IPv6 default routes timing out?

IPv6 default routes timing out?

[Roland Dreier]

I recently set up IPv6 on home home network -- openbsd 4.5 box serving
as a router with wired and wireless ports, advertising routes via the
openbsd rtadvd daemon.  I have no problem on boxes on the wired
network, which gets a default route like:

    default via fe80::240:63ff:feda:3d15 dev eth0  proto kernel  metric 1024  expires 8630sec mtu 1500 advmss 1440 hoplimit 64

However on laptops on the wireless network, I've seen the route
timeout and apparently never reappear.  This happens running both old
kernels like 2.6.24 and also with 2.6.31-rc4, and on systems with both
ipw2200 and iwlagn wirelss.  The symptom is that if I leave my laptop
running, say, overnight, in the morning the ipv6 default route is
gone.  ipv4 networking still works fine, and if I try explicit
link-local ipv6 addresses on the laptop, they work fine too.  But the
ipv6 internet is gone because the kernel has no idea how to route
packets to it.

The openbsd rtadvd config is pretty basic, just:

    ral0:\  
            :addr="2001:470:8379:2::":prefixlen#64:rltime#9000:\
            :maxinterval#120:mininterval#60:

Any ideas as to what I'm doing wrong, or where the problem might be?

Thanks,
  Roland

Re: IPv6 default routes timing out?

[John Dykstra]

On Wed, 2009-07-29 at 10:42 -0700, Roland Dreier wrote:
> I recently set up IPv6 on home home network -- openbsd 4.5 box serving
> as a router with wired and wireless ports, advertising routes via the
> openbsd rtadvd daemon.  I have no problem on boxes on the wired
> network, which gets a default route like:
> 
>     default via fe80::240:63ff:feda:3d15 dev eth0  proto kernel  metric 1024  expires 8630sec mtu 1500 advmss 1440 hoplimit 64
> 
> However on laptops on the wireless network, I've seen the route
> timeout and apparently never reappear.  This happens running both old
> kernels like 2.6.24 and also with 2.6.31-rc4, and on systems with both
> ipw2200 and iwlagn wirelss.  The symptom is that if I leave my laptop
> running, say, overnight, in the morning the ipv6 default route is
> gone.  ipv4 networking still works fine, and if I try explicit
> link-local ipv6 addresses on the laptop, they work fine too.  But the
> ipv6 internet is gone because the kernel has no idea how to route
> packets to it.
> 
> The openbsd rtadvd config is pretty basic, just:
> 
>     ral0:\  
>             :addr="2001:470:8379:2::":prefixlen#64:rltime#9000:\
>             :maxinterval#120:mininterval#60:
> 
> Any ideas as to what I'm doing wrong, or where the problem might be?

First thing I'd do is leave wireshark running overnight on the laptop
and see if the multicast router ads are making it to there.
--
John

Re: IPv6 default routes timing out?

[Roland Dreier]

 > First thing I'd do is leave wireshark running overnight on the laptop
 > and see if the multicast router ads are making it to there.

Thanks, I did some more debugging it seems the issue is in the
router's (openbsd) wireless driver -- it thinks it is broadcasting
router advertisements but they aren't making it to the laptop.

So everything seems OK on the Linux side.

 - R.

Re: IPv6 default routes timing out?

[John Dykstra]

On Thu, 2009-07-30 at 09:58 -0700, Roland Dreier wrote:
> Thanks, I did some more debugging it seems the issue is in the
> router's (openbsd) wireless driver -- it thinks it is broadcasting
> router advertisements but they aren't making it to the laptop.

Could it be that there's something buggy in the laptop wireless driver
or hardware re filtering of multicast packets at the L2 level? 

  --  John

Re: IPv6 default routes timing out?

[Roland Dreier]

 > > Thanks, I did some more debugging it seems the issue is in the
 > > router's (openbsd) wireless driver -- it thinks it is broadcasting
 > > router advertisements but they aren't making it to the laptop.

 > Could it be that there's something buggy in the laptop wireless driver
 > or hardware re filtering of multicast packets at the L2 level? 

Well, I see router advertisements (and pings to ff02::1) from the router
on both of the two laptops I have handy, and then after a while the
openbsd system seems to stop broadcasting -- I no longer see the
broadcast ipv6 packets on either laptop, but if I just do "ifconfig ral0
down; ifconfig ral0 up" on the openbsd system then everything seems to
come back.  So it seems unlikely that the problem is anywhere except on
the openbsd system sending.

It's interesting to note that the only broadcasts that the openbsd
router is going to send that matter in my setup are ipv6 router
advertisements -- before I started using ipv4, all the broadcasts would
have been arps from the laptops to the router, so I would have never
noticed that the router stopped being able to broadcast.

 - R.

Re: IPv6 default routes timing out?

[John Dykstra]

On Thu, 2009-07-30 at 11:34 -0700, Roland Dreier wrote:
> Well, I see router advertisements (and pings to ff02::1) from the router
> on both of the two laptops I have handy, and then after a while the
> openbsd system seems to stop broadcasting -- I no longer see the
> broadcast ipv6 packets on either laptop, but if I just do "ifconfig ral0
> down; ifconfig ral0 up" on the openbsd system then everything seems to
> come back.

Note that these are actually multicasts, not broadcasts.  There's not
much difference on the sending end, but on the receiving end there's
usually filtering at the NIC level that doesn't apply to broadcasts.

That's why I'm a little bit suspicious of the laptop end of your
connection.  It's not uncommon for multicast to be broken in various
ways without people noticing, because they don't use it very much on
IPv4.  However, it's fundamental to IPv6.

  --  John 

Re: IPv6 default routes timing out?

[Roland Dreier]

 > Note that these are actually multicasts, not broadcasts.  There's not
 > much difference on the sending end, but on the receiving end there's
 > usually filtering at the NIC level that doesn't apply to broadcasts.
 > 
 > That's why I'm a little bit suspicious of the laptop end of your
 > connection.  It's not uncommon for multicast to be broken in various
 > ways without people noticing, because they don't use it very much on
 > IPv4.  However, it's fundamental to IPv6.

Fair enough ... however, given that two independent laptops (using two
different wireless drivers / kernel versions) stop getting the router
advertisements (which are, as you said, multicast to the all nodes
address, not truly broadcast) at the same time, and given that
bouncing the driver on the sender (openbsd router) fixes things, I'm
much more likely to blame the sender in this case.