traceroute6 issue behind NAT66 on CentOS

[yzyuestc]

Hello, everyone. I meet a strange traceroute problem when using traceroute6 behind nat66. I have two servers, one is in HK, the other is in Frankfurt. And two servers use HE's tunnel broker in different places.The topology likes below:

HE's Tunnel in DE                         HE's Tunnel in HK
        |  fra-he                                 |    tb0
-----------------     VPN Connection     -----------------
| Frankfurt (A)   | -------------------  |   Hong Kong (B) |
----------------- tun1             tun4  -----------------
                                     
The server in Frankfurt (A) has a range of IPv6: 2001:470:7429::/48, the server in Hong Kong (B) has a range of  IPv6 : 2001:470:fadc::/48
And I compiled the kernel of server A to support IPv6 nat.
I need to route 2001:620::/32 via server A to Internet, and I applied ip6tables NETMAP rules on server A:
ip6tables -t nat -A POSTROUTING -s 2001:470:fadc::/48 -o fra-he -j NETMAP 2001:470:7429::/48
ip6tables -t filter -A IPUT -i tun1 -j ACCEPT
ip6tables -t filter -A FORWARD -i tun1 -o fra-de -j ACCEPT
ip6tables -t filter -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
Then I added  route tables in the file /etc/iproute2/rt_tables and add some ip rules to 2 servers respectively.
I ping from server B :ping6 2001:620:130:a080::46, everything goes smoothly. The traffic was routed to server A, and server A did a address translation:
> ping6 strongswan.org
> PING strongswan.org(2001:620:130:a080::46) 56 data bytes
> 64 bytes from 2001:620:130:a080::46: icmp_seq=1 ttl=55 time=289 ms
> 64 bytes from 2001:620:130:a080::46: icmp_seq=2 ttl=55 time=288 ms
> 64 bytes from 2001:620:130:a080::46: icmp_seq=3 ttl=55 time=283 ms
> 64 bytes from 2001:620:130:a080::46: icmp_seq=4 ttl=55 time=284 ms
> 64 bytes from 2001:620:130:a080::46: icmp_seq=5 ttl=55 time=282 ms
> 64 bytes from 2001:620:130:a080::46: icmp_seq=6 ttl=55 time=282 ms
But server B traceroute6 works no good:
traceroute6  2001:620:130:a080::46
> traceroute to 2001:620:130:a080::46 (2001:620:130:a080::46), 30 hops max, 80 > byte packets
> 1  transit-hkg1-fra.homehosts.net (2001:470:fadc:6604::2)  266.003 ms  265.993 ms  265.999 ms
> 2  * * *
> 3  * * *
> 4  * * *
> 5  * * *
> 6  * * *
> 7  * * *
It's strange that I can traceroute from server A :o
traceroute6 2001:620:130:a080::46
> traceroute to 2001:620:130:a080::46 (2001:620:130:a080::46), 30 hops max, 80 byte packets
> 1  yzyuestc2-4.tunnel.tserv6.fra1.ipv6.he.net (2001:470:1f0a:d1e::1)  5.697 ms  5.632 ms  5.622 ms
> 2  v399.core1.fra1.he.net (2001:470:0:69::1)  7.655 ms  7.887 ms  7.880 ms
> 3  100ge3-1.core1.ams1.he.net (2001:470:0:2d4::1)  7.193 ms  11.531 ms  7.177 ms
> 4  swiCE3-10GE-4-1.switch.ch (2001:7f8:1::a500:559:1)  107.881 ms  107.875 ms  107.867 ms
> 5  swiGE2-10GE-3-1.switch.ch (2001:620:0:c093::2)  23.088 ms  17.289 ms  17.348 ms
> 6  swiEL2-10GE-3-1.switch.ch (2001:620:0:c094::2)  24.190 ms  17.894 ms  17.746 ms
> 7  swiLS2-10GE-1-2.switch.ch (2001:620:0:c00c::2)  17.084 ms  17.420 ms  17.398 ms
> 8  swiEZ1-10GE-2-7.switch.ch (2001:620:0:c03c::2)  81.610 ms  81.324 ms  81.304 ms
> 9  swiRA2-10GE-0-0-2-0.switch.ch (2001:620:0:c058::2)  18.913 ms  19.011 ms  18.948 ms
> 10  2001:620:0:ffc8::2 (2001:620:0:ffc8::2)  19.613 ms  21.479 ms  21.248 ms
> 11  * * *
> 12  * * *
I am sure that I added table to every interfaces to spilt routing. I checked the routing tables and found no mistakes.
Anyone help? Thanks !