IPv6 + tun

IPv6 + tun

Post by nitsu » Thu, 06 Jul 2000 04:00:00

Hello, I upgraded to 2.7 a few days ago and I see this message
whenever user-ppp is invoked:   tun0: not multicast capable, IPv6 not
enabled. Now out of curiosity, I searched the maillist archives and
found to posts that had suggested this problem occurs when IPv6
support is not enabled in the kernel, but I have "option INET6" in my
configure file and my two nics have been assigned IPv6 addresses.
The tun0 interface works fine with IPv4. What is the solution to this?
Does IPv6 need multicast support? The tun interface seems to only have
two modes, broadcast and pointopoint. Does tun have a multicast mode?

1. IPv6, TUN, routing


I've got a problem configuring a computer as a border router for a TUN
device.  The program for the TUN device logs packets/pings correctly
on the local host, but doing the same in the network doesn't work at
all.  Basically the TUN device will act as an endpoint for another
network and (at the moment) doesn't perform any work except forwarding

I've got two machines: machine A, which runs router advertisements with
radvd (and the program for the TUN device (with prefix fec0::/64)), and
machine B as a test machine.  Forwarding is enabled.

Both test computers have link-local addresses (fe80::.../64) and can
ping each other under those addresses (while providing ping6 with an
interface name).  The ::/0 entry is sent to "lo", so other (IPv6) hosts
and the internet (e.g. ipv6.google.com) aren't reachable through it.

Machine A, when run with the TUN program, then has the routing entry:

fec0::/64       ::                         U    256  0     0  tun0

and this works, so (locally) pinging some address in that range appears
in the program.

Now, when I run radvd with the configuration file:

interface eth1 {
  AdvSendAdvert on;
  MinRtrAdvInterval 3;
  MaxRtrAdvInterval 10;
  AdvRouteLifetime 30;

  prefix fec0::/64 {
    AdvOnLink on;
    AdvAutonomous on;

, machine B gets two additional routing entries:

fec0::/64       ::                         UAe    256   0     0  eth1
::/0            fe80::217:a4ff:fe1a:e3af   UGDAe  1024  0     1  eth1
                     ^-- Machine A

, which I assume are correct(?).

Now pinging some address in the fec0::/64 range doesn't work on machine
B, the packets just vanish with "Address unreachable"; on machine A,
using tcpdump, no packets come through.

I'd be very grateful for any hints and ideas to make this work (or why
this can't work for whatever reason).


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