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> Chapter 16 - IPsec VPN > Troubleshooting > Troubleshooting L2TP and IPsec

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Troubleshooting L2TP and IPsec

This section describes some checks and tools you can use to resolve issues with L2TP-over-IPsec VPNs.

This section includes:

Quick checks

The table below is a list of common L2TP over IPsec VPN problems and the possible solutions.

Problem What to check
IPsec tunnel does not come up. Check the logs to determine whether the failure is in Phase 1 or Phase 2.

Check the settings, including encapsulation setting, which must be transport-mode.

Check the user password.

Confirm that the user is a member of the user group assigned to L2TP.

On the Windows PC, check that the IPsec service is running and has not been disabled. See Troubleshooting L2TP and IPsec.
Tunnel connects, but there is no
communication.
Did you create an ACCEPT security policy from the public network to the protected network for the L2TP clients? See Troubleshooting L2TP and IPsec.

Mac OS X and L2TP

FortiOS allows L2TP connections with empty AVP host names and therefore Mac OS X L2TP connections can connect to the FortiGate.

Prior to FortiOS 4.0 MR3, FortiOS refused L2TP connections with empty AVP host names in compliance with RFC 2661 and RFC 3931.

Setting up logging

L2TP logging must be enabled to record L2TP events. Alert email can be configured to report L2TP errors.

Configuring FortiGate logging for L2TP over IPsec
  1. Go to Log & Report > Log Settings.
  2. Select Event Log.
  3. Select the VPN activity event check box.
  4. Select Apply.
Viewing FortiGate logs
  1. Go to Log & Report > VPN Events.
  2. Select the Log location if required.
  3. After each attempt to start the L2TP over IPsec VPN, select Refresh to view logged events.

Using the FortiGate unit debug commands

Viewing debug output for IKE and L2TP
  1. Start an SSH or Telnet session to your FortiGate unit.
  2. Enter the following CLI commands

diagnose debug application ike -1

diagnose debug application l2tp -1

diagnose debug enable

 

  1. Attempt to use the VPN and note the debug output in the SSH or Telnet session.
  2. Enter the following command to reset debug settings to default:

diagnose debug reset

Using the packet sniffer
  1. Start an SSH or Telnet session to your FortiGate unit.
  2. Enter the following CLI command

diagnose sniffer packet any icmp 4

 

  1. Attempt to use the VPN and note the debug output.
  2. Enter Ctrl-C to end sniffer operation.

Typical L2TP over IPsec session startup log entries - raw format

2010-01-11 16:39:58 log_id=0101037127 type=event subtype=ipsec pri=notice vd="root" msg="progress IPsec Phase 1" action="negotiate" rem_ip=172.20.120.151 loc_ip=172.20.120.141 rem_port=500 loc_port=500 out_intf="port1" cookies="5f6da1c0e4bbf680/d6a1009eb1dde780" user="N/A" group="N/A" xauth_user="N/A" xauth_group="N/A" vpn_tunnel="dialup_p1" status=success init=remote mode=main dir=outbound stage=1 role=responder result=OK

 

2010-01-11 16:39:58 log_id=0101037127 type=event subtype=ipsec pri=notice vd="root" msg="progress IPsec Phase 1" action="negotiate" rem_ip=172.20.120.151 loc_ip=172.20.120.141 rem_port=500 loc_port=500 out_intf="port1" cookies="5f6da1c0e4bbf680/d6a1009eb1dde780" user="N/A" group="N/A" xauth_user="N/A" xauth_group="N/A" vpn_tunnel="dialup_p1" status=success init=remote mode=main dir=outbound stage=2 role=responder result=OK

 

2010-01-11 16:39:58 log_id=0101037127 type=event subtype=ipsec pri=notice vd="root" msg="progress IPsec Phase 1" action="negotiate" rem_ip=172.20.120.151 loc_ip=172.20.120.141 rem_port=500 loc_port=500 out_intf="port1" cookies="5f6da1c0e4bbf680/d6a1009eb1dde780" user="N/A" group="N/A" xauth_user="N/A" xauth_group="N/A" vpn_tunnel="dialup_p1" status=success init=remote mode=main dir=inbound stage=3 role=responder result=DONE

 

2010-01-11 16:39:58 log_id=0101037127 type=event subtype=ipsec pri=notice vd="root" msg="progress IPsec Phase 1" action="negotiate" rem_ip=172.20.120.151 loc_ip=172.20.120.141 rem_port=500 loc_port=500 out_intf="port1" cookies="5f6da1c0e4bbf680/d6a1009eb1dde780" user="N/A" group="N/A" xauth_user="N/A" xauth_group="N/A" vpn_tunnel="dialup_p1_0" status=success init=remote mode=main dir=outbound stage=3 role=responder result=DONE

 

2010-01-11 16:39:58 log_id=0101037129 type=event subtype=ipsec pri=notice vd="root" msg="progress IPsec Phase 2" action="negotiate" rem_ip=172.20.120.151 loc_ip=172.20.120.141 rem_port=500 loc_port=500 out_intf="port1" cookies="5f6da1c0e4bbf680/d6a1009eb1dde780" user="N/A" group="N/A" xauth_user="N/A" xauth_group="N/A" vpn_tunnel="dialup_p1_0" status=success init=remote mode=quick dir=outbound stage=1 role=responder result=OK

 

2010-01-11 16:39:58 log_id=0101037133 type=event subtype=ipsec pri=notice vd="root" msg="install IPsec SA" action="install_sa" rem_ip=172.20.120.151 loc_ip=172.20.120.141 rem_port=500 loc_port=500 out_intf="port1" cookies="5f6da1c0e4bbf680/d6a1009eb1dde780" user="N/A" group="N/A" xauth_user="N/A" xauth_group="N/A" vpn_tunnel="dialup_p1_0" role=responder in_spi=61100fe2 out_spi=bd70fca1

 

2010-01-11 16:39:58 log_id=0101037139 type=event subtype=ipsec pri=notice vd="root" msg="IPsec Phase 2 status change" action="phase2-up" rem_ip=172.20.120.151 loc_ip=172.20.120.141 rem_port=500 loc_port=500 out_intf="port1" cookies="5f6da1c0e4bbf680/d6a1009eb1dde780" user="N/A" group="N/A" xauth_user="N/A" xauth_group="N/A" vpn_tunnel="dialup_p1_0" phase2_name=dialup_p2

 

2010-01-11 16:39:58 log_id=0101037138 type=event subtype=ipsec pri=notice vd="root" msg="IPsec connection status change" action="tunnel-up" rem_ip=172.20.120.151 loc_ip=172.20.120.141 rem_port=500 loc_port=500 out_intf="port1" cookies="5f6da1c0e4bbf680/d6a1009eb1dde780" user="N/A" group="N/A" xauth_user="N/A" xauth_group="N/A" vpn_tunnel="dialup_p1_0" tunnel_ip=172.20.120.151 tunnel_id=1552003005 tunnel_type=ipsec duration=0 sent=0 rcvd=0 next_stat=0 tunnel=dialup_p1_0

 

2010-01-11 16:39:58 log_id=0101037129 type=event subtype=ipsec pri=notice vd="root" msg="progress IPsec Phase 2" action="negotiate" rem_ip=172.20.120.151 loc_ip=172.20.120.141 rem_port=500 loc_port=500 out_intf="port1" cookies="5f6da1c0e4bbf680/d6a1009eb1dde780" user="N/A" group="N/A" xauth_user="N/A" xauth_group="N/A" vpn_tunnel="dialup_p1_0" status=success init=remote mode=quick dir=inbound stage=2 role=responder result=DONE

 

2010-01-11 16:39:58 log_id=0101037122 type=event subtype=ipsec pri=notice vd="root" msg="negotiate IPsec Phase 2" action="negotiate" rem_ip=172.20.120.151 loc_ip=172.20.120.141 rem_port=500 loc_port=500 out_intf="port1" cookies="5f6da1c0e4bbf680/d6a1009eb1dde780" user="N/A" group="N/A" xauth_user="N/A" xauth_group="N/A" vpn_tunnel="dialup_p1_0" status=success role=responder esp_transform=ESP_3DES esp_auth=HMAC_SHA1

 

2010-01-11 16:39:58 log_id=0103031008 type=event subtype=ppp vd=root pri=information action=connect status=success msg="Client 172.20.120.151 control connection started (id 805), assigned ip 192.168.0.50"

 

2010-01-11 16:39:58 log_id=0103029013 type=event subtype=ppp vd=root pri=notice pppd is started

 

2010-01-11 16:39:58 log_id=0103029002 type=event subtype=ppp vd=root pri=notice user="user1" local=172.20.120.141 remote=172.20.120.151 assigned=192.168.0.50 action=auth_success msg="User 'user1' using l2tp with authentication protocol MSCHAP_V2, succeeded"

 

2010-01-11 16:39:58 log_id=0103031101 type=event subtype=ppp vd=root pri=information action=tunnel-up tunnel_id=1645784497 tunnel_type=l2tp remote_ip=172.20.120.151 tunnel_ip=192.168.0.50 user="user1" group="L2TPusers" msg="L2TP tunnel established"