[SR-Users] Having kamailio bind to a VRF device

George Diamantopoulos georgediam at gmail.com
Wed Oct 11 23:07:42 CEST 2017


Hello Daniel,

I'm including the original sketch for clarity:

 +----------+      +-------------------+
 |   eth0   |      |    vrf-green      |
 | 1.1.1.1  |      |    127.0.0.1      |
 +----------+      +-------------------+
                            |
                      +----------+
                      |   eth1   |
                      | 2.2.2.2  |
                      +----------+

Thanks for the reply. Indeed, using the advertise option for the "listen"
directive will result in kamaiio no longer failing to start when using
force_send_socket(2.2.2.2:5060) with 2.2.2.2 being used in the "advertise"
option.

However, this doesn't make much of a difference in that kamailio still
won't process IP packets arriving on eth1 at IP 2.2.2.2... I can see
OPTIONS coming with sngrep, but nothing in the logs, no replies, only
retransmissions from the originator.
In addition, while without VRF kamailio will select the right interface
with mhomed=1, this is no longer the case.
Also, If I try to send something to a host with force_send_socket, the
transaction fails with 477 Unfortunately error on sending to next hop
occurred. In the log, kamailio prints something along the lines of:
udp_send(): sendto(sock,0x7f5c4f937d08,1888,0,9.9.9.9:5060,16): Invalid
argument(22)
udp_send(): invalid sendtoparameters
msg_send_buffer(): udp_send failed
where 9.9.9.9 is the $dd and presumably force_send_socket(2.2.2.2:5060) has
been called before t_relay()

Also, I additionally found out that if the networking configuration is as
follows:

 +----------+      +-------------------+   +-------------------+
 |   eth0   |      |    vrf-green      |   |    vrf-red        |
 | 1.1.1.1  |      |    127.0.0.1      |   |    127.0.0.1      |
 +----------+      +-------------------+   +-------------------+
                            |                       |
                      +----------+            +----------+
                      |   eth1   |            |   eth2   |
                      | 2.2.2.2  |            | 3.3.3.3  |
                      +----------+            +----------+

Then this won't work for vrf-red:
listen=vrf-green:5060 advertise 2.2.2.2:5060
listen=vrf-red:5060 advertise 3.3.3.3:5060
One needs to use different IPs for the MASTER devices (say 127.0.0.1 and
127.0.0.2) for kamailio to startup with the above listen directives.

It's a bit surprising it doesn't work. According to a user on cumulus slack
channel (cumulus contributed the VRF code to the linux kernel): "any app
that has a command line or option switch to call SO_BINDTODEVICE on the
sockets can be configured to use any VRF".

I guess the problem lies in that kamailio binds to several sockets and
there are multiple routing tables to consult, so mhomed doesn't work as
expected (if every table has a default route and nothing more specific than
that). But still, this doesn't really explain why binding to the VRF master
net devices doesn't work (I mean, "ping -I vrf-green" works just fine for
ping)...

I don't think VRF support is very useful for most users though, I just had
one corner case I needed to tackle and VRF seemed like an easy fix. I'll
think of an alternative at some point, I guess.

On 26 September 2017 at 09:52, Daniel-Constantin Mierla <miconda at gmail.com>
wrote:
>
> Hello,
>
> I haven't worked with vrf here, so no first hand experience ...
>
> What happens if you try with next option?
>
> listen=vrf-green:5060 advertise 2.2.2.2:5060
>
> Cheers,
> Daniel
>
>
> On 25.09.17 19:10, George Diamantopoulos wrote:
>
> Sorry to bump this, but it would be very useful if I knew whether there's
any point in pursuing this or not. Any hints?
>
> On 21 September 2017 at 14:06, George Diamantopoulos <georgediam at gmail.com>
wrote:
>>
>> Hello,
>>
>> I have a use case where I need to have kamailio bind to a VRF device.
The configuration in question is similar to the example below, where eth1
is a slave to the VRF-lite device:
>>
>>  +----------+      +-------------------+
>>  |   eth0   |      |    vrf-green      |
>>  | 1.1.1.1  |      |    127.0.0.1      |
>>  +----------+      +-------------------+
>>                             |
>>                       +----------+
>>                       |   eth1   |
>>                       | 2.2.2.2  |
>>                       +----------+
>>
>> Both the main routing table and "vrf-green" routing table have a default
route.
>>
>> What I need to be able to do is have kamailio bind to both interfaces:
>>
>> listen=eth0:5060
>> listen=vrf-green:5060
>>
>> And additionally be able to use force_send_socket to select an
interface, for example:
>>
>> force_send_socket(udp:2.2.2.2:5060);
>>
>> However, I can't get this to work. The above configuration fails because
there is no listen directive for 2.2.2.2. Also, kamailio doesn't process
packets received on the VRF with the above listen directives, it behaves as
if it doesn't listen on 2.2.2.2 indeed.
>>
>> In addition using either of the below:
>>
>> listen=udp:2.2.2.2:5060
>> or
>> listen=eth1:5060
>>
>> fails with an error upon starting kamailio.
>>
>> According to the kernel documentation:
>>
>> Applications that are to work within a VRF need to bind their socket to
the
>> VRF device:
>>
>>     setsockopt(sd, SOL_SOCKET, SO_BINDTODEVICE, dev, strlen(dev)+1);
>>
>> or to specify the output device using cmsg and IP_PKTINFO.
>>
>> The question is, is VRF useable with kamailio right now? Or is
development needed? Thanks!
>>
>> BR,
>>
>> George
>
>
>
>
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>
>
> --
> Daniel-Constantin Mierla
> www.twitter.com/miconda -- www.linkedin.com/in/miconda
> Kamailio Advanced Training - www.asipto.com
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