# tcpdump -nvs1400 -i xl1 port 500 
tcpdump: listening on xl1, link-type EN10MB
11:43:55.225626 201.12.35.53.500 > 201.77.95.20.500: [udp sum ok] isakmp v1.0 exchange ID_PROT
        cookie: 9f74658ec3235d33->0000000000000000 msgid: 00000000 len: 176
        payload: SA len: 48 DOI: 1(IPSEC) situation: IDENTITY_ONLY 
            payload: PROPOSAL len: 36 proposal: 1 proto: ISAKMP spisz: 0 xforms: 1
                payload: TRANSFORM len: 28
                    transform: 0 ID: ISAKMP
                        attribute ENCRYPTION_ALGORITHM = 3DES_CBC
                        attribute HASH_ALGORITHM = SHA
                        attribute AUTHENTICATION_METHOD = PRE_SHARED
                        attribute GROUP_DESCRIPTION = MODP_1024
                        attribute LIFE_TYPE = SECONDS
        payload: VENDOR len: 20 (supports OpenBSD-4.0)
        payload: VENDOR len: 20 (supports v2 NAT-T, draft-ietf-ipsec-nat-t-ike-02)
        payload: VENDOR len: 20 (supports v3 NAT-T, draft-ietf-ipsec-nat-t-ike-03)
        payload: VENDOR len: 20 (supports NAT-T, RFC 3947)
        payload: VENDOR len: 20 (supports DPD v1.0) (ttl 64, id 6300, len 204)
11:43:55.280232 201.77.95.20.500 > 201.12.35.53.500: [udp sum ok] isakmp v1.0 exchange INFO
        cookie: 9f74658ec3235d33->0000000000000000 msgid: 0ca811ef len: 40
        payload: NOTIFICATION len: 12
            notification: NO PROPOSAL CHOSEN (DF) (ttl 55, id 5304, len 68)
11:44:02.241258 201.12.35.53.500 > 201.77.95.20.500: [udp sum ok] isakmp v1.0 exchange ID_PROT
        cookie: 9f74658ec3235d33->0000000000000000 msgid: 00000000 len: 176
        payload: SA len: 48 DOI: 1(IPSEC) situation: IDENTITY_ONLY 
            payload: PROPOSAL len: 36 proposal: 1 proto: ISAKMP spisz: 0 xforms: 1
                payload: TRANSFORM len: 28
                    transform: 0 ID: ISAKMP
                        attribute ENCRYPTION_ALGORITHM = 3DES_CBC
                        attribute HASH_ALGORITHM = SHA
                        attribute AUTHENTICATION_METHOD = PRE_SHARED
                        attribute GROUP_DESCRIPTION = MODP_1024
                        attribute LIFE_TYPE = SECONDS
        payload: VENDOR len: 20 (supports OpenBSD-4.0)
        payload: VENDOR len: 20 (supports v2 NAT-T, draft-ietf-ipsec-nat-t-ike-02)
        payload: VENDOR len: 20 (supports v3 NAT-T, draft-ietf-ipsec-nat-t-ike-03)
        payload: VENDOR len: 20 (supports NAT-T, RFC 3947)
        payload: VENDOR len: 20 (supports DPD v1.0) (ttl 64, id 63724, len 204)
11:44:11.251509 201.12.35.53.500 > 201.77.95.20.500: [udp sum ok] isakmp v1.0 exchange ID_PROT
        cookie: 9f74658ec3235d33->0000000000000000 msgid: 00000000 len: 176
        payload: SA len: 48 DOI: 1(IPSEC) situation: IDENTITY_ONLY 
            payload: PROPOSAL len: 36 proposal: 1 proto: ISAKMP spisz: 0 xforms: 1
                payload: TRANSFORM len: 28
                    transform: 0 ID: ISAKMP
                        attribute ENCRYPTION_ALGORITHM = 3DES_CBC
                        attribute HASH_ALGORITHM = SHA
                        attribute AUTHENTICATION_METHOD = PRE_SHARED
                        attribute GROUP_DESCRIPTION = MODP_1024
                        attribute LIFE_TYPE = SECONDS
        payload: VENDOR len: 20 (supports OpenBSD-4.0)
        payload: VENDOR len: 20 (supports v2 NAT-T, draft-ietf-ipsec-nat-t-ike-02)
        payload: VENDOR len: 20 (supports v3 NAT-T, draft-ietf-ipsec-nat-t-ike-03)
        payload: VENDOR len: 20 (supports NAT-T, RFC 3947)
        payload: VENDOR len: 20 (supports DPD v1.0) (ttl 64, id 37766, len 204)