problem with ipv6 behind router

[NNdroid]

After the ipv6 packet passes through the router (one more hop), there is a problem!
pc1 <---> switch <---> pc2
When I connect 2 devices directly, ipv4 and ipv6 tcp works fine after adding route on the other device.
pc1 <---> router <---> switch <---> pc2
But when I add a router between these two devices, the situation is completely different. The tcp handshake cannot be completed under ipv6, but ipv4 can (guessing that there should be nat so it can), and the tcpdump capture output is as follows:

pc2 tcpdump output:
1 0.000000 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241244475 TSecr=0 WS=128
2 0.000816 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 94 80 → 58720 [SYN, ACK] Seq=0 Ack=1 Win=28800 Len=0 MSS=1440 SACK_PERM TSval=3974596627 TSecr=4241244475 WS=128
4 1.043100 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241245519 TSecr=0 WS=128
3 1.001259 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 94 [TCP Retransmission] 80 → 58720 [SYN, ACK] Seq=0 Ack=1 Win=28800 Len=0 MSS=1440 SACK_PERM TSval=3974596627 TSecr=4241244475 WS=128
6 3.002627 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 94 [TCP Retransmission] 80 → 58720 [SYN, ACK] Seq=0 Ack=1 Win=28800 Len=0 MSS=1440 SACK_PERM TSval=3974596627 TSecr=4241244475 WS=128
5 1.043649 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 2#1] 80 → 58720 [ACK] Seq=1 Ack=1 Win=3686400 Len=0 TSval=3974597670 TSecr=4241244475
7 3.123047 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241247599 TSecr=0 WS=128
9 7.003012 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 94 [TCP Retransmission] 80 → 58720 [SYN, ACK] Seq=0 Ack=1 Win=28800 Len=0 MSS=1440 SACK_PERM TSval=3974596627 TSecr=4241244475 WS=128
8 3.123521 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 2#2] 80 → 58720 [ACK] Seq=1 Ack=1 Win=3686400 Len=0 TSval=3974599750 TSecr=4241244475
10 7.203106 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241251679 TSecr=0 WS=128
11 7.203566 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 2#3] 80 → 58720 [ACK] Seq=1 Ack=1 Win=3686400 Len=0 TSval=3974603830 TSecr=4241244475
12 15.003939 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 94 [TCP Retransmission] 80 → 58720 [SYN, ACK] Seq=0 Ack=1 Win=28800 Len=0 MSS=1440 SACK_PERM TSval=3974596627 TSecr=4241244475 WS=128
13 15.363116 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241259839 TSecr=0 WS=128
14 15.363560 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 2#4] 80 → 58720 [ACK] Seq=1 Ack=1 Win=3686400 Len=0 TSval=3974611990 TSecr=4241244475
15 31.004732 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 94 [TCP Retransmission] 80 → 58720 [SYN, ACK] Seq=0 Ack=1 Win=28800 Len=0 MSS=1440 SACK_PERM TSval=3974596627 TSecr=4241244475 WS=128
16 32.003277 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241276479 TSecr=0 WS=128
17 32.003909 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 2#5] 80 → 58720 [ACK] Seq=1 Ack=1 Win=3686400 Len=0 TSval=3974628630 TSecr=4241244475

router tcpdump output:
1 0.000000 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241244475 TSecr=0 WS=128
2 1.043086 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241245519 TSecr=0 WS=128
3 1.044179 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 80 → 58720 [ACK] Seq=1 Ack=1 Win=28800 Len=0 TSval=3974597670 TSecr=4241244475
4 3.123041 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241247599 TSecr=0 WS=128
5 3.124042 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 3#1] 80 → 58720 [ACK] Seq=1 Ack=1 Win=28800 Len=0 TSval=3974599750 TSecr=4241244475
6 7.203083 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241251679 TSecr=0 WS=128
7 7.204086 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 3#2] 80 → 58720 [ACK] Seq=1 Ack=1 Win=28800 Len=0 TSval=3974603830 TSecr=4241244475
8 15.363116 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241259839 TSecr=0 WS=128
9 15.364046 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 3#3] 80 → 58720 [ACK] Seq=1 Ack=1 Win=28800 Len=0 TSval=3974611990 TSecr=4241244475
10 32.003225 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241276479 TSecr=0 WS=128
11 32.004429 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 3#4] 80 → 58720 [ACK] Seq=1 Ack=1 Win=28800 Len=0 TSval=3974628630 TSecr=4241244475

pc1 tcpdump output:
1 0.000000 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241244475 TSecr=0 WS=128
2 1.043056 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241245519 TSecr=0 WS=128
3 1.045290 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 80 → 58720 [ACK] Seq=1 Ack=1 Win=28800 Len=0 TSval=3974597670 TSecr=4241244475
4 3.123056 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241247599 TSecr=0 WS=128
5 3.125104 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 3#1] 80 → 58720 [ACK] Seq=1 Ack=1 Win=28800 Len=0 TSval=3974599750 TSecr=4241244475
6 7.203074 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241251679 TSecr=0 WS=128
7 7.205131 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 3#2] 80 → 58720 [ACK] Seq=1 Ack=1 Win=28800 Len=0 TSval=3974603830 TSecr=4241244475
8 15.363043 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241259839 TSecr=0 WS=128
9 15.365048 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 3#3] 80 → 58720 [ACK] Seq=1 Ack=1 Win=28800 Len=0 TSval=3974611990 TSecr=4241244475
10 32.003055 2001:b000:168:12f3::cafe:2019 2001:4838:0:1b::201 TCP 94 [TCP Retransmission] 58720 → 80 [SYN] Seq=0 Win=64440 Len=0 MSS=1432 SACK_PERM TSval=4241276479 TSecr=0 WS=128
11 32.005329 2001:4838:0:1b::201 2001:b000:168:12f3::cafe:2019 TCP 86 [TCP Dup ACK 3#4] 80 → 58720 [ACK] Seq=1 Ack=1 Win=28800 Len=0 TSval=3974628630 TSecr=4241244475

It can be seen that the packets captured on pc1 and router are exactly the same
Can anyone help me? thank you very much

[NNdroid]

it is work fine.