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How to configure Dynamic-VPN with the SRX Responder behind a NAT Device

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Article ID: KB23191 KB Last Updated: 26 Feb 2020Version: 4.0
Summary:
This article provides information on how to configure Junos Pulse to connect via Dynamic VPN to an SRX device, which is behind a Static 1-to-1 NAT device.
Symptoms:
  •  Junos Pulse is connecting to SRX via Dynamic VPN.

  • SRX is the responder, which sits behind a device, is performing 1-to-1 Static NAT.


Topology:
 
JUNOS Pulse ----- Internet ------ Static NAT Device ---- SRX Device
                                  1 to 1 NAT
 
Solution:
 Dynamic VPN to an SRX device, which is behind a router/switch device and performing 1 to 1 Static NAT, will fail IPSec negotiations with Junos below 11.4R1.

Beginning with Junos 11.4R1, Dynamic-VPN to an SRX device behind a Static NAT device is supported. This requires a local-id configuration on the SRX IKE responder.

Topology:
 
JUNOS Pulse ----- Internet ------ Static NAT Device ----------- SRX Device
                                   1 to 1 NAT

172.22.145.34                                     172.22.145.33                                         172.16.10.2

In this example, the SRX device has the external-interface as 172.16.10.2. On the static NAT device, it is NAT'ing 172.16.10.2 as the 172.22.145.33 IP address.  The required IKE configuration is:

 
root@SRX220# show security ike 
policy ike-dyn-vpn-policy {
    mode aggressive;
    proposal-set compatible;
    pre-shared-key ascii-text "$ABC123"; ## SECRET-DATA
}
gateway dyn-vpn-local-gw {
    ike-policy ike-dyn-vpn-policy;
    dynamic {
        hostname dynvpn;
        connections-limit 10;
        ike-user-type group-ike-id;
    }
    local-identity inet 172.22.145.33;
    external-interface ge-0/0/0.0;
    xauth access-profile dyn-vpn-access-profile;
}
Notice that the local-identity is specified as the external public IP address, which the external-interface is advertised as out to the Pulse client. The pulse client will point its connection to the 172.22.145.33 NAT'd IP address.

Note: This procedure is different than the one listed in the documentation. It refers to a site-to-site VPN configuration, in which the SRX responder is behind a 1-to-1 static NAT device.
Modification History:
2020-02-26: minor non-technical edits.
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