> NAT где-то используется для второго провайдера?  NAT-traversal на сервере включен?
> Пробуйте менять настройки клиента - TCP/UDP
> Проверяйте что протоколы gre/esp не блокируются

И в одном случае и в другом компьютеру выдается частный адрес провайдером, т.е. нат идет на стороне провайдера.

Вот что в конце постоянно повторяется на циске, если включить debug crypto isakmp

.Feb 29 14:35:58.471: ISAKMP:(0:5:SW:1):purging node -464526915
.Feb 29 14:35:59.179: ISAKMP (0:134217733): received packet from 95.140.92.16 dport 4500 sport 26499 Global (R) QM_IDLE
.Feb 29 14:35:59.179: ISAKMP: set new node 1619324510 to QM_IDLE
.Feb 29 14:35:59.183: ISAKMP:(0:5:SW:1): processing HASH payload. message ID = 1619324510
.Feb 29 14:35:59.183: ISAKMP:(0:5:SW:1): processing NOTIFY DPD/R_U_THERE protocol 1
        spi 0, message ID = 1619324510, sa = 82CB85C4
.Feb 29 14:35:59.183: ISAKMP:(0:5:SW:1):deleting node 1619324510 error FALSE reason "Informational (in) state 1"
.Feb 29 14:35:59.183: ISAKMP:(0:5:SW:1):Input = IKE_MESG_FROM_PEER, IKE_INFO_NOTIFY
.Feb 29 14:35:59.183: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

.Feb 29 14:35:59.187: ISAKMP:(0:5:SW:1):DPD/R_U_THERE received from peer 95.140.92.16, sequence 0xCADD4E90
.Feb 29 14:35:59.187: ISAKMP: set new node -629883989 to QM_IDLE
.Feb 29 14:35:59.191: ISAKMP:(0:5:SW:1):Sending NOTIFY DPD/R_U_THERE_ACK protocol 1
        spi 2192638968, message ID = -629883989
.Feb 29 14:35:59.191: ISAKMP:(0:5:SW:1): seq. no 0xCADD4E90
.Feb 29 14:35:59.191: ISAKMP:(0:5:SW:1): sending packet to 95.140.92.16 my_port 4500 peer_port 12435 (R) QM_IDLE
.Feb 29 14:35:59.191: ISAKMP:(0:5:SW:1):purging node -629883989
.Feb 29 14:35:59.195: ISAKMP:(0:5:SW:1):Input = IKE_MESG_FROM_PEER, IKE_MESG_KEEP_ALIVE
.Feb 29 14:35:59.195: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

.Feb 29 14:36:03.543: ISAKMP:(0:5:SW:1):purging node -710359380
.Feb 29 14:36:04.247: ISAKMP (0:134217733): received packet from 95.140.92.16 dport 4500 sport 26499 Global (R) QM_IDLE
.Feb 29 14:36:04.247: ISAKMP: set new node -1118440403 to QM_IDLE
.Feb 29 14:36:04.251: ISAKMP:(0:5:SW:1): processing HASH payload. message ID = -1118440403
.Feb 29 14:36:04.251: ISAKMP:(0:5:SW:1): processing NOTIFY DPD/R_U_THERE protocol 1
        spi 0, message ID = -1118440403, sa = 82CB85C4
.Feb 29 14:36:04.251: ISAKMP:(0:5:SW:1):deleting node -1118440403 error FALSE reason "Informational (in) state 1"
.Feb 29 14:36:04.255: ISAKMP:(0:5:SW:1):Input = IKE_MESG_FROM_PEER, IKE_INFO_NOTIFY
.Feb 29 14:36:04.255: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

.Feb 29 14:36:04.255: ISAKMP:(0:5:SW:1):DPD/R_U_THERE received from peer 95.140.92.16, sequence 0xCADD4E91
.Feb 29 14:36:04.255: ISAKMP: set new node -2122983767 to QM_IDLE
.Feb 29 14:36:04.259: ISAKMP:(0:5:SW:1):Sending NOTIFY DPD/R_U_THERE_ACK protocol 1
        spi 2192638968, message ID = -2122983767
.Feb 29 14:36:04.259: ISAKMP:(0:5:SW:1): seq. no 0xCADD4E91
.Feb 29 14:36:04.259: ISAKMP:(0:5:SW:1): sending packet to 95.140.92.16 my_port 4500 peer_port 12435 (R) QM_IDLE
.Feb 29 14:36:04.263: ISAKMP:(0:5:SW:1):purging node -2122983767
.Feb 29 14:36:04.263: ISAKMP:(0:5:SW:1):Input = IKE_MESG_FROM_PEER, IKE_MESG_KEEP_ALIVE
.Feb 29 14:36:04.263: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

.Feb 29 14:36:08.615: ISAKMP:(0:5:SW:1):purging node -127477789
.Feb 29 14:36:09.319: ISAKMP (0:134217733): received packet from 95.140.92.16 dport 4500 sport 26499 Global (R) QM_IDLE
.Feb 29 14:36:09.319: ISAKMP: set new node 478458228 to QM_IDLE
.Feb 29 14:36:09.319: ISAKMP:(0:5:SW:1): processing HASH payload. message ID = 478458228
.Feb 29 14:36:09.323: ISAKMP:(0:5:SW:1): processing NOTIFY DPD/R_U_THERE protocol 1
        spi 0, message ID = 478458228, sa = 82CB85C4
.Feb 29 14:36:09.323: ISAKMP:(0:5:SW:1):deleting node 478458228 error FALSE reason "Informational (in) state 1"
.Feb 29 14:36:09.323: ISAKMP:(0:5:SW:1):Input = IKE_MESG_FROM_PEER, IKE_INFO_NOTIFY
.Feb 29 14:36:09.323: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

.Feb 29 14:36:09.327: ISAKMP:(0:5:SW:1):DPD/R_U_THERE received from peer 95.140.92.16, sequence 0xCADD4E92
.Feb 29 14:36:09.327: ISAKMP: set new node 471288413 to QM_IDLE
.Feb 29 14:36:09.327: ISAKMP:(0:5:SW:1):Sending NOTIFY DPD/R_U_THERE_ACK protocol 1
        spi 2192638968, message ID = 471288413
.Feb 29 14:36:09.327: ISAKMP:(0:5:SW:1): seq. no 0xCADD4E92
.Feb 29 14:36:09.331: ISAKMP:(0:5:SW:1): sending packet to 95.140.92.16 my_port 4500 peer_port 12435 (R) QM_IDLE
.Feb 29 14:36:09.331: ISAKMP:(0:5:SW:1):purging node 471288413
.Feb 29 14:36:09.331: ISAKMP:(0:5:SW:1):Input = IKE_MESG_FROM_PEER, IKE_MESG_KEEP_ALIVE
.Feb 29 14:36:09.331: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

.Feb 29 14:36:13.687: ISAKMP:(0:5:SW:1):purging node 253389389
.Feb 29 14:36:14.391: ISAKMP (0:134217733): received packet from 95.140.92.16 dport 4500 sport 26499 Global (R) QM_IDLE
.Feb 29 14:36:14.391: ISAKMP: set new node -552724267 to QM_IDLE
.Feb 29 14:36:14.391: ISAKMP:(0:5:SW:1): processing HASH payload. message ID = -552724267
.Feb 29 14:36:14.395: ISAKMP:(0:5:SW:1): processing NOTIFY DPD/R_U_THERE protocol 1
        spi 0, message ID = -552724267, sa = 82CB85C4
.Feb 29 14:36:14.395: ISAKMP:(0:5:SW:1):deleting node -552724267 error FALSE reason "Informational (in) state 1"
.Feb 29 14:36:14.395: ISAKMP:(0:5:SW:1):Input = IKE_MESG_FROM_PEER, IKE_INFO_NOTIFY
.Feb 29 14:36:14.395: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

.Feb 29 14:36:14.399: ISAKMP:(0:5:SW:1):DPD/R_U_THERE received from peer 95.140.92.16, sequence 0xCADD4E93
.Feb 29 14:36:14.399: ISAKMP: set new node -1190697414 to QM_IDLE
.Feb 29 14:36:14.399: ISAKMP:(0:5:SW:1):Sending NOTIFY DPD/R_U_THERE_ACK protocol 1
        spi 2192638968, message ID = -1190697414
.Feb 29 14:36:14.399: ISAKMP:(0:5:SW:1): seq. no 0xCADD4E93
.Feb 29 14:36:14.403: ISAKMP:(0:5:SW:1): sending packet to 95.140.92.16 my_port 4500 peer_port 12435 (R) QM_IDLE
.Feb 29 14:36:14.403: ISAKMP:(0:5:SW:1):purging node -1190697414
.Feb 29 14:36:14.403: ISAKMP:(0:5:SW:1):Input = IKE_MESG_FROM_PEER, IKE_MESG_KEEP_ALIVE
.Feb 29 14:36:14.403: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

.Feb 29 14:36:18.751: ISAKMP:(0:5:SW:1):purging node 477552065
.Feb 29 14:36:19.459: ISAKMP (0:134217733): received packet from 95.140.92.16 dport 4500 sport 26499 Global (R) QM_IDLE
.Feb 29 14:36:19.459: ISAKMP: set new node 466751117 to QM_IDLE
.Feb 29 14:36:19.463: ISAKMP:(0:5:SW:1): processing HASH payload. message ID = 466751117
.Feb 29 14:36:19.463: ISAKMP:(0:5:SW:1): processing NOTIFY DPD/R_U_THERE protocol 1
        spi 0, message ID = 466751117, sa = 82CB85C4
.Feb 29 14:36:19.463: ISAKMP:(0:5:SW:1):deleting node 466751117 error FALSE reason "Informational (in) state 1"
.Feb 29 14:36:19.463: ISAKMP:(0:5:SW:1):Input = IKE_MESG_FROM_PEER, IKE_INFO_NOTIFY
.Feb 29 14:36:19.463: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

.Feb 29 14:36:19.467: ISAKMP:(0:5:SW:1):DPD/R_U_THERE received from peer 95.140.92.16, sequence 0xCADD4E94
.Feb 29 14:36:19.467: ISAKMP: set new node -48663732 to QM_IDLE
.Feb 29 14:36:19.471: ISAKMP:(0:5:SW:1):Sending NOTIFY DPD/R_U_THERE_ACK protocol 1
        spi 2192638968, message ID = -48663732
.Feb 29 14:36:19.471: ISAKMP:(0:5:SW:1): seq. no 0xCADD4E94
.Feb 29 14:36:19.471: ISAKMP:(0:5:SW:1): sending packet to 95.140.92.16 my_port 4500 peer_port 12435 (R) QM_IDLE
.Feb 29 14:36:19.471: ISAKMP:(0:5:SW:1):purging node -48663732
.Feb 29 14:36:19.475: ISAKMP:(0:5:SW:1):Input = IKE_MESG_FROM_PEER, IKE_MESG_KEEP_ALIVE
.Feb 29 14:36:19.475: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

.Feb 29 14:36:23.823: ISAKMP:(0:5:SW:1):purging node -586312068
.Feb 29 14:36:24.535: ISAKMP (0:134217733): received packet from 95.140.92.16 dport 4500 sport 26499 Global (R) QM_IDLE
.Feb 29 14:36:24.535: ISAKMP: set new node 1873201770 to QM_IDLE
.Feb 29 14:36:24.539: ISAKMP:(0:5:SW:1): processing HASH payload. message ID = 1873201770
.Feb 29 14:36:24.539: ISAKMP:(0:5:SW:1): processing DELETE payload. message ID = 1873201770
.Feb 29 14:36:24.539: ISAKMP:(0:5:SW:1):peer does not do paranoid keepalives.

.Feb 29 14:36:24.539: ISAKMP:(0:5:SW:1):peer does not do paranoid keepalives.

.Feb 29 14:36:24.539: ISAKMP:(0:5:SW:1):deleting node 1873201770 error FALSE reason "Informational (in) state 1"
.Feb 29 14:36:24.543: ISAKMP (0:134217733): received packet from 95.140.92.16 dport 4500 sport 26499 Global (R) QM_IDLE
.Feb 29 14:36:24.543: ISAKMP: set new node 1280949153 to QM_IDLE
.Feb 29 14:36:24.543: ISAKMP:(0:5:SW:1): processing HASH payload. message ID = 1280949153
.Feb 29 14:36:24.547: ISAKMP:received payload type 18
.Feb 29 14:36:24.547: ISAKMP:(0:5:SW:1): processing DELETE_WITH_REASON payload, message ID = 1280949153, reason: DELETE_BY_USER_COMMAND
.Feb 29 14:36:24.547: ISAKMP:(0:5:SW:1):peer does not do paranoid keepalives.

.Feb 29 14:36:24.547: ISAKMP:(0:5:SW:1):deleting SA reason "BY user command" state (R) QM_IDLE       (peer 95.140.92.16)
.Feb 29 14:36:24.547: ISAKMP:(0:5:SW:1):deleting node 1280949153 error FALSE reason "Informational (in) state 1"
.Feb 29 14:36:24.551: ISAKMP: Unlocking IPSEC struct 0x82CBDB24 from delete_siblings, count 0
.Feb 29 14:36:24.555: ISAKMP: set new node -633138757 to QM_IDLE
.Feb 29 14:36:24.559: ISAKMP:(0:5:SW:1): sending packet to 95.140.92.16 my_port 4500 peer_port 12435 (R) QM_IDLE
.Feb 29 14:36:24.559: ISAKMP:(0:5:SW:1):purging node -633138757
.Feb 29 14:36:24.563: ISAKMP:(0:5:SW:1):Input = IKE_MESG_INTERNAL, IKE_PHASE1_DEL
.Feb 29 14:36:24.563: ISAKMP:(0:5:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_DEST_SA

.Feb 29 14:36:24.563: ISAKMP:(0:5:SW:1):deleting SA reason "No reason" state (R) QM_IDLE       (peer 95.140.92.16)
.Feb 29 14:36:24.563: ISAKMP (0:134217733): returning address 172.16.251.46 to pool
.Feb 29 14:36:24.567: ISAKMP: Unlocking IKE struct 0x82CBDB24 for isadb_mark_sa_deleted(), count 0
.Feb 29 14:36:24.567: ISAKMP: returning address 172.16.251.46 to pool
.Feb 29 14:36:24.567: ISAKMP: Deleting peer node by peer_reap for 95.140.92.16: 82CBDB24
.Feb 29 14:36:24.567: ISAKMP: returning address 172.16.251.46 to pool
.Feb 29 14:36:24.571: ISAKMP:(0:5:SW:1):deleting node 1838299249 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.571: ISAKMP:(0:5:SW:1):deleting node 2127426640 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.571: ISAKMP:(0:5:SW:1):deleting node -714518789 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.571: ISAKMP:(0:5:SW:1):deleting node -1152363143 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.575: ISAKMP:(0:5:SW:1):deleting node 1488608236 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.575: ISAKMP:(0:5:SW:1):deleting node -1399061497 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.575: ISAKMP:(0:5:SW:1):deleting node 1619324510 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.575: ISAKMP:(0:5:SW:1):deleting node -1118440403 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.575: ISAKMP:(0:5:SW:1):deleting node 478458228 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.575: ISAKMP:(0:5:SW:1):deleting node -552724267 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.575: ISAKMP:(0:5:SW:1):deleting node 466751117 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.579: ISAKMP:(0:5:SW:1):deleting node 1873201770 error FALSE reason "IKE deleted"
.Feb 29 14:36:24.579: ISAKMP:(0:5:SW:1):deleting node 1280949153 error FALSE reason "IKE deleted"