问题：在 debian 11 里安装了 strongswan 5.9.8-3，但Windows 10无法以ikev2方式连接，提示策略错误。查看 debian 的日志，部分内容如下：

debian charon: 13[IKE] x.x.x.x is initiating an IKE_SA debian charon:
13[CFG] received proposals:
IKE:3DES_CBC/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024,
IKE:3DES_CBC/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024,
IKE:3DES_CBC/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024,
IKE:AES_CBC_128/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024,
IKE:AES_CBC_128/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024,
IKE:AES_CBC_128/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024,
IKE:AES_CBC_192/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024,
IKE:AES_CBC_192/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024,
IKE:AES_CBC_192/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024,
IKE:AES_CBC_256/HMAC_SHA1_96/PRF_HMAC_SHA1/MODP_1024,
IKE:AES_CBC_256/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1024,
IKE:AES_CBC_256/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024,
IKE:AES_GCM_16_128/PRF_HMAC_SHA1/MODP_1024,
IKE:AES_GCM_16_128/PRF_HMAC_SHA2_256/MODP_1024,
IKE:AES_GCM_16_128/PRF_HMAC_SHA2_384/MODP_1024,
IKE:AES_GCM_16_256/PRF_HMAC_SHA1/MODP_1024,
IKE:AES_GCM_16_256/PRF_HMAC_SHA2_256/MODP_1024,
IKE:AES_GCM_16_256/PRF_HMAC_SHA2_384/MODP_1024 debian charon: 13[CFG]
configured proposals:
IKE:AES_CBC_128/AES_CBC_192/AES_CBC_256/AES_CTR_128/AES_CTR_192/AES_CTR_256/CAMELLIA_CBC_128/CAMELLIA_CBC_192/CAMELLIA_CBC_256/CAMELLIA_CTR_128/CAMELLIA_CTR_192/CAMELLIA_CTR_256/3DES_CBC/HMAC_SHA2_256_128/HMAC_SHA2_384_192/HMAC_SHA2_512_256/AES_XCBC_96/AES_CMAC_96/HMAC_SHA1_96/PRF_HMAC_SHA2_256/PRF_HMAC_SHA2_384/PRF_HMAC_SHA2_512/PRF_AES128_XCBC/PRF_AES128_CMAC/PRF_HMAC_SHA1/CURVE_25519/CURVE_448/ECP_256/ECP_384/ECP_521/ECP_256_BP/ECP_384_BP/ECP_512_BP/MODP_3072/MODP_4096/MODP_6144/MODP_8192/MODP_2048,
IKE:AES_CCM_16_128/AES_CCM_16_192/AES_CCM_16_256/AES_GCM_16_128/AES_GCM_16_192/AES_GCM_16_256/CHACHA20_POLY1305/AES_CCM_8_128/AES_CCM_8_192/AES_CCM_8_256/AES_CCM_12_128/AES_CCM_12_192/AES_CCM_12_256/AES_GCM_8_128/AES_GCM_8_192/AES_GCM_8_256/AES_GCM_12_128/AES_GCM_12_192/AES_GCM_12_256/PRF_HMAC_SHA2_256/PRF_HMAC_SHA2_384/PRF_HMAC_SHA2_512/PRF_AES128_XCBC/PRF_AES128_CMAC/PRF_HMAC_SHA1/CURVE_25519/CURVE_448/ECP_256/ECP_384/ECP_521/ECP_256_BP/ECP_384_BP/ECP_512_BP/MODP_3072/MODP_4096/MODP_6144/MODP_8192/MODP_2048

尝试：在 /etc/ipsec.conf 配置文件中，用 ike = 3des-aes128-aes192-aes256-sha1-sha256-sha384-modp1024 降低加密级别。

参考：https://docs.strongswan.org/docs/5.9/interop/windowsClients.html