Double NAT – One Way Audio

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Asterisk Users 6 Comments

I have a setup which is not working right now:

Provider – DSL-Router (192.168.2.1) – Bintec-Router (10.17.46.66) – Asterisk (10.17.46.99)

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My issue: Everything works, but RTP is only going from my Asterisk towards the provider. Asterisk is configured to use SIP-ports 55060 and RTP-ports 51000-51999. Those ports are forwarded on DSL-router to the bintec router and from the bintec router to asterisk.

What I see is the Invite from provider goes to 192.168.2.1 and rtp port 7070. my asterisk responds with audio to be sent to ip address 80.142.12.12 port 51242. Afterwards RTP goes from 10.17.46.99:51242 to 192.168.2.1:7070. but the RTP back is not coming in.

I would expect the RTP traffic to be sent to 80.142.12.12 (internal 192.168.2.1) port 51242 – then i would have successfully two way audio. But why is port 7070 used?

The DSL-router is a speedport w724v type A.

6 thoughts on - Double NAT – One Way Audio

  • Hi Andre,

    Some routers just simply won’t support this double-nat scenario you describe. Othera will… And without any special forwarding.

    Is it possible to put the first router into “bridge” mode, and use the second router as the actual NAT router?

    This may be the quickest solution to your problems. Good luck!

    Thanks, Glenn (mobile)

    Hi all,

    I have a setup which is not working right now:

    Provider – DSL-Router (192.168.2.1) – Bintec-Router (10.17.46.66) –
    Asterisk (10.17.46.99)

    My issue: Everything works, but RTP is only going from my Asterisk towards the provider. Asterisk is configured to use SIP-ports 55060 and RTP-ports
    51000-51999. Those ports are forwarded on DSL-router to the bintec router and from the bintec router to asterisk.

    what I see is the Invite from provider goes to 192.168.2.1 and rtp port
    7070. my asterisk responds with audio to be sent to ip address 80.142.12.12
    port 51242. Afterwards RTP goes from 10.17.46.99:51242 to 192.168.2.1:7070. but the RTP
    back is not coming in.

    I would expect the RTP traffic to be sent to 80.142.12.12 (intetnal
    192.168.2.1) port 51242 – then i would have successfully two way audio. But why is port 7070 used?

    The DSL-router is a speedport w724v type A.

    regards, andre

  • Hi Glenn, unfortunately there is no bridge mode or any comparable mode available. I
    am using the same router (but another type) on my private homenetwork with another router at the back (=> same architecture as in this failing scenario), but everything works fine. There are only two differences:
    1. Another Type (w724v Type B instead of w724v Type A)
    2. No VoIP services used by w724v (which is on Type A hardware currently the case, maybe disablling them helps?).

    I will check to switch 2., but that is not easily doable because there are productive numbers used… The asterisk installation is currently in development…

    regards, andre

  • ISP won’t change, but will check. in the hidden menus it isn’t changeable either.

    However, it is working after i deactivated VoIP in the router. And even after reenabling VoIP it is still working. I don’t understand why… However, it works. 😀

    thanks a lot.

    regards, andre

  • Can you get your own modem? (double) NAT is ugly hack.

    Not sure what is VoIP in the router here, but looks like some sort of SIP ALG
    or VoIP passthrough – disable it! It rewrites ip addresses inside of the packets ang it generally messes things up. Also make sure your asterisk can get correct public IP – “externip=” … Martin

  • Unfortunately not. The provider is only supporting this hardware.

    ALG
    can

    Would like to disable it, but this hardware is not supporting it. Neither by standard GUI nor by hidden menu… 🙁

    regards, andre