ipip(4) - NetBSD Manual Pages

IPIP(4)                   NetBSD Programmer's Manual                   IPIP(4)


NAME

     ipip - encapsulating network device


SYNOPSIS

     pseudo-device ipip [count]


DESCRIPTION

     The ipip network interface is a pseudo device that allows to encapsulate
     datagrams into IP. These encapsulated datagrams are routed to a destina-
     tion host, where they are decapsulated and further routed to their final
     destination.  The so called ``tunnel'' appears to the inner datagrams
     like one hop.  Encapsulation is according to RFC 2003. The outer datagram
     header is of IP type 4 (IPIP).

     The network interfaces are named ipip0, ipip1 and so on, as many as have
     given on the pseudo-device line in the system config file.

     Note that the IP addresses of the tunnel endpoints may be the same as the
     ones defined with ifconfig for the interface (as if IP is encapsulated),
     but need not be.


EXAMPLE

     Configuration example:

     Host X-- Host A  ----------------tunnel---------- cisco D------Host E
               \                                          |
                \                                        /
                  +------Host B----------Host C----------+

        On host A (NetBSD):

        # route add default B
        # ifconfig ipipN  A D netmask 0xffffffff  up
        # route add E D

        On Host D (Cisco):

        Interface TunnelX
         ip unnumbered D   ! e.g. address from Ethernet interface
         tunnel source D   ! e.g. address from Ethernet interface
         tunnel destination A
        ip route C <some interface and mask>
        ip route A mask C
        ip route X mask tunnelX

        OR

        On Host D (NetBSD):

        # route add default C
        # ifconfig ipipN D A

     If all goes well, you should see packets flowing ;-)

     If you want to reach Host A over the tunnel (from the Cisco D), then you
     have to have an alias on Host A for e.g. the Ethernet interface like:
          ifconfig <etherif> alias Y
      and on the cisco
          ip route Y mask tunnelX


NOTE

     For correct operation, the ipip device needs a route to the destination,
     that is less specific than the one over the tunnel.  (Basically, there
     needs to be a route to the decapsulating host that does not run over the
     tunnel, as this would be a loop ..)

     In order to ifconfig to actually mark the interface as up, the keyword
     ``up'' must be given last on its command line.

     The kernel must be set to forward datagrams by either option ``GATEWAY''
     in the kernel config file or by issuing the appropriate option to sysctl.


SEE ALSO

     netintro(4), ip(4), gre(4), atalk(4), inet(4), ifconfig(8), options(4),
     protocols(5), sysctl(8)

     A description of IPIP encapsulation can be found in RFC 2003.


BUGS

     The ipip_compute_route() code in ip_ipip.c toggles the last bit of the
     IP-address to provoke the search for a less specific route than the one
     directly over the tunnel to prevent loops. This is possibly not the best
     solution.

     Traceroute does not work yet over the tunnel :(

NetBSD 1.5.3                     28 March 1999                               2