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Troubleshooting IPsec VPNs

Renegotiation Errors

If a tunnel comes up initially, but then fails after a Phase 1 or Phase 2 expiration, try changing the following settings on both ends of the tunnel:

  • On the IPsec Phase 1 settings, disable NAT Traversal (NAT-T)

  • On the IPsec Phase 1 settings, enable DPD

  • On the IPsec Phase 2 settings, enter an Automatically Ping Host in the remote Phase 2 subnet.

Common Errors

The following examples have logs edited for brevity but significant messages remain.

Logging for IPsec is configured at VPN > IPsec, Advanced Settings tab. The most useful logging settings for diagnosing tunnel issues with strongSwan on pfSense® software version 2.2.x are:

  • IKE SA, IKE Child SA, and Configuration Backend on Diag

  • All others on Control

Other notable behaviors:

  • If there is an Aggressive/Main mode mismatch and the side set for Main initiates, the tunnel will still establish

  • Lifetime mismatches do not cause a failure in Phase 1 or Phase 2

Normal / OK Connection

Initiator:

charon: 09[IKE] IKE_SA con2000[11] established between 192.0.2.90[192.0.2.90]...192.0.2.74[192.0.2.74]
charon: 09[IKE] CHILD_SA con2000{2} established with SPIs cf4973bf_i c1cbfdf2_o and TS 192.168.48.0/24|/0 === 10.42.42.0/24|/0

Responder:

charon: 03[IKE] IKE_SA con1000[19] established between 192.0.2.74[192.0.2.74]...192.0.2.90[192.0.2.90]
charon: 16[IKE] CHILD_SA con1000{1} established with SPIs c1cbfdf2_i cf4973bf_o and TS 10.42.42.0/24|/0 === 192.168.48.0/24|/0

Phase 1 Main / Aggressive Mismatch

Initiator (Aggressive set, responder on Main):

charon: 15[IKE] initiating Aggressive Mode IKE_SA con2000[1] to 192.0.2.74
charon: 15[IKE] received AUTHENTICATION_FAILED error notify
charon: 13[ENC] parsed INFORMATIONAL_V1 request 1215317906 [ N(AUTH_FAILED) ]
charon: 13[IKE] received AUTHENTICATION_FAILED error notify

Responder:

charon: 13[IKE] Aggressive Mode PSK disabled for security reasons
charon: 13[ENC] generating INFORMATIONAL_V1 request 2940146627 [ N(AUTH_FAILED) ]

Phase 1 Identifier Mismatch

Initiator:

charon: 10[ENC] parsed INFORMATIONAL_V1 request 4216246776 [ HASH N(AUTH_FAILED) ]
charon: 10[IKE] received AUTHENTICATION_FAILED error notify

Responder:

charon: 12[CFG] looking for pre-shared key peer configs matching 192.0.2.74...192.0.2.90[someid]
charon: 12[IKE] no peer config found
charon: 12[ENC] generating INFORMATIONAL_V1 request 4216246776 [ HASH N(AUTH_FAILED) ]

Phase 1 Pre-Shared Key Mismatch

Initiator:

charon: 09[ENC] invalid HASH_V1 payload length, decryption failed?
charon: 09[ENC] could not decrypt payloads
charon: 09[IKE] message parsing failed

Responder:

charon: 09[ENC] invalid ID_V1 payload length, decryption failed?
charon: 09[ENC] could not decrypt payloads
charon: 09[IKE] message parsing failed

Phase 1 Encryption Algorithm Mismatch

Initiator:

charon: 14[ENC] parsed INFORMATIONAL_V1 request 3851683074 [ N(NO_PROP) ]
charon: 14[IKE] received NO_PROPOSAL_CHOSEN error notify

Responder:

charon: 14[CFG] received proposals: IKE:AES_CBC_128/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024
charon: 14[CFG] configured proposals: IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024
charon: 14[IKE] no proposal found
charon: 14[ENC] generating INFORMATIONAL_V1 request 3851683074 [ N(NO_PROP) ]

Phase 1 Hash Algorithm Mismatch

Initiator:

charon: 10[ENC] parsed INFORMATIONAL_V1 request 2774552374 [ N(NO_PROP) ]
charon: 10[IKE] received NO_PROPOSAL_CHOSEN error notify

Responder:

charon: 14[CFG] received proposals: IKE:AES_CBC_256/MODP_1024
charon: 14[CFG] configured proposals: IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024
charon: 14[IKE] no proposal found
charon: 14[ENC] generating INFORMATIONAL_V1 request 2774552374 [ N(NO_PROP) ]

Phase 1 DH Group Mismatch

Initiator:

charon: 11[ENC] parsed INFORMATIONAL_V1 request 316473468 [ N(NO_PROP) ]
charon: 11[IKE] received NO_PROPOSAL_CHOSEN error notify

Responder:

charon: 14[CFG] received proposals: IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_8192
charon: 14[CFG] configured proposals: IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024
charon: 14[IKE] no proposal found
charon: 14[ENC] generating INFORMATIONAL_V1 request 316473468 [ N(NO_PROP) ]

Phase 2 Network Mismatch

Initiator:

charon: 08[CFG] proposing traffic selectors for us:
charon: 08[CFG] 192.168.48.0/24|/0
charon: 08[CFG] proposing traffic selectors for other:
charon: 08[CFG] 10.42.43.0/24|/0
charon: 08[ENC] generating QUICK_MODE request 316948142 [ HASH SA No ID ID ]
charon: 08[NET] sending packet: from 192.0.2.90[500] to 192.0.2.74[500] (236 bytes)
charon: 08[NET] received packet: from 192.0.2.74[500] to 192.0.2.90[500] (76 bytes)
charon: 08[ENC] parsed INFORMATIONAL_V1 request 460353720 [ HASH N(INVAL_ID) ]
charon: 08[IKE] received INVALID_ID_INFORMATION error notify

Responder:

charon: 08[ENC] parsed QUICK_MODE request 2732380262 [ HASH SA No ID ID ]
charon: 08[CFG] looking for a child config for 10.42.43.0/24|/0 === 192.168.48.0/24|/0
charon: 08[CFG] proposing traffic selectors for us:
charon: 08[CFG] 10.42.42.0/24|/0
charon: 08[CFG] proposing traffic selectors for other:
charon: 08[CFG] 192.168.48.0/24|/0
charon: 08[IKE] no matching CHILD_SA config found
charon: 08[IKE] queueing INFORMATIONAL task
charon: 08[IKE] activating new tasks
charon: 08[IKE] activating INFORMATIONAL task
charon: 08[ENC] generating INFORMATIONAL_V1 request 1136605099 [ HASH N(INVAL_ID) ]

Phase 2 Encryption Algorithm Mismatch

Initiator:

charon: 14[CFG] configured proposals: ESP:AES_CBC_128/HMAC_SHA1_96/NO_EXT_SEQ
charon: 14[ENC] generating QUICK_MODE request 759760112 [ HASH SA No ID ID ]
charon: 14[NET] sending packet: from 192.0.2.90[500] to 192.0.2.74[500] (188 bytes)
charon: 14[NET] received packet: from 192.0.2.74[500] to 192.0.2.90[500] (76 bytes)
charon: 14[ENC] parsed INFORMATIONAL_V1 request 1275272345 [ HASH N(NO_PROP) ]
charon: 14[IKE] received NO_PROPOSAL_CHOSEN error notify

Responder:

charon: 13[CFG] selecting proposal:
charon: 13[CFG] no acceptable ENCRYPTION_ALGORITHM found
charon: 13[CFG] received proposals: ESP:AES_CBC_128/HMAC_SHA1_96/NO_EXT_SEQ
charon: 13[CFG] configured proposals: ESP:AES_CBC_256/HMAC_SHA1_96/NO_EXT_SEQ
charon: 13[IKE] no matching proposal found, sending NO_PROPOSAL_CHOSEN
charon: 13[IKE] queueing INFORMATIONAL task
charon: 13[IKE] activating new tasks
charon: 13[IKE] activating INFORMATIONAL task
charon: 13[ENC] generating INFORMATIONAL_V1 request 1275272345 [ HASH N(NO_PROP) ]

Phase 2 Hash Algorithm Mismatch

Initiator:

charon: 10[CFG] configured proposals: ESP:AES_CBC_256/HMAC_SHA2_512_256/NO_EXT_SEQ
charon: 10[ENC] generating QUICK_MODE request 2648029707 [ HASH SA No ID ID ]
charon: 10[NET] sending packet: from 192.0.2.90[500] to 192.0.2.74[500] (188 bytes)
charon: 10[NET] received packet: from 192.0.2.74[500] to 192.0.2.90[500] (76 bytes)
charon: 10[ENC] parsed INFORMATIONAL_V1 request 757918402 [ HASH N(NO_PROP) ]
charon: 10[IKE] received NO_PROPOSAL_CHOSEN error notify

Responder:

charon: 11[CFG] selecting proposal:
charon: 11[CFG] no acceptable INTEGRITY_ALGORITHM found
charon: 11[CFG] received proposals: ESP:AES_CBC_256/HMAC_SHA2_512_256/NO_EXT_SEQ
charon: 11[CFG] configured proposals: ESP:AES_CBC_256/HMAC_SHA1_96/NO_EXT_SEQ
charon: 11[IKE] no matching proposal found, sending NO_PROPOSAL_CHOSEN
charon: 11[IKE] queueing INFORMATIONAL task
charon: 11[IKE] activating new tasks
charon: 11[IKE] activating INFORMATIONAL task
charon: 11[ENC] generating INFORMATIONAL_V1 request 757918402 [ HASH N(NO_PROP) ]

Phase 2 PFS Mismatch

Initiator:

charon: 06[ENC] generating QUICK_MODE request 909980434 [ HASH SA No KE ID ID ]
charon: 06[NET] sending packet: from 192.0.2.90[500] to 192.0.2.74[500] (444 bytes)
charon: 06[NET] received packet: from 192.0.2.74[500] to 192.0.2.90[500] (76 bytes)
charon: 06[ENC] parsed INFORMATIONAL_V1 request 3861985833 [ HASH N(NO_PROP) ]
charon: 06[IKE] received NO_PROPOSAL_CHOSEN error notify

Responder:

charon: 08[CFG] selecting proposal:
charon: 08[CFG] no acceptable DIFFIE_HELLMAN_GROUP found
charon: 08[CFG] received proposals: ESP:AES_CBC_256/HMAC_SHA1_96/MODP_2048/NO_EXT_SEQ
charon: 08[CFG] configured proposals: ESP:AES_CBC_256/HMAC_SHA1_96/NO_EXT_SEQ
charon: 08[IKE] no matching proposal found, sending NO_PROPOSAL_CHOSEN
charon: 08[ENC] generating INFORMATIONAL_V1 request 3861985833 [ HASH N(NO_PROP) ]

Mismatched Identifier with NAT

In this case, strongSwan is set for a Peer Identifier of Peer IP address, but the remote router is actually behind NAT. In this case strongSwan expects the actual private before-NAT IP address as the identifier.

Responder:

charon: 10[IKE] remote host is behind NAT
charon: 10[IKE] IDir '192.0.2.10' does not match to '203.0.113.245'
[...]
charon: 10[CFG] looking for pre-shared key peer configs matching 198.51.100.50...203.0.113.245[192.0.2.10]

To correct this condition, change the Peer Identifier setting to IP Address and then enter the pre-NAT IP address, which in this example is 192.0.2.10.

Incorrect Destination Address

When multiple WAN IP addresses are available, such as with CARP VIPs or IP Alias VIPs, an additional failure mode can occur where the connection appears in the logs but matches bypasslan or “%any…%any”. In this case, IPsec is configured to listen to one IP address but the client is connecting to another address. For example, an IPsec Phase 1 entry may be configured to use the WAN IP address but clients are connecting to a CARP VIP. In this case, the destination address in the logs will be the VIP address and not the interface address. Confirm by checking the logs against “ipsec statusall”.

Disappearing Traffic

If IPsec traffic arrives but never appears on the IPsec interface (enc0), check for conflicting routes/interface IP addresses. For example, if an IPsec tunnel is configured with a remote network of 192.0.2.0/24 and there is a local OpenVPN server with a tunnel network of 192.0.2.0/24 then the ESP traffic may arrive, strongSwan may process the packets, but they never show up on enc0 as arriving to the OS for delivery.

Resolve the duplicate interface/route and the traffic will begin to flow.

IPsec Status Page Issues

If the IPsec status page prints errors such as:

Warning: Illegal string offset 'type' in /etc/inc/xmlreader.inc on line 116

That is a sign that the incomplete xmlreader XML parser is active, which is triggered by the presence of the file /cf/conf/use_xmlreader. This alternate parser can be faster for reading large config.xml files, but lacks certain features necessary for other areas to function well. Removing /cf/conf/use_xmlreader will return the system to the default parser immediately, which will correct the display of the IPsec status page.

IPsec Debugging

The logging options for the IPsec daemon are located under VPN > IPsec on the Advanced Settings tab and may be adjusted live without affecting the operation of IPsec tunnels. As mentioned above, the recommended setting for most common debugging is to set IKE SA, IKE Child SA, and Configuration Backend on Diag and set all others on Control.

Shrew Soft VPN Client Debugging

Open the Trace app. Stop the IKE Service, and go to File, Options. Change the log output level to debug and click OK. Start the IKE Service and attempt to connect.

Packet Loss with Certain Protocols

If packet loss is experienced only when using specific protocols (SMB, RDP, etc), MSS clamping may be required to reduce the effective MTU of the VPN. IPsec does not handle fragmented packets very well, and a reduced MTU will ensure that the packets traversing the tunnel are all of a size which can be transmitted whole. A good starting point would be 1300, and if that works, slowly increase the MSS until the breaking point is located, then back off a little from there.

MSS clamping is configured under System > Advanced on the Miscellaneous tab on pfSense software version 2.1.x and before. On pfSense software version 2.2, it is under VPN > IPsec on the Advanced Settings tab. Check the box to enable MSS Clamping for VPNs, and fill in the appropriate value.

Some Hosts Work, Others Do Not

If some hosts can communicate across a VPN tunnel and others cannot, it typically means that for some reason the packets from that client system are not being routed to the pfSense system. This could happen for a number of reasons, but the two most common are:

  • Incorrect gateway on client system: the pfSense router needs to be the gateway, or the gateway must have a static route for tunnel traffic which forwards those packets to the pfSense router.

  • Incorrect subnet mask on the client system: If the VPN subnets are close, say 192.168.0.x and 192.168.1.x, ensure that the subnet mask is 255.255.255.0 on the client systems. If one of them has an incorrect mask, such as 255.255.0.0, it will try to reach the remote systems locally and not send the packets out via the gateway.

Dropping Tunnels on ALIX/embedded

If tunnels are dropped during periods of high IPsec throughput on an ALIX or other embedded hardware, it may be necessary to disable DPD on the tunnel. When the CPU on an ALIX is tied up with sending IPsec traffic, it may not take the time to respond to a DPD request on the tunnel. As a consequence, the tunnel will fail a DPD check and be disconnected.

Crash/Panic in NIC driver with IPsec in Backtrace

If a crash occurs and the backtrace shows signs of both the NIC driver and IPsec in the backtrace, such as the following edited example:

Sleeping thread (tid 100066, pid 12) owns a non-sleepable lock
[...]
igb_mq_start_locked() at igb_mq_start_locked+0xe4/frame 0xfffffe001c39cda0
igb_mq_start() at igb_mq_start+0x224/frame 0xfffffe001c39ce10
ether_output() at ether_output+0x58d/frame 0xfffffe001c39ce80
[...]
ipsec4_common_input_cb() at ipsec4_common_input_cb+0x20d/frame 0xfffffe001c39d410
esp_input_cb() at esp_input_cb+0x4ce/frame 0xfffffe001c39d4a0
swcr_process() at swcr_process+0x89/frame 0xfffffe001c39d6d0
crypto_dispatch() at crypto_dispatch+0x6e/frame 0xfffffe001c39d700
esp_input() at esp_input+0x5a9/frame 0xfffffe001c39d790
ipsec_common_input() at ipsec_common_input+0x29a/frame 0xfffffe001c39d800
ipsec4_common_input() at ipsec4_common_input+0x91/frame 0xfffffe001c39d860
[...]
igb_rxeof() at igb_rxeof+0x698/frame 0xfffffe001c39dad0
igb_msix_que() at igb_msix_que+0x16d/frame 0xfffffe001c39db20

Try adding the following tunable to System > Advanced, System Tunables tab:

net.inet.ipsec.directdispatch=0