regression: failing connection for clients with ikev1&psk (fritzbox)

Hello Tobias,

Thanks for filing this bug.

Would you be able to provide shorter reproducers for each of the issues you are experiencing (minimal setups and configuration files) so we can better assist in debugging and finding a root cause? Then when we can confirm we are dealing with 2 different issues, we can split this in 2 different bugs as well.

@Tobias, in case you didn't know combining Aggressive mode and PreShared key is insecure and discouraged by upstream: https://wiki.strongswan.org/projects/1/wiki/FAQ#Aggressive-Mode

If you can, it's recommended to switch to IKEv2.

@Simon: Yes, but like i said this is about fritzbox devices which can't do anything else: https://wiki.strongswan.org/projects/strongswan/wiki/AVM_FRITZ_(FRITZ!Box_)_brand_devices

Minimal config with a fresh install of strongswan-starter:

/etc/ipsec.conf:

conn vpn-user
    auto=add

    leftsubnet=172.17.0.0/16

    rightsubnet=172.17.101.0/24
    rightsourceip=172.17.101.1/24

    leftauth=psk
    rightauth=psk
    <email address hidden>
    rightid=keyid:<email address hidden>

    aggressive=yes
    keyexchange=ikev1
    ike=aes256-sha-modp1024
    esp=aes256-sha1-modp1024

    dpdaction=clear

/etc/ipsec.secrets

   <email address hidden> : PSK "eiW?ee3Ay3quoh7EXAMPLE"

/etc/strongswan.d/custom.conf

   charon {
      i_dont_care_about_security_and_use_aggressive_mode_psk=yes
   }

Client is a AVM Fritz!Box 7360 with the latest firmware 06.87

Result:

    10[NET] received packet: from <CLIENT-IP>[500] to <HOST-IP>[500] (672 bytes)
    10[ENC] parsed AGGRESSIVE request 0 [ SA KE No ID V V V V V V ]
    10[IKE] received XAuth vendor ID
    10[IKE] received DPD vendor ID
    10[IKE] received NAT-T (RFC 3947) vendor ID
    10[IKE] received draft-ietf-ipsec-nat-t-ike-02\n vendor ID
    10[IKE] received draft-ietf-ipsec-nat-t-ike-03 vendor ID
    10[ENC] received unknown vendor ID: a2:22:6f:c3:64:50:0f:56:34:ff:77:db:3b:74:f4:1b
    10[IKE] <CLIENT-IP> is initiating a Aggressive Mode IKE_SA
    10[IKE] <CLIENT-IP> is initiating a Aggressive Mode IKE_SA
    10[CFG] selected proposal: IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024
    10[CFG] looking for pre-shared key peer configs matching <HOST-IP>...<CLIENT-IP>[<email address hidden>]
    10[CFG] selected peer config "vpn-user"
    10[IKE] no shared key found for '%any'[<HOST-IP>] - '<email address hidden>'[<CLIENT-IP>]
    10[IKE] no shared key found for <HOST-IP> - <CLIENT-IP>
    10[ENC] generating INFORMATIONAL_V1 request 1178843998 [ N(INVAL_KE) ]
    10[NET] sending packet: from <HOST-IP>[500] to <CLIENT-IP>[500] (56 bytes)
    11[NET] received packet: from <CLIENT-IP>[500] to <HOST-IP>[500] (672 bytes)
    11[ENC] parsed AGGRESSIVE request 0 [ SA KE No ID V V V V V V ]
    11[IKE] received XAuth vendor ID
    11[IKE] received DPD vendor ID
    11[IKE] received NAT-T (RFC 3947) vendor ID
    11[IKE] received draft-ietf-ipsec-nat-t-ike-02\n vendor ID
    11[IKE] received draft-ietf-ipsec-nat-t-ike-03 vendor ID
    11[ENC] received unknown vendor ID: a2:22:6f:c3:64:50:0f:56:34:ff:77:db:3b:74:f4:1b
    11[IKE] <CLIENT-IP> is initiating a Aggressive Mode IKE_SA
    11[IKE] <CLIENT-IP> is initiating a Aggressive Mode IKE_SA
    11[CFG] selected proposal: IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024
    11[CFG] looking for pre-shared key peer configs matching <HOST-IP>...<CLIENT-IP>[<email address hidden>]
    11[CFG] selected peer config "vpn-user"
    11[IKE] no shared key found for '%any'[<HOST-IP>] - '<email address hidden>'[<CLIENT-IP>]
    11[IKE] no shared key found for <HOST-IP> - <CLIENT-IP>
    11[ENC] generating INFORMATIONAL_V1 request 102147980 [ N(INVAL_KE) ]
    11[NET] sending packet: from <HOST-IP>[500] to <CLIENT-IP>[500] (56 bytes)

Now when changing the ipsecrets.conf to:

    <email address hidden> %any : PSK "eiW?ee3Ay3quoh7EXAMPLE"

(As Reminder: Now every connection would use this PSK so will only work for a single client ...)
Connection succeed but is killed by dea...

keyid:<email address hidden> and <email address hidden> are not the same thing. The latter is parsed as identity of type USER_FQDN/RFC822 and won't match an identity of type KEY_ID. So you have to use the same prefix in ipsec.secrets too.

No idea why the FRITZ!Box would only reply to the first DPD.

@Tobias: Thanks.
I've always wondered why this config sometimes used keyid (I'am just keeping the system alive without any real knowledge in the field)

Seems like strongswan got more stricter with this somewhere between 5.8.2 and 5.9.5 without it appearing as a breaking change in the change log.

18.04 actually shipped 5.6.2 (5.8.2 was shipped with 20.04), but this particular aspect has not changed between either of these versions (the type of identities always had to match).

But what did change is that the actual local identity of the IKE_SA is now used for the PSK lookup, not any potentially configured one. So it was the identity you configured in leftid that matched the PSK in older versions, never the remote identity. When using aggressive mode, the local identity is now %any at this point and the PSK won't match anymore. I've pushed a fix for this to the aggressive-local-id branch.

Explanation of Tobias Bruner on required config changed fixed this for me somehow.

The Problem with the failing DPD on Fritzbox is still presented i worked around with a manual keepalive using a simple ping cronjob.