[libnice] Issues with candidate selection through wrong network interface

Juan Navarro juan.navarro at gmx.es
Tue Aug 29 15:28:59 UTC 2017

Thanks for the pointer!

it happened that I was just reading the commit logs when your email 
arrived, and reading the additions of commit b4abda09, where the 
compilation option "--with-ignored-network-interface-prefix" was 
introduced. I don't really understand how this change was able to 
improve my situation with the "docker0" interface, as I didn't know 
about this option until now (ie. I compiled the latest libnice without 
using this option, and it indeed fixed the situation with the docker0 

I've also read that the option "--with-ignored-network-interface-prefix" 
is provided mainly to allow the distribution maintainers to specify a 
network interface which they know is special in their distribution and 
as such should be ignored. I think that you're right and maybe it would 
make more sense if it was the _user_ of the library the one who could 
decide which network interfaces are idiosyncratic to their specific 
platform in use, and so a way to specify a list of interfaces to ignore 
at runtime would be more useful for her.

I guess this problem must have also affected Chrome and Firefox at some 
point in their development; do you have any knowledge of this? As it 
seems that they work correctly for all cases, doesn't matter if there 
are any virtual interfaces in the system, they always choose the correct 
local candidates. Checking their solutions to this problem could clarify 
a lot, so I'd like to also study those.


On 29/08/17 16:50, Olivier CrĂȘte wrote:
> Hi,
> We've seen the same thing with the libvirtd interface from KVM. And I 
> spend some time looking into this and I know Fabrice also did and we 
> couldn't find a great solution, so in commit b4abda09 he just added an 
> option to ignore one specific prefix. But maybe we should extend that 
> to a blacklist of prefixes (so we can ignore docker*, virbr*, br*. We 
> currently explicitly ignore localhost in the code, maybe we should 
> ignore more. I'm just worried that in some cases those may be 
> legitimate interfaces and may actually be the right choice. For 
> example if the peer is running inside docker!
> Olivier
> On Tue, 2017-08-29 at 16:19 +0200, Juan Navarro wrote:
>> Good afternoon,
>> I have been studying a situation where libnice chooses the wrong network
>> interface for WebRTC connections in a public-facing server: an Amazon
>> Web Services instance, where all TCP and UDP ports are totally open,
>> hosting a WebRTC application. This machine also has Docker installed for
>> other unrelated purposes. This means that there are two network
>> interfaces: eth0 and docker0, and when ICE finishes, libnice always
>> selects the IP address of the docker0 interface as the local candidate!
>> A TURN server (coturn) is used for ICE. I guess that the STUN packets
>> are able to come out through the docker0 interface, during the
>> connectivity checks, which makes this a valid candidate; however later
>> the actual WebRTC stream doesn't work at all. And it is my understanding
>> that even if it worked, it would still be an error, because outbound
>> streams would be doing a totally unnecessary loop from the local
>> application to the docker0 interface, and out of Docker to the public
>> internet. Likewise for inbound streams.
>> Running "sudo ifconfig docker0 down" solves the issue: docker0 had been
>> brought down, so now libnice chooses the correct interface, eth0 (ie.
>> the local IP address of that interface) for the local candidate which
>> gets selected.
>> This happens with the latest libnice version available on Ubuntu 16.04
>> (Xenial): 0.1.13. It also happens with the latest release of libnice,
>> 0.1.14.
>> However, this does _not_ happen with the latest development version from
>> Git, which is commit dbaf8f5: libnice now chooses the IP address
>> corresponding to the interface eth0, and the WebRTC connections work
>> fine (the RTP streams are sent and received), even if a docker0
>> interface is present.
>> Now here comes the problem: I have some other machines where there is no
>> docker0, but there are some other kind of virtual interfaces, such as
>> br-* (eg. a machine with 8 interfaces named like "br-1adb6aca2ec6",
>> which are bridged interfaces if I'm not mistaken). In those cases, the
>> latest libnice still behaves like the previous versions: one of those
>> br-* interfaces gets selected as local candidate, which makes the
>> following streams to fail reaching its destination. This even happens
>> for localhost connections! (where the Chrome browser and the libnice
>> application are running in the same machine). However bringing all of
>> the virtual interfaces down -with ifconfig- makes it work (leaving only
>> the actual network interface which has a more direct connection to the app).
>> I would like to gain a deeper knowledge of how all this works in
>> libnice, and how should I act in order to solve this problem. I guess
>> there must be lots of people out there running into the same issue, just
>> by having Docker installed, or any other software which creates virtual
>> network interfaces. So, how do you deal with this issue?
>> Kind regards,
>> Juan
>> _______________________________________________
>> nice mailing list
>> nice at lists.freedesktop.org <mailto:nice at lists.freedesktop.org>
>> https://lists.freedesktop.org/mailman/listinfo/nice
> -- 
> Olivier CrĂȘte
> olivier.crete at collabora.com <mailto:olivier.crete at collabora.com>

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