0.0.0 0.0.0.0 192.0.2.5 1

c) IPsec phase 2 configuration:

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

d) IPsec phase 1 configuration:

crypto ikev1 policy 1
authentication pre-share
encryption aes-256
hash sha
group 2
lifetime 86400

e) enable crypto configuration on the outside interface:

crypto ikev1 enable outside

f) configure remote endpoint for the tunnel and pre-shared key:

tunnel-group 172.16.0.2 type ipsec-l2l
tunnel-group 172.16.0.2 ipsec-attributes
ikev1 pre-shared-key MY_KEY

g) define access lists for IPsec tunnel:

access-list OUTSIDE_CRYPTOMAP_10 remark ACL to encrypt traffic from Local to Remote
access-list OUTSIDE_CRYPTOMAP_10 extended permit ip 10.0.0.0 255.255.255.0 10.1.0.0 255.255.255.0
access-list OUTSIDE_CRYPTOMAP_10 extended permit icmp 10.0.0.0 255.255.255.0 10.1.0.0 255.255.255.0

h) configure access lists, allowed through this IPsec tunnel, remote peer ip, phase 2  proposal, phase 2 SA lifetime and outgoing interface:

crypto map outside_map 10 match address OUTSIDE_CRYPTOMAP_10
crypto map outside_map 10 set peer 172.16.0.2
crypto map outside_map 10 set ikev1 transform-set MY_PROPOSAL
crypto map outside_map 10 set security-association lifetime seconds 3600
crypto map outside_map interface outside

5. Cisco ASA2 configuration

a) Interface configuration:

!
interface GigabitEthernet0/0
nameif outside
security-level 0
ip address 172.16.0.2 255.255.255.252
!
interface GigabitEthernet0/1
nameif inside
security-level 100
ip address 10.1.0.254 255.255.255.0
!

b) routing configuration:

route outside 0.0.0.0 0.0.0.0 172.16.0.1 1

c) IPsec phase 2 configuration:

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

d) IPsec phase 1 configuration:

crypto ikev1 policy 1
authentication pre-share
encryption aes-256
hash sha
group 2
lifetime 86400

e) enable crypto configuration on the outside interface:

crypto ikev1 enable outside

f) configure remote endpoint for the tunnel and pre-shared key:

tunnel-group 192.0.2.6 type ipsec-l2l
tunnel-group 192.0.2.6 ipsec-attributes
ikev1 pre-shared-key MY_KEY

g) define access lists for IPsec tunnel:

 

Note: compared to ASA1 configuration where I defined networks directly in the access-lists, in ASA2 configuration I defined network objects for remote site and local site. Those objects are configured in cryptomap which allows in the future to simply add/delete networks from the IPsec tunnel definition.

object-group network clients
network-object 10.1.0.0 255.255.255.0
object-group network vpn-remote-site
network-object 10.0.0.0 255.255.255.0
access-list OUTSIDE_CRYPTOMAP_10 remark ACL to encrypt traffic from Local to Remote
access-list OUTSIDE_CRYPTOMAP_10 extended permit ip object-group clients object-group vpn-remote-site
access-list OUTSIDE_CRYPTOMAP_10 extended permit icmp object-group clients object-group vpn-remote-site

h) configure access lists, allowed through this IPsec tunnel, remote peer ip, phase 2  proposal and outgoing interface:

crypto map outside_map 10 match address OUTSIDE_CRYPTOMAP_10
crypto map outside_map 10 set peer 192.0.2.6
crypto map outside_map 10 set ikev1 transform-set MY_PROPOSAL
crypto map outside_map 10 set security-association lifetime seconds 3600
crypto map outside_map interface outside

Full ASA1, ASA2, R1 configuration:

ASA1# sh run
: Saved

:
: Serial Number: 9A3TUHU3UHM
: Hardware: ASAv, 2048 MB RAM, CPU Pentium II 2808 MHz
:
ASA Version 9.8(1)
!
hostname ASA1
enable password $sha512$5000$PmQWx2sWe2gpAR7hTexRGw==$YD8dkeI/EJWmyJO7hwO4Wg== pbkdf2
xlate per-session deny tcp any4 any4
xlate per-session deny tcp any4 any6
xlate per-session deny tcp any6 any4
xlate per-session deny tcp any6 any6
xlate per-session deny udp any4 any4 eq domain
xlate per-session deny udp any4 any6 eq domain
xlate per-session deny udp any6 any4 eq domain
xlate per-session deny udp any6 any6 eq domain
names

!
interface GigabitEthernet0/0
 nameif outside
 security-level 0
 ip address 192.0.2.6 255.255.255.252
!
interface GigabitEthernet0/1
 nameif inside
 security-level 100
 ip address 10.0.0.254 255.255.255.0
!
interface GigabitEthernet0/2
 shutdown
 no nameif
 no security-level
 no ip address
!
interface GigabitEthernet0/3
 shutdown
 no nameif
 no security-level
 no ip address
!
interface GigabitEthernet0/4
 shutdown
 no nameif
 no security-level
 no ip address
!
interface GigabitEthernet0/5
 shutdown
 no nameif
 no security-level
 no ip address
!
interface GigabitEthernet0/6
 shutdown
 no nameif
 no security-level
 no ip address
!
interface Management0/0
 shutdown
 no nameif
 no security-level
 no ip address
!
ftp mode passive
access-list OUTSIDE_CRYPTOMAP_10 remark ACL to encrypt traffic from Local to Remote
access-list OUTSIDE_CRYPTOMAP_10 extended permit ip 10.0.0.0 255.255.255.0 10.1.0.0 255.255.255.0
access-list OUTSIDE_CRYPTOMAP_10 extended permit icmp 10.0.0.0 255.255.255.0 10.1.0.0 255.255.255.0
pager lines 23
logging console debugging
mtu outside 1500
mtu inside 1500
no failover
no monitor-interface service-module
icmp unreachable rate-limit 1 burst-size 1
no asdm history enable
arp timeout 14400
no arp permit-nonconnected
arp rate-limit 8192
route outside 0.0.0.0 0.0.0.0 192.0.2.5 1
timeout xlate 3:00:00
timeout pat-xlate 0:00:30
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 sctp 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 sip-provisional-media 0:02:00 uauth 0:05:00 absolute
timeout tcp-proxy-reassembly 0:01:00
timeout floating-conn 0:00:00
timeout conn-holddown 0:00:15
timeout igp stale-route 0:01:10
user-identity default-domain LOCAL
aaa authentication ssh console LOCAL
aaa authentication login-history
no snmp-server location
no snmp-server contact
crypto ipsec ikev1 transform-set MY_PROPOSAL esp-aes-256 esp-sha-hmac
crypto ipsec security-association pmtu-aging infinite
crypto map outside_map 10 match address OUTSIDE_CRYPTOMAP_10
crypto map outside_map 10 set peer 172.16.0.2
crypto map outside_map 10 set ikev1 transform-set MY_PROPOSAL
crypto map outside_map 10 set security-association lifetime seconds 3600
crypto map outside_map interface outside
crypto ca trustpoint _SmartCallHome_ServerCA
 no validation-usage
crl configure
crypto ca trustpool policy
 auto-import
crypto ca certificate chain _SmartCallHome_ServerCA
certificate ca 18dad19e267de8bb4a2158cdcc6b3b4a
308204d3 308203bb a0030201 02021018 dad19e26 7de8bb4a 2158cdcc 6b3b4a30
0d06092a 864886f7 0d010105 05003081 ca310b30 09060355 04061302 55533117
30150603 55040a13 0e566572 69536967 6e2c2049 6e632e31 1f301d06 0355040b
13165665 72695369 676e2054 72757374 204e6574 776f726b 313a3038 06035504
0b133128 63292032 30303620 56657269 5369676e 2c20496e 632e202d 20466f72
20617574 686f7269 7a656420 75736520 6f6e6c79 31453043 06035504 03133c56
65726953 69676e20 436c6173 73203320 5075626c 69632050 72696d61 72792043
65727469 66696361 74696f6e 20417574 686f7269 7479202d 20473530 1e170d30
36313130 38303030 3030305a 170d3336 30373136 32333539 35395a30 81ca310b
30090603 55040613 02555331 17301506 0355040a 130e5665 72695369 676e2c20
xxxxxxxx 311f301d 06035504 0b131656 65726953 69676e20 54727573 74204e65
74776f72 6b313a30 38060355 040b1331 28632920 32303036 20566572 69536967
6e2c2049 6e632e20 2d20466f 72206175 74686f72 697a6564 20757365 206f6e6c
79314530 43060355 0403133c xxxxxxxx 5369676e 20436c61 73732033 20507562
6c696320 5072696d 61727920 43657274 69666963 6174696f 6e204175 74686f72
69747920 2d204735 30820122 300d0609 2a864886 f70d0101 01050003 82010f00
3082010a 02820101 00af2408 08297a35 9e600caa e74b3b4e dc7cbc3c 451cbb2b
e0fe2902 f95708a3 64851527 f5f1adc8 31895d22 e82aaaa6 42b38ff8 b955b7b1
b74bb3fe 8f7e0757 ecef43db 66621561 cf600da4 d8def8e0 c362083d 5413eb49
ca595485 26e52b8f 1b9febf5 a191c233 49d84363 6a524bd2 8fe87051 4dd18969
7bc770f6 b3dc1274 db7b5d4b 56d396bf 1577a1b0 f4a225f2 af1c9267 18e5f406
04ef90b9 e400e4dd 3ab519ff 02baf43c eee08beb 378becf4 d7acf2f6 f03dafdd
75913319 1d1c40cb 74241921 93d914fe ac2a52c7 8fd50449 e48d6347 883c6983
cbfe47bd 2b7e4fc5 95ae0e9d d4d143c0 6773e314 087ee53f 9f73b833 0acf5d3f
3487968a ee53e825 15020301 0001a381 b23081af 300f0603 551d1301 01ff0405
30030101 xxxxxxxx 03551d0f 0101ff04 04030201 06306d06 082b0601 05050701
0c046130 5fa15da0 5b305930 57305516 09696d61 67652f67 69663021 301f3007
06052b0e 03021a04 148fe5d3 1a86ac8d xxxxxxxx 806ad448 182c7b19 2e302516
23687474 703a2f2f 6c6f676f 2e766572 69736967 6e2e636f 6d2f7673 6c6f676f
2e676966 301d0603 551d0e04 1604147f d365a7c2 ddecbbf0 3009f343 39fa02af
33313330 0d06092a 864886f7 0d010105 05000382 01010093 244a305f 62cfd81a
982f3dea dc992dbd 77f6a579 2238ecc4 a7a07812 ad620e45 7064c5e7 97662d98
097e5faf d6cc2865 f201aa08 1a47def9 f97c925a 0869200d d93e6d6e 3c0d6ed8
e6069140 18b9f8c1 eddfdb41 aae09620 c9cd6415 3881c994 eea28429 0b136f8e
db0cdd25 02dba48b 1944d241 7a05694a 584f60ca 7e826a0b 02aa2517 39b5db7f
e784652a 958abd86 de5e8116 832d10cc defda882 2a6d281f 0d0bc4e5 e71a2619
e1f4116f 10b595fc e7420532 dbce9d51 5e28b69e 85d35bef a57d4540 728eb70e
6b0e06fb 33354871 b89d278b c4655f0d 86769c44 7af6955c f65d3208 33a454b6
183f685c f2424a85 3854835f d1e82cf2 ac11d6a8 ed636a
quit
crypto ikev1 enable outside
crypto ikev1 policy 1
 authentication pre-share
 encryption aes-256
 hash sha
 group 2
 lifetime 86400
telnet timeout 5
ssh stricthostkeycheck
ssh 0.0.0.0 0.0.0.0 outside
ssh timeout 5
ssh key-exchange group dh-group1-sha1
console timeout 0
threat-detection basic-threat
threat-detection statistics access-list
no threat-detection statistics tcp-intercept
dynamic-access-policy-record DfltAccessPolicy
username admin password $sha512$5000$Z1h0SF6xnUUaq1dvq+9Bww==$PKx2+0wiLLyuICE5Q2e1nA== pbkdf2 privilege 15
tunnel-group 172.16.0.2 type ipsec-l2l
tunnel-group 172.16.0.2 ipsec-attributes
 ikev1 pre-shared-key *****
!
class-map inspection_default
 match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
parameters
message-length maximum client auto
message-length maximum 512
no tcp-inspection
policy-map global_policy
class inspection_default
inspect ip-options
inspect netbios
inspect rtsp
inspect sunrpc
inspect tftp
inspect xdmcp
inspect dns preset_dns_map
inspect ftp
inspect h323 h225
inspect h323 ras
inspect rsh
inspect esmtp
inspect sqlnet
inspect sip
inspect skinny
policy-map type inspect dns migrated_dns_map_2
parameters
message-length maximum client auto
message-length maximum 512
no tcp-inspection
policy-map type inspect dns migrated_dns_map_1
parameters
message-length maximum client auto
message-length maximum 512
no tcp-inspection
!
service-policy global_policy global
prompt hostname context
no call-home reporting anonymous
call-home
profile CiscoTAC-1
no active
destination address http https://tools.cisco.com/its/service/oddce/services/DDCEService
destination address email callhome@cisco.com
destination transport-method http
subscribe-to-alert-group diagnostic
subscribe-to-alert-group environment
subscribe-to-alert-group inventory periodic monthly
subscribe-to-alert-group configuration periodic monthly
subscribe-to-alert-group telemetry periodic daily
profile License
destination address http https://tools.cisco.com/its/service/oddce/services/DDCEService
destination transport-method http
Cryptochecksum:b6e0730543bfee38d6e5b80504cd04f1
: end
ASA2# sh run
: Saved

:
: Serial Number: 9ARXAP319S4
: Hardware: ASAv, 2048 MB RAM, CPU Pentium II 2808 MHz
:
ASA Version 9.8(1)
!
hostname ASA2
enable password $sha512$5000$pXa6MemA32DY/sNQRr2PCQ==$CAVbxflwQpdm9lU/5Girtg== pbkdf2
xlate per-session deny tcp any4 any4
xlate per-session deny tcp any4 any6
xlate per-session deny tcp any6 any4
xlate per-session deny tcp any6 any6
xlate per-session deny udp any4 any4 eq domain
xlate per-session deny udp any4 any6 eq domain
xlate per-session deny udp any6 any4 eq domain
xlate per-session deny udp any6 any6 eq domain
names

!
interface GigabitEthernet0/0
 nameif outside
 security-level 0
 ip address 172.16.0.2 255.255.255.252
!
interface GigabitEthernet0/1
 nameif inside
 security-level 100
 ip address 10.1.0.254 255.255.255.0
!
interface GigabitEthernet0/2
 shutdown
 no nameif
 no security-level
 no ip address
!
interface GigabitEthernet0/3
 shutdown
 no nameif
 no security-level
 no ip address
!
interface GigabitEthernet0/4
 shutdown
 no nameif
 no security-level
 no ip address
!
interface GigabitEthernet0/5
 shutdown
 no nameif
 no security-level
 no ip address
!
interface GigabitEthernet0/6
 shutdown
 no nameif
 no security-level
 no ip address
!
interface Management0/0
 shutdown
 no nameif
 no security-level
 no ip address
!
ftp mode passive
object-group network clients
 network-object 10.1.0.0 255.255.255.0
object-group network vpn-remote-site
 network-object 10.0.0.0 255.255.255.0
access-list OUTSIDE_CRYPTOMAP_10 remark ACL to encrypt traffic from Local to Remote
access-list OUTSIDE_CRYPTOMAP_10 extended permit ip object-group clients object-group vpn-remote-site
access-list OUTSIDE_CRYPTOMAP_10 extended permit icmp object-group clients object-group vpn-remote-site
access-list clients-out extended permit icmp any any
access-list clients-out extended permit ip object-group clients any
pager lines 23
mtu outside 1500
mtu inside 1500
no failover
no monitor-interface service-module
icmp unreachable rate-limit 1 burst-size 1
no asdm history enable
arp timeout 14400
no arp permit-nonconnected
arp rate-limit 8192
access-group clients-out in interface inside
route outside 0.0.0.0 0.0.0.0 172.16.0.1 1
timeout xlate 3:00:00
timeout pat-xlate 0:00:30
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 sctp 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 sip-provisional-media 0:02:00 uauth 0:05:00 absolute
timeout tcp-proxy-reassembly 0:01:00
timeout floating-conn 0:00:00
timeout conn-holddown 0:00:15
timeout igp stale-route 0:01:10
user-identity default-domain LOCAL
aaa authentication ssh console LOCAL
aaa authentication login-history
no snmp-server location
no snmp-server contact
crypto ipsec ikev1 transform-set MY_PROPOSAL esp-aes-256 esp-sha-hmac
crypto ipsec security-association pmtu-aging infinite
crypto map outside_map 10 match address OUTSIDE_CRYPTOMAP_10
crypto map outside_map 10 set peer 192.0.2.6
crypto map outside_map 10 set ikev1 transform-set MY_PROPOSAL
crypto map outside_map 10 set security-association lifetime seconds 3600
crypto map outside_map interface outside
crypto ca trustpoint _SmartCallHome_ServerCA
 no validation-usage
 crl configure
crypto ca trustpool policy
 auto-import
crypto ca certificate chain _SmartCallHome_ServerCA
certificate ca 18dad19e267de8bb4a2158cdcc6b3b4a
308204d3 308203bb a0030201 02021018 dad19e26 7de8bb4a 2158cdcc 6b3b4a30
0d06092a 864886f7 0d010105 05003081 ca310b30 09060355 04061302 55533117
30150603 55040a13 0e566572 69536967 6e2c2049 6e632e31 1f301d06 0355040b
13165665 72695369 676e2054 72757374 204e6574 776f726b 313a3038 06035504
0b133128 63292032 30303620 56657269 5369676e 2c20496e 632e202d 20466f72
20617574 686f7269 7a656420 75736520 6f6e6c79 31453043 06035504 03133c56
65726953 69676e20 436c6173 73203320 5075626c 69632050 72696d61 72792043
65727469 66696361 74696f6e 20417574 686f7269 7479202d 20473530 1e170d30
36313130 38303030 3030305a 170d3336 30373136 32333539 35395a30 81ca310b
30090603 55040613 02555331 17301506 0355040a 130e5665 72695369 676e2c20
496e632e 311f301d 06035504 0b131656 65726953 69676e20 54727573 74204e65
74776f72 6b313a30 38060355 040b1331 28632920 32303036 20566572 69536967
6e2c2049 6e632e20 2d20466f 72206175 74686f72 697a6564 20757365 206f6e6c
79314530 43060355 0403133c 56657269 5369676e 20436c61 73732033 20507562
6c696320 5072696d 61727920 43657274 69666963 6174696f 6e204175 74686f72
69747920 2d204735 30820122 300d0609 2a864886 f70d0101 01050003 82010f00
xxxxxxxx 02820101 00af2408 08297a35 9e600caa e74b3b4e dc7cbc3c 451cbb2b
e0fe2902 f95708a3 64851527 f5f1adc8 31895d22 e82aaaa6 42b38ff8 b955b7b1
b74bb3fe 8f7e0757 ecef43db 66621561 cf600da4 d8def8e0 c362083d 5413eb49
ca595485 26e52b8f 1b9febf5 a191c233 49d84363 6a524bd2 8fe87051 4dd18969
7bc770f6 b3dc1274 xxxxxxxx 56d396bf 1577a1b0 f4a225f2 af1c9267 18e5f406
04ef90b9 e400e4dd 3ab519ff 02baf43c eee08beb 378becf4 d7acf2f6 f03dafdd
75913319 1d1c40cb 74241921 93d914fe ac2a52c7 8fd50449 e48d6347 883c6983
cbfe47bd 2b7e4fc5 95ae0e9d d4d143c0 6773e314 087ee53f 9f73b833 0acf5d3f
3487968a ee53e825 15020301 0001a381 b23081af 300f0603 551d1301 01ff0405
30030101 ff300e06 03551d0f 0101ff04 04030201 06306d06 082b0601 05050701
0c046130 xxxxxxxx 5b305930 57305516 09696d61 67652f67 69663021 301f3007
06052b0e 03021a04 148fe5d3 1a86ac8d 8e6bc3cf 806ad448 182c7b19 2e302516
23687474 703a2f2f 6c6f676f 2e766572 xxxxxxxx 6e2e636f 6d2f7673 6c6f676f
2e676966 301d0603 551d0e04 1604147f d365a7c2 ddecbbf0 3009f343 39fa02af
33313330 0d06092a 864886f7 0d010105 05000382 01010093 244a305f 62cfd81a
982f3dea dc992dbd 77f6a579 2238ecc4 a7a07812 ad620e45 7064c5e7 97662d98
097e5faf d6cc2865 f201aa08 1a47def9 f97c925a 0869200d d93e6d6e 3c0d6ed8
e6069140 18b9f8c1 eddfdb41 aae09620 c9cd6415 3881c994 eea28429 0b136f8e
db0cdd25 02dba48b 1944d241 7a05694a 584f60ca 7e826a0b 02aa2517 39b5db7f
e784652a 958abd86 de5e8116 832d10cc defda882 2a6d281f 0d0bc4e5 e71a2619
e1f4116f 10b595fc e7420532 dbce9d51 5e28b69e 85d35bef a57d4540 728eb70e
6b0e06fb 33354871 b89d278b c4655f0d 86769c44 7af6955c f65d3208 33a454b6
183f685c f2424a85 3854835f d1e82cf2 ac11d6a8 ed636a
quit
crypto ikev1 enable outside
crypto ikev1 policy 1
 authentication pre-share
 encryption aes-256
 hash sha
 group 2
 lifetime 86400
telnet timeout 5
ssh stricthostkeycheck
ssh 0.0.0.0 0.0.0.0 outside
ssh timeout 5
ssh key-exchange group dh-group1-sha1
console timeout 0
threat-detection basic-threat
threat-detection statistics access-list
no threat-detection statistics tcp-intercept
dynamic-access-policy-record DfltAccessPolicy
username admin password $sha512$5000$Wvcm8Eg8bclZpmeduKKJgQ==$b3sgYTJSLIzUEL+9nvwAwg== pbkdf2 privilege 15
tunnel-group 192.0.2.6 type ipsec-l2l
tunnel-group 192.0.2.6 ipsec-attributes
 ikev1 pre-shared-key *****
!
class-map inspection_default
match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
parameters
message-length maximum client auto
message-length maximum 512
no tcp-inspection
policy-map global_policy
class inspection_default
inspect ip-options
inspect netbios
inspect rtsp
inspect sunrpc
inspect tftp
inspect xdmcp
inspect dns preset_dns_map
inspect ftp
inspect h323 h225
inspect h323 ras
inspect rsh
inspect esmtp
inspect sqlnet
inspect sip
inspect skinny
policy-map type inspect dns migrated_dns_map_2
parameters
message-length maximum client auto
message-length maximum 512
no tcp-inspection
policy-map type inspect dns migrated_dns_map_1
parameters
message-length maximum client auto
message-length maximum 512
no tcp-inspection
!
service-policy global_policy global
prompt hostname context
no call-home reporting anonymous
call-home
profile CiscoTAC-1
no active
destination address http https://tools.cisco.com/its/service/oddce/services/DDCEService
destination address email callhome@cisco.com
destination transport-method http
subscribe-to-alert-group diagnostic
subscribe-to-alert-group environment
subscribe-to-alert-group inventory periodic monthly
subscribe-to-alert-group configuration periodic monthly
subscribe-to-alert-group telemetry periodic daily
profile License
destination address http https://tools.cisco.com/its/service/oddce/services/DDCEService
destination transport-method http
Cryptochecksum:89ba44901c9fa8d30f6ae9a6a8ad135d
: end
ASA2#
R1#sh run
Building configuration...

Current configuration : 3111 bytes
!
version 15.9
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R1
!
boot-start-marker
boot-end-marker
!
!
!
no aaa new-model
!
!
!
mmi polling-interval 60
no mmi auto-configure
no mmi pvc
mmi snmp-timeout 180
!
!
!
!
!
no ip icmp rate-limit unreachable
!
!
!
!
!
!
no ip domain lookup
ip cef
no ipv6 cef
!
multilink bundle-name authenticated
!
!
!
redundancy
!
no cdp log mismatch duplex
!
ip tcp synwait-time 5
!
!
!
!
interface GigabitEthernet0/0
ip address 172.16.0.1 255.255.255.252
duplex auto
speed auto
media-type rj45
!
interface GigabitEthernet0/1
ip address 192.0.2.5 255.255.255.252
duplex auto
speed auto
media-type rj45
!
interface GigabitEthernet0/2
no ip address
shutdown
duplex auto
speed auto
media-type rj45
!
interface GigabitEthernet0/3
no ip address
shutdown
duplex auto
speed auto
media-type rj45
!
ip forward-protocol nd
!
!
no ip http server
!
ipv6 ioam timestamp
!
!
!
control-plane
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
line vty 0 4
login
transport input none
!
no scheduler allocate
!
end

R1#

6. IPsec Tunnel bring up

  • To bring up IPsec tunnel it is needed to generate interesting traffic from one side (except permanent IPsec tunnels).
  • Interesting traffic is the traffic that is allowed in the encryption domain.
  • The encryption domain represents the traffic that participates in VPN Tunnel.

In our case encryption domain on ASA1 contains subnet 10.0.0.0/24 and encryption domain on ASA2 contains 10.1.0.0/24. If we want to bring up the IPsec tunnel from ASA1 side for example, it is needed to generate traffic for other side of the tunnel with destination in network 10.1.0.0/24.

a) verify that no VPN tunnel exists before we will bring the VPN tunnel up:

ASA1# show crypto ipsec sa

There are no ipsec sas
ASA1#
ASA2# sh crypto ipsec sa

There are no ipsec sas
ASA2#

b) bring up the IPsec VPN tunnel up:

 

Note: I will generate interesting traffic using icmp ping test from PC1 (10.0.0.1) to PC2 (10.1.0.1)

PC1> ping 10.1.0.1

10.1.0.1 icmp_seq=1 timeout
84 bytes from 10.1.0.1 icmp_seq=2 ttl=64 time=4.949 ms
84 bytes from 10.1.0.1 icmp_seq=3 ttl=64 time=2.930 ms
84 bytes from 10.1.0.1 icmp_seq=4 ttl=64 time=2.192 ms
84 bytes from 10.1.0.1 icmp_seq=5 ttl=64 time=3.235 ms

PC1>

IPsec Tunnel is up and functional.

7. Verify IPsec tunnel status

There are following major ways to check IPsec tunnel status:

  • show crypto ipsec sa (Show IPsec SAs for Phase 1)
  • show crypto ikev1 sa (Show IKEv1 sas for Phase 2)

Let’s verify IPsec tunnel status on ASA1 and ASA2 and take a look on IPsec SA parameter and IKEv1 parameter.

ASA1# show crypto ipsec sa
interface: outside
Crypto map tag: outside_map, seq num: 10, local addr: 192.0.2.6

access-list OUTSIDE_CRYPTOMAP_10 extended permit ip 10.0.0.0 255.255.255.0 10.1.0.0 255.255.255.0
local ident (addr/mask/prot/port): (10.0.0.0/255.255.255.0/0/0)
remote ident (addr/mask/prot/port): (10.1.0.0/255.255.255.0/0/0)
current_peer: 172.16.0.2


#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
#TFC rcvd: 0, #TFC sent: 0
#Valid ICMP Errors rcvd: 0, #Invalid ICMP Errors rcvd: 0
#send errors: 0, #recv errors: 0

local crypto endpt.: 192.0.2.6/0, remote crypto endpt.: 172.16.0.2/0
path mtu 1500, ipsec overhead 74(44), media mtu 1500
PMTU time remaining (sec): 0, DF policy: copy-df
ICMP error validation: disabled, TFC packets: disabled
current outbound spi: 4A4E6F7B
current inbound spi : 6DC52AD9

inbound esp sas:
spi: 0x6DC52AD9 (1841638105)
SA State: active
transform: esp-aes-256 esp-sha-hmac no compression
in use settings ={L2L, Tunnel, IKEv1, }
slot: 0, conn_id: 124293120, crypto-map: outside_map
sa timing: remaining key lifetime (kB/sec): (4373999/3588)
IV size: 16 bytes
replay detection support: Y
Anti replay bitmap:
0x00000000 0x0000001F
outbound esp sas:
spi: 0x4A4E6F7B (1246654331)
SA State: active
transform: esp-aes-256 esp-sha-hmac no compression
in use settings ={L2L, Tunnel, IKEv1, }
slot: 0, conn_id: 124293120, crypto-map: outside_map
sa timing: remaining key lifetime (kB/sec): (4373999/3588)
IV size: 16 bytes
replay detection support: Y
Anti replay bitmap:
0x00000000 0x00000001

ASA1# show crypto ikev1 sa

IKEv1 SAs:

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: 172.16.0.2
Type : L2L Role : initiator
Rekey : no State : MM_ACTIVE
ASA1#
ASA2# show crypto ikev1 sa

There are no IKEv1 SAs
ASA2# show crypto ipsec sa
interface: outside
Crypto map tag: outside_map, seq num: 10, local addr: 172.16.0.2

access-list OUTSIDE_CRYPTOMAP_10 extended permit ip 10.1.0.0 255.255.255.0 10.0.0.0 255.255.255.0
local ident (addr/mask/prot/port): (10.1.0.0/255.255.255.0/0/0)
remote ident (addr/mask/prot/port): (10.0.0.0/255.255.255.0/0/0)
current_peer: 192.0.2.6


#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
#TFC rcvd: 0, #TFC sent: 0
#Valid ICMP Errors rcvd: 0, #Invalid ICMP Errors rcvd: 0
#send errors: 0, #recv errors: 0

local crypto endpt.: 172.16.0.2/0, remote crypto endpt.: 192.0.2.6/0
path mtu 1500, ipsec overhead 74(44), media mtu 1500
PMTU time remaining (sec): 0, DF policy: copy-df
ICMP error validation: disabled, TFC packets: disabled
current outbound spi: 6DC52AD9
current inbound spi : 4A4E6F7B

inbound esp sas:
spi: 0x4A4E6F7B (1246654331)
SA State: active
transform: esp-aes-256 esp-sha-hmac no compression
in use settings ={L2L, Tunnel, IKEv1, }
slot: 0, conn_id: 218001408, crypto-map: outside_map
sa timing: remaining key lifetime (kB/sec): (3914999/3582)
IV size: 16 bytes
replay detection support: Y
Anti replay bitmap:
0x00000000 0x0000001F
outbound esp sas:
spi: 0x6DC52AD9 (1841638105)
SA State: active
transform: esp-aes-256 esp-sha-hmac no compression
in use settings ={L2L, Tunnel, IKEv1, }
slot: 0, conn_id: 218001408, crypto-map: outside_map
sa timing: remaining key lifetime (kB/sec): (3914999/3582)
IV size: 16 bytes
replay detection support: Y
Anti replay bitmap:
0x00000000 0x00000001

ASA2# show crypto ikev1 sa

IKEv1 SAs:

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: 192.0.2.6
Type : L2L Role : responder
Rekey : no State : MM_ACTIVE
ASA2#
Knowledge base
  1. interface: outside
    1. interface on which the tunnel is established
  2. Crypto map tag: outside_map, seq num: 10, local addr: 192.0.2.6
    1. crypto map for this tunnel
    2. ip address of local endpoint
  3. access-list OUTSIDE_CRYPTOMAP_10 extended permit ip 10.0.0.0 255.255.255.0 10.1.0.0 255.255.255.0
    1. access list allowed to communicate through the tunnel
  4. local ident (addr/mask/prot/port): (10.0.0.0/255.255.255.0/0/0)
    remote ident (addr/mask/prot/port): (10.1.0.0/255.255.255.0/0/0)
    current_peer: 172.16.0.2
    1. local encryption domain
    2. remote encryption domain
    3. remote peer ip
  5. #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
    #TFC rcvd: 0, #TFC sent: 0
    #Valid ICMP Errors rcvd: 0, #Invalid ICMP Errors rcvd: 0
    #send errors: 0, #recv errors: 0
    1. tunnel statistics, encrypted packets, decrypted packets etc.
  6. local crypto endpt.: 192.0.2.6/0, remote crypto endpt.: 172.16.0.2/0
    1. local peer ip and source port, remote peer ip and destination port, in case of ESP Protocol 0 is shown in stats
  7. current outbound spi: 4A4E6F7B
    current inbound spi : 6DC52AD9
    1. spi for outbound and inbound tunnel. (The Security Parameter Index (SPI) is an identification tag added to the header while using IPsec for tunneling the IP traffic.)
  8. inbound esp sas:
       spi: 0x6DC52AD9 (1841638105)
          SA State: active
          transform: esp-aes-256 esp-sha-hmac no compression
          in use settings ={L2L, Tunnel, IKEv1, }
          slot: 0, conn_id: 124293120, crypto-map: outside_map
          sa timing: remaining key lifetime (kB/sec): (4373999/3588)
          IV size: 16 bytes
          replay detection support: Y
          Anti replay bitmap:
           0x00000000 0x0000001F
    outbound esp sas:
       spi: 0x4A4E6F7B (1246654331)
          SA State: active
          transform: esp-aes-256 esp-sha-hmac no compression
          in use settings ={L2L, Tunnel, IKEv1, }
          slot: 0, conn_id: 124293120, crypto-map: outside_map
          sa timing: remaining key lifetime (kB/sec): (4373999/3588)
          IV size: 16 bytes
          replay detection support: Y
          Anti replay bitmap:
          0x00000000 0x00000001
    1. detailed parameter of the SPIs, SA State for the spi, lifetime, etc

  9. IKEv1 SAs:

    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: 172.16.0.2
    Type : L2L Role : initiator
    Rekey : no State : MM_ACTIVE

    1. IKE version 1 parameter:
      1. Status, active SA’s Count
      2. Rekeys / rekey SA’s Count
      3. IKE peer IP
      4. Node is either Initiator or Responder
      5. Main Mode (MM) or Aggressive Mode (AM)

Commands for debugging and troubleshoot VPN tunnel problems:

The ASA debugs for tunnel negotiation are:

  • debug crypto ikev1 <1-255>

The ASA debug for certificate authentication is:

  • debug crypto ca

VPN Tunnel reset:

  • clear crypto ipsec sa peer <remote-peer-IP>

Learn more on Cisco TechNotes:

Configure IKEv1 IPsec Site-to-Site Tunnels with the ASDM or CLI on the ASA

Configure Site-to-Site IKEv2 Tunnel between ASA and Router

8. Tunnel initiation – Packet Capture

In this section we will take a deeper look how the IPsec IKEv1 Site-to-Site VPN Tunnel initiation looks like on the packet level. I will make packet capture on ASA1 and ASA2 outside interfaces at the same time and then interesting traffic will be generated to bring up the tunnel.

Knowledge base
  1. IKEv1 Main Mode negotiation uses six ISAKMP packets for the initial phase-1 exchange (packets 1-6)
  2. IKE SA establishment and key generation for phase-2 quick mode (packets 7-9)
  3. ESP packets n.10 – n.17 are our icmp encrypted traffic – the SPIs from source to destination and from destination to source are matching the SPIs in the ASA “show crypto ipsec details” details.
  4. first packet (packet n.6) is carrying initial information such as: Encryption Algorithm, Integrity Algorithm, Diffie-Hellman group. This comes from the initiation ASA1 IPsec configuration. For the successful initiation of the IPsec Tunnel there should be a match between initiator proposal (in our case ASA1) and the responder proposal (in our case ASA2)

Let’s take a deeper look into the Payload:

The packet captures on both sides should be identical:

9. Conclusion

In this how to/tutorial I explained the basic theory to understand IPsec, how to configure Cisco ASA IPsec Tunnel with IKEv1, how to read and debug the IPsec parameter with help of tcpdump packet capture during tunnel initiation.