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Manual Chapter: Setting Up IPsec To Use NAT Traversal on One Side of the WAN
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Overview: Setting up IPsec to use NAT traversal on one side of the WAN

When you are using IPsec to secure WAN traffic, you can set up an IPsec tunnel with NAT traversal (NAT-T) to get around a firewall or other NAT device. This implementation describes how to set up the IPsec tunnel when you have a NAT device on one side of the tunnel.

The following illustration shows a network configuration with a firewall on one side of the WAN.

Example of an IPsec deployment with NAT-T on one side of the WAN Example of an IPsec deployment with NAT-T on one side of the WAN

Before you begin IPsec configuration

Before you configure IPsec on a BIG-IP device, make sure that you have completed the following general prerequisites.

  • You must have an existing routed IP network between the two locations where the BIG-IP devices will be installed.
  • The BIG-IP hardware is installed with an initial network configuration applied. The two BIG-IP devices must be running on one of the following platforms: 1600, 3600, 3900, 6900, 8900, 8950 or 11000, VIPRION 4400/2400, or BIG-IP Virtual Edition (VE).
  • The management IP address is configured on the BIG-IP system.
  • If you are using NAT traversal, forward UDP ports 500 and 4500 to the BIG-IP system behind each firewall.
  • Verify the connectivity between the client or server and its BIG-IP device, and between each BIG-IP device and its gateway. You can use ping to test connectivity.

Task summary

When you are configuring an IPsec tunnel, you must repeat the configuration tasks on the BIG-IP systems on both sides of the WAN.

Creating a forwarding virtual server for IPsec

For IPsec, you create a forwarding virtual server to intercept IP traffic and direct it over the tunnel.
  1. On the Main tab, click Local Traffic > Virtual Servers. The Virtual Server List screen displays a list of existing virtual servers.
  2. Click the Create button. The New Virtual Server screen opens.
  3. In the Name field, type a unique name for the virtual server.
  4. From the Type list, select Forwarding (IP).
  5. For the Destination setting:
    1. For Type, select Network.
    2. In the Address field, type the IP address 0.0.0.0.
    3. In the Mask field, type the netmask 0.0.0.0.
  6. From the Service Port list, select *All Ports.
  7. From the Protocol list, select *All Protocols.
  8. From the VLAN and Tunnel Traffic list, retain the default selection, All VLANs and Tunnels.
  9. Click Finished.

Creating an IPsec tunnel with NAT-T on both sides

You can create an IPsec tunnel to securely transport application traffic across the WAN. You must configure the IPsec tunnel on the BIG-IP systems on both sides of the WAN.

When you create an IKE peer for NAT traversal (NAT-T), the key configuration detail is that the Remote Address setting is the public IP address of the firewall or other NAT device (not the IP address of the remote BIG-IP system). Also, you must turn on NAT traversal. You can customize the remaining settings to conform to your network.

ImportantColonSymbol For the IKE peer negotiations to be successful, the IKE Phase 1 and IKE Phase 2 settings must be the same on the BIG-IP systems at both ends of the IPsec tunnel.
  1. Create an IKE peer that specifies the other end of the IPsec tunnel.
    1. On the Main tab, click Network > IPsec > IKE Peers.
    2. Click the Create button.
    3. In the Name field, type a unique name for the IKE peer.
    4. In the Remote Address field, type the public IP address of the firewall or other NAT device that is between the WAN and the remote BIG-IP system. This address is the IP address of the remote peer, and must match the value of the Tunnel Remote Address setting in the relevant IPsec policy. For example, the peer remote addresses for the BIG-IP systems in Site A and Site B are as follows.
      Location Remote (Peer) Address
      Site A 165.160.15.20
      Site B 203.0.113.2
      This screen snippet shows the peer Remote Address setting at Site A. Screen showing Site A Remote Address setting
    5. For the IKE Phase 1 Algorithms area, retain the default values, or select the options that are appropriate for your deployment.
    6. In the IKE Phase 1 Credentials area, for the Authentication Method setting, select either Preshared Key or RSA Signature, and specify additional information in the fields that appear. For example, if you select Preshared Key, type the key in the Preshared Key field that becomes available. IKE Phase 1 Preshared Key setting example
      NoteColonSymbol The key you type must be the same at both ends of the tunnel.
    7. From the NAT Traversal list, select On. NAT Traversal setting example
    8. Click Finished.
  2. Create a custom IPsec policy that uses Tunnel mode and has the same remote IP address as the IKE peer.
    1. On the Main tab, click Network > IPsec > IPsec Policies.
    2. Click the Create button.
    3. In the Name field, type a unique name for the policy.
    4. For the IPsec Protocol setting, retain the default selection, ESP.
    5. From the Mode list, select Tunnel. The screen refreshes to show additional related settings.
    6. In the Tunnel Local Address field, type the local IP address of the system you are configuring. For example, the tunnel local addresses for the BIG-IP systems in Site A and Site B are as follows.
      Location Tunnel Local Address
      Site A 10.100.20.3
      Site B 10.102.20.5
    7. In the Tunnel Remote Address field, type the public IP address of the firewall or other NAT device that is between the WAN and the remote BIG-IP system. This address must match the value of the Remote Address setting for the relevant IKE peer. For example, the tunnel remote addresses for the BIG-IP systems in Site A and Site B are as follows.
      Location Tunnel Remote Address
      Site A 165.160.15.20
      Site B 203.0.113.2
      This screen snippet shows the tunnel settings at Site A.
      Example of tunnel settings at Site A
    8. For the Authentication Algorithm setting, retain the default value, or select the algorithm appropriate for your deployment.
    9. For the Encryption Algorithm setting, retain the default value, or select the algorithm appropriate for your deployment.
    10. For the Perfect Forward Secrecy setting, retain the default value, or select the option appropriate for your deployment.
    11. Click Finished.
  3. Create a bidirectional traffic selector that uses the custom IPsec policy you created. The traffic selector filters the application traffic based on the source and destination IP addresses you specify.
    1. On the Main tab, click Network > IPsec > Traffic Selectors.
    2. Click Create.
    3. In the Name field, type a unique name for the traffic selector.
    4. For the Order setting, retain the default value (First).
    5. For the Source IP Address setting, in the Address field, type the IP address from which the application traffic originates. For example, the source IP addresses for the BIG-IP systems in Site A and Site B are as follows.
      Location Source IP Address
      Site A 10.100.20.50
      Site B 10.102.20.10
    6. In the Destination IP Address setting Address field, type the final IP address for which the application traffic is destined. For example, the source IP addresses for the BIG-IP systems in Site A and Site B are as follows.
      Location Destination IP Address
      Site A 10.102.20.10
      Site B 10.100.20.50
    7. For the Action setting, retain the default value, Protect.
    8. From the IPsec Policy Name list, select the name of the custom IPsec policy that you just created. This portion of a screen is an example of the completed Traffic Selector screen at Site A. Example of completed Traffic Selector screen
    9. Click Finished.
You have now created an IPsec tunnel through which traffic travels in both directions across the WAN through firewalls on both sides.

Verifying IPsec connectivity for Tunnel mode

After you have configured an IPsec tunnel and before you configure additional functionality, you can verify that the tunnel is passing traffic.

NoteColonSymbol Only data traffic matching the traffic selector triggers the establishment of the tunnel.
.
  1. Access the tmsh command-line utility.
  2. Before sending traffic, type this command at the prompt. tmsh modify ipsec ike-daemon log-level info This command increases the logging level to display the INFO messages that you want to view.
  3. Send data traffic to the destination IP address specified in the traffic selector.
  4. Check the IKE Phase 1 negotiation status by typing this command at the prompt. racoonctl -l show-sa isakmp This example shows a result of the command. Destination is the tunnel remote IP address. Destination Cookies ST S V E Created Phase2 165.160.15.20.500 98993e6 . . . 22c87f1 9 I 10 M 2012-06-27 16:51:19 1

    This table shows the legend for interpreting the result.

    Column Displayed Description
    ST (Tunnel Status) 1 Start Phase 1 negotiation
    2 msg 1 received
    3 msg 1 sent
    4 msg 2 received
    5 msg 2 sent
    6 msg 3 received
    7 msg 3 sent
    8 msg 4 received
    9 isakmp tunnel established
    10 isakmp tunnel expired
    S I Initiator
    R Responder
    V (Version Number) 10 ISAKMP version 1.0
    E (Exchange Mode) M Main (Identity Protection)
    A Aggressive
    Phase2 <n> Number of Phase 2 tunnels negotiated with this IKE peer
  5. Check the IKE Phase 2 negotiation status by typing this command at the prompt. racoonctl -l1 show-sa internal This example shows a result of this command. Source is the tunnel local IP address. Destination is the tunnel remote IP address. Source Destination Status Side 10.100.20.3 165.160.15.20 sa established [R]

    This table shows the legend for interpreting the result.

    Column Displayed
    Side I (Initiator)
    R (Responder)
    Status init
    start
    acquire
    getspi sent
    getspi done
    1st msg sent
    1st msg recvd
    commit bit
    sa added
    sa established
    sa expired
  6. To verify the establishment of dynamic negotiated Security Associations (SAs), type this command at the prompt. racoonctl -l show-sa ipsec For each tunnel, the output displays IP addresses and information for two IPsec SAs, one for each direction, as shown in the example. 10.100.20.3 165.160.15.20 esp mode=tunnel spi=2068022822(0x7b438626) reqid=26781(0x0000689d) E: null A: hmac-sha1 9669c37c 4c83c096 beeddbde ef74d61a 2acf37ef seq=0x00000000 replay=4 flags=0x00000000 state=mature created: Dec 31 16:18:01 1969 current: Jun 29 16:40:16 2012 diff: 1341012135(s) hard: 864000(s) soft: 864000(s) last: hard: 0(s) soft: 0(s) current: 0(bytes) hard: 0(bytes) soft: 0(bytes) allocated: 0 hard: 0 soft: 0 sadb_seq=1 pid=21100 refcnt=512 165.160.15.20 10.100.20.3 esp mode=tunnel spi=1582473691(0x5e52a1db) reqid=26780(0x0000689c) E: null A: hmac-sha1 8a1b7f19 3085a5ca d0190805 18125e19 e6bda3d1 seq=0x00000000 replay=4 flags=0x00000000 state=mature created: Dec 31 16:18:01 1969 current: Jun 29 16:40:16 2012 diff: 1341012135(s) hard: 864000(s) soft: 864000(s) last: hard: 0(s) soft: 0(s) current: 0(bytes) hard: 0(bytes) soft: 0(bytes) allocated: 0 hard: 0 soft: 0 sadb_seq=0 pid=21100 refcnt=512
  7. Check the IPsec stats by typing this command at the prompt. tmsh show net ipsec-stat If traffic is passing through the IPsec tunnel, the stats will increment. ------------------------------------------------------------------- Net::Ipsec Cmd Id Mode Packets In Bytes In Packets Out Bytes Out ------------------------------------------------------------------- 0 TRANSPORT 0 0 0 0 0 TRANSPORT 0 0 0 0 0 TUNNEL 0 0 0 0 0 TUNNEL 0 0 0 0 1 TUNNEL 353.9K 252.4M 24.9K 1.8M 2 TUNNEL 117.9K 41.0M 163.3K 12.4M
  8. If the SAs are established, but traffic is not passing, type these commands at the prompt. racoonctl flush-sa isakmp racoonctl flush-sa ipsec This action forces the system to flush the existing SAs. Sending new traffic triggers SA negotiation and establishment.
  9. View the /var/log/racoon.log to verify that the IPsec tunnel is up. These lines are examples of the messages you are looking for. 2012-06-29 16:45:13: INFO: ISAKMP-SA established 10.100.20.3[500]-165.160.15.20[500] spi:3840191bd045fa51:673828cf6adc5c61 2012-06-29 16:45:14: INFO: initiate new phase 2 negotiation: 10.100.20.3[500]<=>165.160.15.20[500] 2012-06-29 16:45:14: INFO: IPsec-SA established: ESP/Tunnel 165.160.15.20[0]->10.100.20.3[0] spi=2403416622(0x8f413a2e) 2012-06-29 16:45:14: INFO: IPsec-SA established: ESP/Tunnel 10.100.20.3[0]->165.160.15.20[0] spi=4573766(0x45ca46
  10. For protocol-level troubleshooting, you can increase the debug level by typing this command at the prompt. tmsh modify net ipsec ike-daemon ikedaemon log-level debug2
    ImportantColonSymbol Use this command only for debugging. It creates a large log file, and can slow the tunnel negotiation.
    NoteColonSymbol Using this command flushes existing SAs.
  11. After you view the results, return the debug level to normal to avoid excessive logging by typing this command at the prompt. tmsh modify ipsec ike-daemon ikedaemon log-level info
    NoteColonSymbol Using this command flushes existing SAs.
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