EdgeRouter - Site-to-Site IPsec VPN to USG


Readers will learn how to configure a Policy-Based Site-to-Site IPsec VPN between an EdgeRouter and an UniFi Security Gateway (USG).

A Policy-Based VPN is characterized by the definition of local and remote subnets (proxy IDs). This type of VPN differs from a Route-Based VPN which is characterized by the usage of Virtual Tunnel Interfaces (VTIs) and routing entries.

book_25x25.png    NOTES & REQUIREMENTS:

Applicable to EdgeOS 1.9.7 + firmware in all EdgeRouter models. Knowledge of the Command Line Interface (CLI), UniFi Controller, and basic networking knowledge is required. Please see the Related Articles below for more information and see the attachments for the configurations used in this article.


Equipment used in this article:

- EdgeRouter-X (ER-X)

- UniFi Security Gateway (USG)

- Test clients behind the peers (Host1 and Server1)

Table of Contents

  1. Network Diagram
  2. Steps: Policy-Based VPN
  3. Steps: USG VPN
  4. Steps: Testing & Verification
  5. Related Articles

Network Diagram

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The network topology is shown below. The following interfaces are in use on the EdgeRouter and the USG:


  1. eth0 (WAN) -
  2. eth1 (LAN) -


  1. eth0 (WAN) -
  2. eth1 (LAN) -

Steps: Policy-Based VPN

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For the purpose of this article it is assumed that the routing and interface configuration is already in place and that reachability has been tested.

The UDP ports and protocols relevant to IPsec are:

  1. UDP 500 (IKE)
  2. ESP (Protocol 50)
  3. UDP 4500 (NAT-T)

The type of VPN that will be created is called a Policy-Based VPN which uses remote and local subnets, otherwise known as proxy IDs. These values need to match exactly between the two peers and need to be mirrored images of each other. Only the prefixes defined in the proxy IDs will be carried over the tunnel. In the example ER has the present on the LAN side, whereas the UniFi side uses

The first part of the configuration focuses on the ER, afterwards the VPN will be set up on the USG.

www.png  GUI STEPS: Access the router's Web-Management Portal (GUI).

1. Define the IPsec peer and Security Associations (SAs) on the ER (replace <secret> with your desired passphrase).

VPN > IPsec Site-to-Site > +Add Peer

  • Show advanced options
  • Automatically open firewall and exclude from NAT
Description: IPsec
Local IP:
Encryption: AES-256
Hash: SHA1
DH Group: 14
Pre-shared Secret: <secret>
Local subnet:
Remote subnet: 
info_i_25x25.png Note: It is also possible to use a non-static IP address for the WAN connection. In the case of DHCP, please proceed to the CLI steps below. For PPPoE interfaces or load-balancing scenarios it is currently recommend to use over Local IP ‘any’.


CLI_circle.png  CLI STEPS (DHCP): Access the command line interface (CLI). You can do this using the CLI button in the GUI or by using a program such as PuTTY.

1. Enter configuration mode.


2. Display the current IPsec VPN peer configuration (only relevant output is shown).

show vpn
ipsec {
   site-to-site {
       peer {

3. (Optional) Remove the local IPsec peer address.

delete vpn ipsec site-to-site peer local-address

4. (Optional) Define the local IPsec DHCP peer address for the WAN interface.

set vpn ipsec site-to-site peer dhcp-interface eth0

5. (Optional) Enable the IPsec offloading feature to increase ESP (not IKE) performance.

set system offload ipsec enable (this requires a reboot to become active)

6. Commit the changes.


7. Save the configuration.


Steps: USG VPN

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Please make sure that the latest stable version of UniFi is being used and that the device is capable of reaching the internet. 

www.png  GUI STEPS: Access the UniFi Controller Web-Management (GUI). 

1. Assign a public IP address to the USG. Under the Devices section, click on the USG to expand the Properties panel. Under Configuration, click to expand the WAN section and fill out:

Connection Type: Static IP
IP address:
Preferred DNS:
Subnet Mask:

2. Modify the LAN network or leave it at the default setting (depending on your scenario). Do so under Settings > Networks > LAN > edit

Name: LAN
Purpose: Corporate
Parent Interface: LAN
DHCP Server: Enable
DHCP Range: -

3. Create a new network that will be used for IPsec (replace <secret> with your desired passphrase).

  • Show advanced options
  • Uncheck Dynamic Routing
  • Check Perfect Forward Secrecy (PFS)

Do so under Settings > Networks > + Create New Network

Name: IPsec
Purpose: Site-to-Site VPN
VPN Type: IPsec VPN
Enabled: Enable this Site-to-Site VPN
Remote Subnets:
Peer IP:
Local WAN IP:
Pre-Shared Key: <secret>
IPsec Profile: Customized

Advanced Options
Key Exchange Version: IKEv1

Encryption: AES-256
DH Group: 14
PFS: Enable Perfect Forward Secrecy
Dynamic Routing: Disabled (uncheck)

Steps: Testing & Verification

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After configuring the IPsec VPN, verify the connection/state using the following commands.

1. Verify the IPsec Security Associations (SAs) and status on the ER:

show vpn ipsec sa
peer- #1, ESTABLISHED, IKEv1, 184447c009d51f80:14cc0f13aff401c0

 local  '' @
 remote '' @
 established 237s ago, reauth in 85347s
   installed 237 ago, rekeying in 41939s, expires in 42964s
   in  cb321982,    180 bytes,     3 packets,   231s ago
   out 5d4174b1,    180 bytes,     3 packets,   231s ago

sudo ipsec statusall
Status of IKE charon daemon (strongSwan 5.2.2, Linux 3.10.14-UBNT, mips):

 uptime: 10 minutes, since Mar 12 09:05:48 2017
 malloc: sbrk 376832, mmap 0, used 269320, free 107512
 worker threads: 11 of 16 idle, 5/0/0/0 working, job queue: 0/0/0/0, scheduled: 2
 Listening IP addresses:
peer-  IKEv1
peer-   local:  [] uses pre-shared key authentication
peer-   remote: [] uses pre-shared key authentication
peer-   child: === TUNNEL
Routed Connections:
peer-{1}:  ROUTED, TUNNEL
peer-{1}: ===
Security Associations (1 up, 0 connecting):
peer-[1]: ESTABLISHED 5 minutes ago,[]...[]
peer-[1]: IKEv1 SPIs: 184447c009d51f80_i* 14cc0f13aff401c0_r, pre-shared key reauthentication in 23 hours
peer-[1]: IKE proposal: AES_CBC_256/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_2048
peer-{1}:  INSTALLED, TUNNEL, ESP SPIs: cb321982_i 5d4174b1_o
peer-{1}:  AES_CBC_128/HMAC_MD5_96, 180 bytes_i (3 pkts, 324s ago), 180 bytes_o (3 pkts, 324s ago)
peer-{1}: ===

2. Verify the ER IPsec strongSwan configuration:

sudo cat /etc/ipsec.conf
# generated by /opt/vyatta/sbin/vpn-config.pl

config setup

conn %default

conn peer-
#conn peer-

3. Capture the arrival of IKE traffic on the ER external WAN interface:

sudo tcpdump -i eth0 -n udp dst port 500   
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode

listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
IP > isakmp: phase 1 I ident
IP > isakmp: phase 1 R ident
IP > isakmp: phase 1 I ident[E]
IP > isakmp: phase 1 R ident[E]
IP > isakmp: phase 2/others I oakley-quick[E]
IP > isakmp: phase 2/others R oakley-quick[E]
info_i_25x25.png Note: This is a live capture. If there is no output that means that the traffic is either not being generated on the client, or there is something blocking the traffic upstream.

4. Capture the ER IPsec VPN logs:

sudo swanctl --log
[KNL] creating acquire job for policy[icmp/8] ===[icmp/8] with reqid {1}

[IKE] initiating Main Mode IKE_SA peer-[1] to
[ENC] generating ID_PROT request 0 [ SA V V V V ]
[NET] sending packet: from[500] to[500] (160 bytes)
[NET] received packet: from[500] to[500] (108 bytes)
[ENC] parsed ID_PROT response 0 [ SA V ]
[IKE] received NAT-T (RFC 3947) vendor ID
[ENC] generating ID_PROT request 0 [ KE No NAT-D NAT-D ]
[ENC] parsed ID_PROT response 0 [ KE No V V V V NAT-D NAT-D ]
[ENC] generating ID_PROT request 0 [ ID HASH N(INITIAL_CONTACT) ]
[ENC] parsed ID_PROT response 0 [ ID HASH ]
[IKE] IKE_SA peer-[1] established between[]...[]
[ENC] generating QUICK_MODE request 561157166 [ HASH SA No ID ID ]
[ENC] parsed QUICK_MODE response 561157166 [ HASH SA No ID ID N((24576)) ]
[IKE] CHILD_SA peer-{1} established with SPIs cb321982_i 5d4174b1_o and TS ===
info_i_25x25.png Note: This is also live capture. If there is no output that means that the traffic is either not being allowed through the firewall. Alternatively you can use the show vpn log | no-more command to view the entire IPsec log history.

5. Send traffic over the tunnel from Server1 to Host1 and vice versa:

PING ( 56(84) bytes of data.

64 bytes from icmp_seq=1 ttl=63 time=45.9 ms
64 bytes from icmp_seq=2 ttl=63 time=45.2 ms
64 bytes from icmp_seq=3 ttl=63 time=45.5 ms

PING ( 56(84) bytes of data.

64 bytes from icmp_seq=1 ttl=63 time=43.9 ms
64 bytes from icmp_seq=2 ttl=63 time=44.1 ms
64 bytes from icmp_seq=3 ttl=63 time=44.4 ms

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