I am trying to setup a sit tunnel between an Ubuntu server and a Mikrotik router.
I setup the local and remote IPv4 addresses on each device and setup the IPv6 addresses at either end of the tunnel.
I am however unable to ping the IPv6 addresses across the tunnel - from either end. I can successfully ping the IPv6 address at the local end of the tunnel from both sides.
I decided to try and do a tcpdump on the Ubuntu side of the link to try and determine if my ISP was filtering packets.
All the Protocol-41 packets were arriving but with the wrong source IP. The source IP was set on the router as xx.xx.78.85 but the packets were arriving with an IP of xx.xx.78.86. The server did not recognise the IP and was discarding the packets.
Similarly - pings from the server side were arriving on the router but not being responded to.