Step 5: Corporate VPN with IPsec Tunnel

An IPsec IKEv2 VPN tunnel is configured between the the remote office and the VPN head end at the corporate office.

TNSR remote office IPsec VPN diagram

TNSR remote office IPsec VPN diagram

IPsec Deployment Parameters

The IPsec tunnel is built with the following parameters:

  • IP address of each tunnel endpoint, both the remote office and VPN head end.

  • Local and Remote Identity and Pre-Shared Key (PSK).

  • Compatible Phase 1 Proposal: AES128, SHA1, DH14.

  • Compatible Phase 2 Proposal: AES128GCM16, DH14.

  • IP address assigned to the tunnel interface, typically a /30 subnet.

  • IP route to direct corporate traffic over IPsec tunnel via next-hop IP.

The parameters for this deployment were captured at IPsec VPN Tunnel Parameters.

In this example, the Remote Office TNSR is behind NAT on the ISP cable mode, and using a Private IP address.

  • TNSR Outside IP: 192.168.0.53

  • TNSR Public IP: 203.0.113.65

The NAT-T feature of TNSR will recognize there is a NAT device translation in the path (traversal) and float the VPN tunnel traffic to UDP port 4500. This ensures the external NAT devices does not block the IPsec (VPN) traffic.

TNSR NAT Inbound Forwarding of IKE and ESP Packets

By default, TNSR will block inbound traffic on the outside NAT inteface. To permit the IPsec traffic, add nat static mappings to forward the inbound IPsec traffic to TNSR.

nat static mapping udp local 192.168.0.53 500 external outside 500
nat static mapping udp local 192.168.0.53 4500 external outside 4500

Note

These accessible UDP ports should be protected by an ACL, to includes source addresses in the rules when possible.

Configure IPsec Tunnel

Configure the IPsec tunnel on the remote office TNSR:

ipsec tunnel 108
  local-address 192.168.0.53
  remote-address 198.51.100.120
  crypto config-type ike
  crypto ike
    version 2
    lifetime 28800
    proposal 1
      encryption aes128
      integrity sha1
      group modp2048
      exit
    identity local
      type address
      value 203.0.113.65
      exit
    identity remote
      type address
      value 198.51.100.120
      exit
    authentication local
      round 1
        type psk
        psk AD78PPQMP00
        exit
      exit
    authentication remote
      round 1
        type psk
        psk AD78PPQMP00
        exit
      exit
    child 1
      lifetime 3600
      proposal 1
        encryption aes128gcm16
        no integrity
        group modp2048
        exit
      exit
    exit
  exit
#

Configure IP Tunnel Address and MTU

Configure a static IP address on the IPsec tunnel, and set the ip mtu to account for IPsec overhead:

interface ipip108
  ip address 172.21.254.30/30
  mtu 1400
  enable
  exit
#

To test, ping the other end of the IPsec tunnel with:

ping 172.21.254.29 source 172.21.254.30 count 5

Use this test any time you want to confirm if the IPsec Tunnel is load-bearing.

Configure IP Route to Corporate

Configure a static IP route to direct corporate traffic over the IPsec tunnel via the next-hop on the IPsec tunnel:

route table ipv4-VRF:0
  route 10.0.0.0/8
    next-hop 0 via 172.21.254.29
    exit
  exit
#

Save changes:

configuration copy running startup