Technical Note: How to configure an IPsec tunnel in interface mode terminating on a Loopback interface

gfranceschi · ‎11-15-2016

Description

This article describes that to allow the tunnel to work properly in both directions, it is mandatory to add a firewall policy to allow the traffic from external (port1) to the loopback interface.

If this firewall policy is missing, the tunnel will be able to initiate only from the FortiGate 5001B with the loopback interface. The attempts to open the tunnel from the remote unit FortiGate 5001D will fail, also the rekey.

Note: If there is no firewall policy, eventually, the tunnel could be opened from the remote FortiGate 5001D if there is a session already created by the FortiGate 5001B in the session table. This will provide a random behavior.

Scope

Up to FortiOS v5.2.

Solution

Diagram:

Configuration:

FortiGate 5001B configuration: IPsec terminate on Loopback interface:

FG-5KB-5144-E-9 # show sys interface port1

config system interface

edit "port1"

set vdom "root"

set ip 10.5.17.119 255.255.240.0

set allowaccess ping https ssh http telnet

set type physical

set snmp-index 1

FG-5KB-5144-E-9 # show sys interface port2

config system interface

edit "port2"

set vdom "root"

set ip 10.70.1.119 255.255.240.0

set allowaccess ping https ssh http telnet

set type physical

set snmp-index 2

FG-5KB-5144-E-9 # show sys interface loopback

config system interface

edit "loopback"

set vdom "root"

set ip 10.11.11.11 255.255.255.255

set type loopback

set snmp-index 23

FG-5KB-5144-E-9 # show vpn ipsec phase1-interface

config vpn ipsec phase1-interface

edit "p1"

set interface "loopback"

set proposal 3des-sha1 aes128-sha1

set remote-gw 10.5.17.126

set psksecret ENC /////wOryimsvxup8kppZG5xRecwB+Az

set auto-negotiate disable

FG-5KB-5144-E-9 # show vpn ipsec phase2-interface

config vpn ipsec phase2-interface

edit "p2"

set phase1name "p1"

set proposal 3des-sha1 aes128-sha1

set src-subnet 10.70.0.0 255.255.240.0

set dst-subnet 10.134.0.0 255.255.240.0

FG-5KB-5144-E-9 # show firewall address local70

config firewall address

edit "local70"

set uuid 8a967910-a58b-51e6-b971-75521301d770

set subnet 10.70.0.0 255.255.240.0

FG-5KB-5144-E-9 # show firewall address remote134

config firewall address

edit "remote134"

set uuid 8a967910-a58b-51e6-b971-75521301d780

set subnet 10.134.0.0 255.255.240.0

FG-5KB-5144-E-9 # show firewall address loopback11

config firewall address

edit "loopback11"

set uuid 8ab68336-a58b-51e6-0542-ae24ae5418a5

set subnet 10.11.11.11 255.255.255.255

FG-5KB-5144-E-9 # show firewall policy

config firewall policy

edit 1

set uuid a2b6b672-a58b-51e6-3fd6-8dc39312bef1

set srcintf "port2"

set dstintf "p1"

set srcaddr "local70"

set dstaddr "remote134"

set action accept

set schedule "always"

set service "ALL"

set uuid a3060b78-a58b-51e6-1a1d-5ae5d4c4584b

set srcintf "p1"

set dstintf "port2"

set srcaddr "remote134"

set dstaddr "local70"

set action accept

set schedule "always"

set service "ALL"

edit 3

set uuid a35563c6-a58b-51e6-5ee0-67578f665355

set srcintf "port1"

set dstintf "loopback"

set srcaddr "all"

set dstaddr "loopback11"

set action accept

set schedule "always"

set service "IKE"

set logtraffic all

set logtraffic-start enable

config system interface

edit "mgmt1"

set vdom "root"

set ip 10.5.17.126 255.255.240.0

set allowaccess ping https ssh http telnet

set type physical

set snmp-index 10

config system interface

edit "phase1"

set vdom "root"

set type tunnel

set snmp-index 22

set interface "mgmt1"

config vpn ipsec phase1-interface

edit "phase1"

set interface "mgmt1"

set proposal 3des-sha1 aes128-sha1

set remote-gw 10.11.11.11

set psksecret ENC dmFyL8GXi28fONH6tP4+

set auto-negotiate disable

config vpn ipsec phase2-interface

edit "phase2"

set phase1name "phase1"

set proposal 3des-sha1 aes128-sha1

set src-subnet 10.134.0.0 255.255.240.0

set dst-subnet 10.70.0.0 255.255.240.0

edit "remote70"

set subnet 10.70.0.0 255.255.240.0

set subnet 10.134.0.0 255.255.240.0

config firewall policy

edit 1

set uuid f19f4ada-a2d2-51e6-86c7-b655bc7acc90

set srcintf "phase1"

set dstintf "port3"

set srcaddr "remote70"

set dstaddr "local134"

set action accept

set schedule "always"

set service "ALL"

set uuid 2ad09f98-a2d3-51e6-194e-7de97d90d457

set srcintf "port3"

set dstintf "phase1"

set srcaddr "local134"

set dstaddr "remote70"

set action accept

set schedule "always"

set service "ALL"

config router static

edit 2

set dst 10.70.0.0 255.255.240.0

set device "phase1"

set dst 10.11.11.11 255.255.255.255

set gateway 10.5.17.119

set device "mgmt1"

Troubleshooting.

If firewall policy id 3 is created, it allows the IPsec traffic initiated by the remote unit to reach the loopback interface of the FortiGate 5001B.

FortiGate 5001D:

FG-5KD-5144C-ORA-6 # get ro info ro all

Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP

O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default

C 10.5.16.0/20 is directly connected, mgmt1

C 10.134.0.0/20 is directly connected, port3

S 10.11.11.11/32 [10/0] via 10.5.17.119, mgmt1

S 10.70.0.0/20 [10/0] is directly connected, phase1

FortiGate 5001B:

FG-5KB-5144-E-9 # get ro info ro all

Codes: K - kernel, C - connected, S - static, R - RIP, B - BGP

O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default

C 10.5.16.0/20 is directly connected, port1

C 10.70.0.0/20 is directly connected, port2

C 10.11.11.11/32 is directly connected, loopback

S 10.134.0.0/20 [10/0] is directly connected, p1

FG-5KB-5144-E-9 # diagnose debug flow show console enable

show trace messages on console

FG-5KB-5144-E-9 # diagnose debug flow filter dport 500

FG-5KB-5144-E-9 # diagnose debug flow trace start 50

FG-5KB-5144-E-9 # di debug enable

FG-5KB-5144-E-9 # diagnose debug console timestamp enable

FG-5KB-5144-E-9 # diagnose debug sniffer packet any "udp port 500" 4

interfaces=[any]

filters=[udp port 500]

2016-11-08 14:19:13 id=20085 trace_id=172 func=print_pkt_detail line=4476 msg="vd-root received a packet(proto=17, 10.5.17.126:500->10.11.11.11:500) from port1. "

2016-11-08 14:19:13 id=20085 trace_id=172 func=init_ip_session_common line=4629 msg="allocate a new session-00023e24"

85.413252 port1 in 10.5.17.126.500 -> 10.11.11.11.500: udp 404

2016-11-08 14:19:13 id=20085 trace_id=173 func=print_pkt_detail line=4476 msg="vd-root received a packet(proto=17, 10.11.11.11:500->10.5.17.126:500) from local. "

85.413447 port1 out 10.11.11.11.500 -> 10.5.17.126.500: udp 188

2016-11-08 14:19:13 id=20085 trace_id=173 func=resolve_ip_tuple_fast line=4539 msg="Find an existing session, id-00023e24, reply direction"

2016-11-08 14:19:13 id=20085 trace_id=174 func=print_pkt_detail line=4476 msg="vd-root received a packet(proto=17, 10.5.17.126:500->10.11.11.11:500) from port1. "

85.414237 port1 in 10.5.17.126.500 -> 10.11.11.11.500: udp 356

If there is no firewall policy 3 from the external interface to the loopback interface, the traffic is rejected by the FortiGate policy check.

2016-11-08 17:21:18 id=13 trace_id=101 func=print_pkt_detail line=4307 msg="vd-BM0FWIRR01 received a packet(proto=17, 10.5.17.126:500->10.11.11.11:500) from port1. "

2016-11-08 17:21:18 id=13 trace_id=101 func=init_ip_session_common line=4463 msg="allocate a new session-d75bd206"

2016-11-08 17:21:18 id=13 trace_id=101 func=__iprope_tree_check line=534 msg="use addr/intf hash, len=2"

2016-11-08 17:21:18 id=13 trace_id=101 func=fw_local_in_handler line=360 msg="iprope_in_check() check failed on policy 0, drop"

If 'set local-in-deny-unicast' is enabled (under config log setting), FortiGate would generate logs for the denied IKE requests (the allowed traffic will also be displayed with the corresponding policy ID). See 'Sample Logging Screenshot.PNG' for an example of logs that FortiGate will generate with this setting in place.