IKEv2 client VPN: unexpected no proposal match

PetrH

Hello,
I can't figure out why the following connection attempt case (Android 11 client, IKEv2 MSCHAPv2 VPN) ends up with: received proposals unacceptable

Proposals are:
received proposals:
IKE:AES_CBC_256/AES_CBC_192/AES_CBC_128/HMAC_SHA2_512_256/HMAC_SHA2_384_192/HMAC_SHA2_256_128/AES_XCBC_96/PRF_HMAC_SHA1/PRF_AES128_XCBC/MODP_4096/MODP_3072/MODP_2048
IKE:AES_GCM_16_256/AES_GCM_12_256/AES_GCM_8_256/AES_GCM_16_192/AES_GCM_12_192/AES_GCM_8_192/AES_GCM_16_128/AES_GCM_12_128/AES_GCM_8_128/PRF_HMAC_SHA1/PRF_AES128_XCBC/MODP_4096/MODP_3072/MODP_2048

configured proposals:
IKE:AES_GCM_16_128/PRF_HMAC_SHA2_256/MODP_2048
IKE:AES_CBC_256/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_2048
IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_2048
IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024

And I'd expect a match on the highlighted combination.
Does anyone have any idea why it ends up with no match?

05[NET] <13> received packet: from 1.2.3.4[65227] to 4.3.2.1[500] (940 bytes)
05[ENC] <13> parsed IKE_SA_INIT request 0 [ SA KE No N(NATD_S_IP) N(NATD_D_IP) N(FRAG_SUP) N(HASH_ALG) ]
05[CFG] <13> looking for an IKEv2 config for 4.3.2.1...1.2.3.4
05[CFG] <13>   candidate: 4.3.2.1...0.0.0.0/0, ::/0, prio 1052
05[CFG] <13> found matching ike config: 4.3.2.1...0.0.0.0/0, ::/0 with prio 1052
05[IKE] <13> 1.2.3.4 is initiating an IKE_SA
05[IKE] <13> IKE_SA (unnamed)[13] state change: CREATED => CONNECTING
05[CFG] <13> selecting proposal:
05[CFG] <13>   no acceptable ENCRYPTION_ALGORITHM found
05[CFG] <13> selecting proposal:
05[CFG] <13>   no acceptable PSEUDO_RANDOM_FUNCTION found
05[CFG] <13> selecting proposal:
05[CFG] <13>   no acceptable PSEUDO_RANDOM_FUNCTION found
05[CFG] <13> selecting proposal:
05[CFG] <13>   no acceptable ENCRYPTION_ALGORITHM found
05[CFG] <13> selecting proposal:
05[CFG] <13>   no acceptable INTEGRITY_ALGORITHM found
05[CFG] <13> selecting proposal:
05[CFG] <13>   no acceptable ENCRYPTION_ALGORITHM found
05[CFG] <13> selecting proposal:
05[CFG] <13>   no acceptable INTEGRITY_ALGORITHM found
05[CFG] <13> selecting proposal:
05[CFG] <13>   no acceptable ENCRYPTION_ALGORITHM found
05[CFG] <13> received proposals: IKE:AES_CBC_256/AES_CBC_192/AES_CBC_128/HMAC_SHA2_512_256/HMAC_SHA2_384_192/HMAC_SHA2_256_128/AES_XCBC_96/PRF_HMAC_SHA1/PRF_AES128_XCBC/MODP_4096/MODP_3072/MODP_2048, IKE:AES_GCM_16_256/AES_GCM_12_256/AES_GCM_8_256/AES_GCM_16_192/AES_GCM_12_192/AES_GCM_8_192/AES_GCM_16_128/AES_GCM_12_128/AES_GCM_8_128/PRF_HMAC_SHA1/PRF_AES128_XCBC/MODP_4096/MODP_3072/MODP_2048
05[CFG] <13> configured proposals: IKE:AES_GCM_16_128/PRF_HMAC_SHA2_256/MODP_2048, IKE:AES_CBC_256/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_2048, IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_2048, IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024
05[CFG] <13> looking for IKEv2 configs for 4.3.2.1...1.2.3.4
05[CFG] <13>   candidate: 4.3.2.1...0.0.0.0/0, ::/0, prio 1052
05[CFG] <13> received supported signature hash algorithms: sha256 sha384 sha512
05[IKE] <13> remote host is behind NAT
05[IKE] <13> received proposals unacceptable
05[ENC] <13> generating IKE_SA_INIT response 0 [ N(NO_PROP) ]
05[NET] <13> sending packet: from 4.3.2.1[500] to 1.2.3.4[65227] (36 bytes)
05[IKE] <13> IKE_SA (unnamed)[13] state change: CONNECTING => DESTROYING

jimp

@petrh said in IKEv2 client VPN: unexpected no proposal match:

PRF_HMAC_SHA2_256

The received proposal does not include PRF_HMAC_SHA2_256, and the only entry which matches most of the other parts requires PRF_HMAC_SHA2_256.

You can check the box to set a specific alternate PRF and then choose SHA1 for that which should work.

Or configure the remote side to allow a SHA2 PRF.

PetrH

@jimp Great, thanks for the hint. I was thinking the right direction, but missed the setting. I look more thoroughly again and found it.