IPV6 routing problem

IPV6 routing problem

[Sharat Masetty]

 I have an IPV6 routing problem that has only surfaced on a 3.10
kernel version. This problem is not seen on 3.4 kernel. I will keep
the problem statement as brief as possible.

I have two interfaces say eth0 and eth1. I have a host route to a
destination over eth1, but this route has a global gateway
address(via) of the router on the link. When this global gateway is
present in the route, the kernel does not seem to pick up the route,
but falls back to the default route which is eth0. When this gateway
is removed from the route or if the gateway is changed to a link local
address of the router, instead of the global address, then routing
seems to work as expected and kernel picks up interface eth1.

== does not work ==
<dest-addr> via <global scope -gateway addr>dev eth1 metric 1024
<global scope -gateway addr> dev eth1  metric 1024

I checked the git commits diff between 3.4 and 3.10 for ipv6/route.c
and ipv6/ip6_fib.c, but looks like they are close to an year apart
with lots of changes. Hence I wanted to reach out to you to see if any
recent changes in IPV6 routing is causing this difference in behavior.

Any help would be greatly appreciated.

Thanks
Sharat

Re: IPV6 routing problem

[Hannes Frederic Sowa]

Hi!

On Tue, Jan 21, 2014 at 06:41:58PM -0700, Sharat Masetty wrote:
>  I have an IPV6 routing problem that has only surfaced on a 3.10
> kernel version. This problem is not seen on 3.4 kernel. I will keep
> the problem statement as brief as possible.

Could you do me a favor and test this on a recent 3.13 kernel? Thanks!
Please also state the specific kernel version (I guess you use one).

> I have two interfaces say eth0 and eth1. I have a host route to a
> destination over eth1, but this route has a global gateway
> address(via) of the router on the link. When this global gateway is
> present in the route, the kernel does not seem to pick up the route,
> but falls back to the default route which is eth0. When this gateway
> is removed from the route or if the gateway is changed to a link local
> address of the router, instead of the global address, then routing
> seems to work as expected and kernel picks up interface eth1.
> 
> == does not work ==
> <dest-addr> via <global scope -gateway addr>dev eth1 metric 1024
> <global scope -gateway addr> dev eth1  metric 1024

Do you have CONFIG_IPV6_ROUTER_PREF activated?

> 
> I checked the git commits diff between 3.4 and 3.10 for ipv6/route.c
> and ipv6/ip6_fib.c, but looks like they are close to an year apart
> with lots of changes. Hence I wanted to reach out to you to see if any
> recent changes in IPV6 routing is causing this difference in behavior.

It should be a problem in ipv6/route.c, ip6_fib.c does not really care about
interfaces that much.

Thanks,

  Hannes

Re: IPV6 routing problem

[Hannes Frederic Sowa]

On Wed, Jan 22, 2014 at 08:07:59AM +0100, Hannes Frederic Sowa wrote:
> Hi!
> 
> On Tue, Jan 21, 2014 at 06:41:58PM -0700, Sharat Masetty wrote:
> >  I have an IPV6 routing problem that has only surfaced on a 3.10
> > kernel version. This problem is not seen on 3.4 kernel. I will keep
> > the problem statement as brief as possible.
> 
> Could you do me a favor and test this on a recent 3.13 kernel? Thanks!
> Please also state the specific kernel version (I guess you use one).

+stable.

A quick test worked for me. Maybe you could try with CONFIG_IPV6_ROUTER_PREF
enabled and one time with it disabled.

We should make this knob a runtime setting soon...

Thanks,

  Hannes

Re: IPV6 routing problem

[Sharat Masetty]

Unfortunately toggling this config setting CONFIG_IPV6_ROUTER_PREF did
not help, I see the same problem in both cases.
The kernel version I am using is 3.10.0.

Thanks for confirming that this is a non issue on 3.13 kernel version.
Would you happen to know which patch would have potentially fixed this
issue?


On Wed, Jan 22, 2014 at 12:11 AM, Hannes Frederic Sowa
<hannes@stressinduktion.org> wrote:
> On Wed, Jan 22, 2014 at 08:07:59AM +0100, Hannes Frederic Sowa wrote:
>> Hi!
>>
>> On Tue, Jan 21, 2014 at 06:41:58PM -0700, Sharat Masetty wrote:
>> >  I have an IPV6 routing problem that has only surfaced on a 3.10
>> > kernel version. This problem is not seen on 3.4 kernel. I will keep
>> > the problem statement as brief as possible.
>>
>> Could you do me a favor and test this on a recent 3.13 kernel? Thanks!
>> Please also state the specific kernel version (I guess you use one).
>
> +stable.
>
> A quick test worked for me. Maybe you could try with CONFIG_IPV6_ROUTER_PREF
> enabled and one time with it disabled.
>
> We should make this knob a runtime setting soon...
>
> Thanks,
>
>   Hannes
>

Re: IPV6 routing problem

[Emmanuel Thierry]

Hello,

Le 23 janv. 2014 à 08:15, Sharat Masetty a écrit :

> Unfortunately toggling this config setting CONFIG_IPV6_ROUTER_PREF did
> not help, I see the same problem in both cases.
> The kernel version I am using is 3.10.0.
> 
> Thanks for confirming that this is a non issue on 3.13 kernel version.
> Would you happen to know which patch would have potentially fixed this
> issue?

Your problem looks like the following one : 
http://marc.info/?l=linux-netdev&m=137280268407054&w=2

Which has been fixed in 3.10.4, and 3.11+

> On Wed, Jan 22, 2014 at 12:11 AM, Hannes Frederic Sowa
> <hannes@stressinduktion.org> wrote:
>> On Wed, Jan 22, 2014 at 08:07:59AM +0100, Hannes Frederic Sowa wrote:
>>> Hi!
>>> 
>>> On Tue, Jan 21, 2014 at 06:41:58PM -0700, Sharat Masetty wrote:
>>>> I have an IPV6 routing problem that has only surfaced on a 3.10
>>>> kernel version. This problem is not seen on 3.4 kernel. I will keep
>>>> the problem statement as brief as possible.
>>> 
>>> Could you do me a favor and test this on a recent 3.13 kernel? Thanks!
>>> Please also state the specific kernel version (I guess you use one).
>> 
>> +stable.
>> 
>> A quick test worked for me. Maybe you could try with CONFIG_IPV6_ROUTER_PREF
>> enabled and one time with it disabled.
>> 
>> We should make this knob a runtime setting soon...
>> 
>> Thanks,
>> 
>>  Hannes

Best regards.
Emmanuel Thierry

Re: IPV6 routing problem

[Hannes Frederic Sowa]

On Fri, Jan 24, 2014 at 10:36:54AM +0100, Emmanuel Thierry wrote:
> Hello,
> 
> Le 23 janv. 2014 à 08:15, Sharat Masetty a écrit :
> 
> > Unfortunately toggling this config setting CONFIG_IPV6_ROUTER_PREF did
> > not help, I see the same problem in both cases.
> > The kernel version I am using is 3.10.0.
> > 
> > Thanks for confirming that this is a non issue on 3.13 kernel version.
> > Would you happen to know which patch would have potentially fixed this
> > issue?
> 
> Your problem looks like the following one : 
> http://marc.info/?l=linux-netdev&m=137280268407054&w=2
> 
> Which has been fixed in 3.10.4, and 3.11+

Yes, that could very well be the case. We resolve the gateway while
inserting the route (if not on-link), and it may not be available
because of missing probes or no traffic went to it, yet. Thanks for
looking after this, Emmanuel.

I really recommend using the stable kernels btw. instead of the vanialla
point zero releases.

Thanks,

  Hannes

Re: IPV6 routing problem

[Sharat Masetty]

Thank you Emmanuel and Hannes, I went through the thread and the
suggested fix and it definitely makes sense. I will apply the fix and
test it out.

A general question, Can you suggest a good reference documentation to
understand the Linux kernel IPV6 routing and neighboring subsystem
better? The O Reilly book does not have much about IPV6.

Thanks
Sharat

On Fri, Jan 24, 2014 at 6:59 AM, Hannes Frederic Sowa
<hannes@stressinduktion.org> wrote:
> On Fri, Jan 24, 2014 at 10:36:54AM +0100, Emmanuel Thierry wrote:
>> Hello,
>>
>> Le 23 janv. 2014 à 08:15, Sharat Masetty a écrit :
>>
>> > Unfortunately toggling this config setting CONFIG_IPV6_ROUTER_PREF did
>> > not help, I see the same problem in both cases.
>> > The kernel version I am using is 3.10.0.
>> >
>> > Thanks for confirming that this is a non issue on 3.13 kernel version.
>> > Would you happen to know which patch would have potentially fixed this
>> > issue?
>>
>> Your problem looks like the following one :
>> http://marc.info/?l=linux-netdev&m=137280268407054&w=2
>>
>> Which has been fixed in 3.10.4, and 3.11+
>
> Yes, that could very well be the case. We resolve the gateway while
> inserting the route (if not on-link), and it may not be available
> because of missing probes or no traffic went to it, yet. Thanks for
> looking after this, Emmanuel.
>
> I really recommend using the stable kernels btw. instead of the vanialla
> point zero releases.
>
> Thanks,
>
>   Hannes
>

Re: IPV6 routing problem

[Cong Wang]

On Fri, Jan 24, 2014 at 10:50 AM, Sharat Masetty <sharat04@gmail.com> wrote:
> A general question, Can you suggest a good reference documentation to
> understand the Linux kernel IPV6 routing and neighboring subsystem
> better? The O Reilly book does not have much about IPV6.

Rami Rosen is writing a book on Linux networking which covers IPv6
as well. You can also search on Internet for his slides on IPv6 too.

Re: IPV6 routing problem

[Rami Rosen]

Hi,

A shameless plug - the book is already published:

http://www.apress.com/9781430261964

And the slides are available in
"IPv6 in the Linux Kernel", under
http://ramirose.wix.com/ramirosen


Rami Rosen

On Fri, Jan 24, 2014 at 10:05 PM, Cong Wang <cwang@twopensource.com> wrote:
> On Fri, Jan 24, 2014 at 10:50 AM, Sharat Masetty <sharat04@gmail.com> wrote:
>> A general question, Can you suggest a good reference documentation to
>> understand the Linux kernel IPV6 routing and neighboring subsystem
>> better? The O Reilly book does not have much about IPV6.
>
> Rami Rosen is writing a book on Linux networking which covers IPv6
> as well. You can also search on Internet for his slides on IPv6 too.
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