Tunnel opened but not traffic allowed (or so)

[ljonget]

Hi all,

I'm using HE tunnelbroker since 2016 without issue, and since 1 month or so, it stopped working.
Since then, the linux box (a Synology NAS) has been updated, the ISP router might have been updated as well (don't know and can't know...) so it's difficult to know why.

here is more info :
- the setup is : a synology NAS with a private IPV4 address and the ISP router with a static public IPV4 address
- all commands (scripted, so they didn't changed) to bring the interface up with ips,... are successful
- ping to server IPV4 address is OK
- ping to client IPV6 address is OK
- ping to server IPV4 address is OK
- when running a IPv6 Portscan from tunnelbroker.net website, the results are OK and ports that should be opened are opened
- ping to a IPV6 website (like www.kame.net, ...) is sometime ok sometime not ok and might depend on packets size
- curl to a IPV6 fails anytime.

what I've tried :
- setup the IPV6 on another Linux box (a VM on my laptop) : same behavior
- delete tunnel and create a new one : same
- tcpdump the IPV6 traffic while pinging and curling : seeing a lot of output packet but only a few for echo request, and none for http(s) calls and so a lot of retransmission

it seems tunnel is OK, and that router is forwarding IP protocol 41 as the portscan is ok, but can't understand why outgoing traffic (except ping) is failing...

Any ideas ?
what else can I do to narrow down culprit ?

thanks a lot

[cholzhauer]

You said it seems to depend on packet size...can you just set the MTU to a value that works and leave it?

[ljonget]

Yes, I said "it might" as when a ping with default packet size (=56) and it works, it still works if increase the packet size to 100, then 500 then 1000 it works, and a few seconds after it doesn't anymore, even with default value.

if I let run the ping command, I have a huge loss of packet :

Code Select Expand

PING 2001:200:dff:fff1:216:3eff:feb1:44d7(2001:200:dff:fff1:216:3eff:feb1:44d7) 56 data bytes
64 bytes from 2001:200:dff:fff1:216:3eff:feb1:44d7: icmp_seq=12 ttl=50 time=319 ms
64 bytes from 2001:200:dff:fff1:216:3eff:feb1:44d7: icmp_seq=13 ttl=50 time=320 ms
64 bytes from 2001:200:dff:fff1:216:3eff:feb1:44d7: icmp_seq=14 ttl=50 time=321 ms
64 bytes from 2001:200:dff:fff1:216:3eff:feb1:44d7: icmp_seq=15 ttl=50 time=318 ms
^C
--- 2001:200:dff:fff1:216:3eff:feb1:44d7 ping statistics ---
73 packets transmitted, 4 received, 94% packet loss, time 72006ms
rtt min/avg/max/mdev = 318.390/320.028/321.046/1.240 ms


I tried to set MTU to 1480 (default value in tunnel broker account) and to minimum (1280).