Accessing running nodes
=======================

Within the mesh network all Nodes have IPv6 addresses and are treated like regular
computers - with a built-in WLAN device. Once we know the IPv6 address, one can
access the device - to initiate a firmware update, perform various sorts of maintenance
for customized setups, or to just look what is going on when a node does not perform
as expected.

**Access** may mean a mere ``ping``/``traceroute`` to determine if a host can be reached.
To truly enter a machine, one will use SSH. See :doc:`/user/authentication` for information
how to set it up.

How to find the IPv6 address of a desired node
----------------------------------------------

The IPv6 addresses of the nodes are static and derived from the MAC addresses.
Consequently, one needs to determine the IPv6 address only once per device.

To find the IPv6 address one can:

    * Look at the bottom of the device and find the MAC address there.
    * Directly connect via LAN-Cable and use the **next_node** addresses (if configured).
    *
        There are rules for an automated transcription of MAC addresses into IPv6
        addresses.
        You can find one implementation with some description at `ben.akrin.com <http://ben.akrin.com/?p=1347>`_.

        The procedure is basically an insertion of ``ff:ef`` in the middle, some bit
        swapping and adding ``fe80::`` as prefix.
    *
        You can find a node address if you know the IPv4 address of a client connected
        to it. If you perform a ``batctl traceroute`` to that client from any other Node
        in the mesh, the MAC address can be found in the last hub::

            $ batctl traceroute 10.135.17.193

            traceroute to 10.135.17.193 (26:a4:3c:f0:b5:0a), 50 hops max, 20 byte packets
            1: 12:fe:ed:3b:3f:cb  22.418 ms  23.008 ms  24.980 ms
            2: 26:a4:3c:f0:b5:0a  28.733 ms  26.018 ms  22.403 ms
    *
        Check response times - the nodes answering first are those connected directly
        to the querying host::

            $ ping6 -I bat0 ff02::2 | head -n 5

            PING ff02::2(ff02::2) from fe80::ec88:71ff:fefa:40cc bat0: 56 data bytes
            64 bytes from fe80::ec88:71ff:fefa:40cc: icmp_seq=1 ttl=64 time=0.066 ms
            64 bytes from fe80::c24a:ff:fe42:2120: icmp_seq=1 ttl=255 time=26.6 ms (DUP!)
            64 bytes from fe80::fa1a:67ff:fe31:69ca: icmp_seq=1 ttl=255 time=27.1 ms (DUP!)
            64 bytes from fe80::12fe:edff:feaf:57cc: icmp_seq=1 ttl=255 time=27.5 ms (DUP!)

        These addresses are local-link IPv6 addresses and can be contacted directly.

.. note::
        WLAN and Ethernet are different devices, each with it's own MAC address.

        It is expected that these MAC addresses are not always exactly the same as
        the ones seen underneath the device. Only one of either devices is depicted.

Contacting the device
---------------------

For a mere ping, perform::

    $ ping6 -I bat0 fe80::12fe:edff:feaf:57cc

    PING fe80::12fe:edff:feaf:57cc(fe80::12fe:edff:feaf:57cc) from fe80::ec88:71ff:fefa:40cc bat0: 56 data bytes
    64 bytes from fe80::12fe:edff:feaf:57cc: icmp_seq=1 ttl=64 time=54.2 ms
    64 bytes from fe80::12fe:edff:feaf:57cc: icmp_seq=2 ttl=64 time=28.3 ms

i.e. use ping6 instead of IPv4 ping and help with the interface.

For SSH, analogously do::

      $ ssh fe80::12fe:edff:feaf:57cc%bat0

      The authenticity of host 'fe80::12fe:edff:feaf:57cc%bat0 (fe80::12fe:edff:feaf:57cc%bat0)' can't be established.
      RSA key fingerprint is 53:5c:ac:f8:65:74:0b:cb:a4:67:26:3a:f5:65:2f:77.
      Are you sure you want to continue connecting (yes/no)?