A Note on SIT Tunnel at Home

This blog article records the progress of setting up IPv6 tunnel to Hurricane Electric at home where my ISP has no plan in sight to provide prefix-delegated IPv6 access over a PPPoE.

Shorthands and Assumptions in This Note

  • eth0 connects to the Internet via IPv4. This note shall also apply to encapsulated interfaces, e.g. vlan15@eth0, lte0 or pppoe0.
  • eth1 connects to local LAN. Similar as above, the process shall be the same when LAN side is a VLAN or bridge (or both).
  • tun0 denotes the sit tunnel interface created in this step.
  • A line beginning with # denotes comments in the configuration notes.

Setting up the Tunnel Interface on ER-X

If registered correctly on TunnelBroker, it should provide the following information:

  • Logical address at local endpoint, e.g. 2001:444:111:222::2/64
  • Logical address at remote endpoint, e.g. 2001:444:111:222::1/64
  • IPv4 address at remote endpoint where encapsulated traffic is sent, e.g., the HE tunneling endpoint in Paris.
  • A routable prefix for client side delegation, e.g. 2001:444:112:222::/64. This is usually different from the v6 addresses for the endpoint, and HE will show segments of the prefix in bold.

Now fill ER-X configuration nodes with corresponding information and default routing for IPv6:

            address: [Fill logical v6 address in CIDR at endpoint]
            description: [Give a name to this tun]
            encapsulation: sit
            local-ip: [Fill in IPv4 address at eth0]
            remote-ip: [Fill in IPv4 address at tunneling endpoint]
                next-hop-interface: tun0
            # This creates a default IPv6 routing table entry that
            # routes all non-link-local address to the tunnel.

At this point, one should be able to ping any IPv6 address from the ER-X. If this is working, continue to instruct the LAN interface to delegate the prefix

            dup-addr-detect-transmits: 1
            # Stateless SLAAC configuration might produce identical
            # IP addresses. This allow the network to detect whether
            # a stateless address already exists.
                # Set autoconf to allow stateless delegation by SLAAC
                    [Fill routable delegated prefix here]:
                        autonomous-flag: true
                        # Instructs computers on this network to auto
                        # discover DNS servers
                        on-link-flag: true
                        # Indicates that this prefix exists on the
                        # same Ethernet link, i.e. these addresses
                        # does not require routing

IPv6 enabled devices shall now receive globally unique IPv6 address assigned via SLAAC and prefix delegation.

Subsequent Steps

  • Confirm IPv6 assignment on LAN devices
$ ip addr
2: eno1:  mtu 1480 qdisc fq_codel state UP group default qlen 1000
     link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
     inet brd scope global dynamic noprefixroute eno1
        valid_lft 80444sec preferred_lft 80444sec
     inet6 2001:470:d:XXXX:XXXX:XXXX:XXXX:dfd3/64 scope global dynamic noprefixroute 
        valid_lft 2591976sec preferred_lft 86376sec
     inet6 fe80::be40:XXXX:XXXX:XXXX/64 scope link noprefixroute 
        valid_lft forever preferred_lft forever
  • Trace IPv6 connections to an IPv6 enabled website
$ traceroute -6 ac.cth451.me -n
 traceroute to ac.cth451.me (2606:4700:30::681c:1b16), 30 hops max, 80 byte packets
  1  2001:470:d:XXXX:XXXX:XXXX:XXXX:XXXX  0.415 ms  0.533 ms  0.624 ms
  2  2001:470:c:XXXX::1  185.353 ms *  203.802 ms
  3  2001:470:0:9d::1  178.603 ms  167.001 ms  189.255 ms
  4  2001:504:0:3:0:1:3335:1  196.520 ms  179.737 ms  196.117 ms
  5  2400:cb00:12:1024::6ca2:d61d  185.036 ms 2400:cb00:12:1024::6ca2:d614  175.573 ms 2400:cb00:12:1024::6ca2:d608  185.263 ms
  • It is advisable to setup network wide firewall on the router, as addresses can be reached by any other IPv6 connected devices from the Internet.

Further Notes

  • The sit tunnel shall also work if setup correctly on any other router or even a personal computer with public IPv4 address. I am unable to replicate the settings on a Linux router via raw commands as I do not own a linux machine with public IPv4 address.
  • I am not sure if the method would work if the local endpoint is behind NAT. This scenario will be experimented on after I return to campus.