Reaction of Equipment after Change of IP-Number?

Discussion in 'VOIP' started by Wolfgang Barth, May 22, 2005.

  1. I'm using VoIP behind a NAT Modem-Router from Netgear and a Sipura
    SPA3000 for inbound and outbound telephony from all my phones.

    But I get a new IP-number at least once a day from my DSL Provider.
    After this number change the Sipura failes to reregister correctly.

    Does anybody have problems with these IP-number changes?
    How do you solve this?

    Wolfgang Barth, May 22, 2005
    1. Advertisements

  2. Wolfgang Barth

    Rick Merrill Guest

    Your configuration should look like this:

    and all four devices should use DHCP to get IP and DNS addresses.
    Rick Merrill, May 22, 2005
    1. Advertisements

  3. Wolfgang Barth

    Miguel Cruz Guest

    Fortunately my IP address only changes every two or three weeks. But my
    Sipura 1001 has the same problem.

    If I go to any of the admin pages on its web interface and click the button
    to save changes (even though I haven't made any changes) it immediately
    re-registers properly.

    I imagine that after some timeout interval it might straighten itself out as
    well but I've never been patient enough to wait and see.

    Miguel Cruz, May 22, 2005
  4. Wolfgang Barth

    Ivor Jones Guest

    You are using DHCP on the router and using private IP addresses on all the
    connected devices, aren't you..?

    Ivor Jones, May 22, 2005
  5. Yes. I do use a modem-router from Netgear with port restricted cone NAT.

    This is my DHCP source for my private LAN, where the SIPURA is in.

    Everything works properly. Even NAT traversal.
    The only problem is that reregistering(?) and/or NAT stay alive(?) tend
    to fail after change of the EXTERNAL IP-Number.

    Wolfgang Barth, May 22, 2005
  6. But I have a modem-router with DHCP and behind that there is the SPA3000
    and the PCs. I cannot change this configuration.
    PCs and Sipura do use DHCP to get local IP and DNS addresses.
    The modem-router gets its via PPPoE.

    Wolfgang Barth, May 22, 2005
  7. Wolfgang Barth

    Rick Merrill Guest

    Why not? How do you expect the SPA3000 to do QoS?
    Why is that?
    Rick Merrill, May 23, 2005
  8. Wolfgang Barth

    Miguel Cruz Guest

    Yes, the problem is that the Sipura device doesn't have any way of being
    actively alerted that the external IP of the router has changed, so it
    constructs its SIP headers incorrectly.

    I suppose it could be configured to check more frequently (with the STUN
    server or something); I haven't been sufficiently motivated to look into it
    further yet though.

    Miguel Cruz, May 23, 2005
  9. Wolfgang Barth

    wkearney99 Guest

    Fortunately my IP address only changes every two or three weeks. But my
    If it's DHCP then it should come with a lease time. Does the sipura ignore
    the lease time?
    wkearney99, May 23, 2005
  10. Wolfgang Barth

    Ivor Jones Guest

    It doesn't *need* to know. All the Sipura needs to know is the private IP
    address of the router, usually or something similar. It
    doesn't know or care about the public IP address, only the router does.

    My connection has what I call a semi-static IP address, in that it can
    stay the same for weeks on end then change for no apparent reason..! My
    Sipura has never failed to register because of it.

    Ivor Jones, May 23, 2005
  11. For example, because the router handles the PPPoE decoding and NATting.
    Because that's how things work when your provider uses PPPoE and gives
    you only one IP address (assigned through PPPoE), which obviously can't
    be shared among devices: hence the need for NAT functionality, and
    often the DHCP service to assign the local IP addresses, both of which
    can be provided by the route.

    That said, I have the same configuration as Wolfgang's (SPA-3000 behind
    the NAT router) and never noticed that problem. On the other hand, I
    used to have a different type of problem with a Netgear MR814v2
    ). Now I'm running Linux on a Linksys WRT54G ( ) and
    Netgear is only a painful memory :)

    The nice thing of using Linux as router is that one can run tcpdump to
    capture packets to a file, transfer the file to a bigger machine and
    inspect them with Ethereal. This would tell you more about why the
    re-registration fails: which is a quite unusual thing. Wolfgang, are
    you sure it fails? Or perhaps is it not repeated often enough, so that
    after the change of IP address the remote SIP registrar still remembers
    the old address? In that case, you could try to reduce the
    re-registration interval of the SPA-3000 to, say, a couple of minutes.
    You can do this putting 60 (the number of seconds) in the "Register
    Expires:" field of the "Line 1" and "PSTN Line" screens of the Admin

    Another way of inspecting the SIP packets would be installing a NON
    switching 10baseT hub between router and SPA-3000, and use it just like
    a T-joint to tap into the traffic with a monitoring machine directly
    running Ethereal. Unfortunately, in these days non-switching hubs are
    hard to find.

    Enzo Michelangeli, May 24, 2005
  12. Actually it _should_ care, in order to meet the SIP specifications; but
    some registrar proxies flat-out ignore the SIP headers and use, as IP
    address and UDP port, the same present as source on the headers of the
    packet that contained the registration request. This violation of the
    SIP specs often saves the day, but sometimes the results turn out to be
    annoying because it prevents third-party registration. Before
    understanding what was going on, I wasted days trying to register a
    Sipura SPA-3000 on multiple registrars using a utility, Sipsak
    ( running on a PC on the same LAN. I did that because
    the SPA-3000, due to a silly firmware limitation, can place calls
    through several outbound proxies BUT can register only on one of them.
    Well, it didn't work, despite the fact that I passed all the right
    parameters to Sipsak and Sipsak prepared the SIP headers accordingly:
    the registrar always registered the SPA-3000 at the UDP port mapped as
    source by the NAT router for the packets coming from the Sipsak client,
    which of course was different from the one I had specified for the
    SPA-3000 :-(

    Moral of this story: if you deal with NATs, whenever possible avoid SIP
    like the plague, and use IAX2.

    Enzo Michelangeli, May 24, 2005
  13. Wolfgang Barth

    Miguel Cruz Guest

    I think we can take it for granted that if the thing is doing anything at
    all, it knows its proximal router's address.

    But if you sniff SIP traffic you will probably see your external (outside of
    NAT) IP address communicated in the payload (not just in packet headers). At
    least I do between my Sipura (inside NAT) and Asterisk server (in the wild).

    Miguel Cruz, May 24, 2005
  14. Register expires is 3600 seconds in the moment. But reregistering failed
    several times after IP-change. At least for 10 hours. But I will give it
    a try an reregister earlier.
    In this moment I have this combined modem-router, so I do not want to
    change hardware.

    Thanks for the hints.

    Wolfgang Barth, May 24, 2005
  15. Seams so.

    Wolfgang Barth, May 24, 2005
  16. Wolfgang Barth

    Ivor Jones Guest

    I've got a 16 port 10-base-T hub if anyone wants it..! Redundant since I
    upgraded all my stuff to 100-base-T.

    Ivor Jones, May 25, 2005
  17. By the way, which NAT-related options have you set under "NAT Support
    Parameters" in the SIP screen of the Admin interface? I have set
    everything to "yes" with the exception of "Send Resp To Src Port:"
    which is a "no"; "STUN Server:" points to ""; "EXT
    RTP Port Min:" and "EXT IP:" are both blank, and "NAT Keep Alive
    Intvl:" is set to "15".

    Enzo Michelangeli, May 25, 2005
  18. Wolfgang Barth

    Rick Merrill Guest

    I thought you said the sipura was given a fixed IP...
    Rick Merrill, May 25, 2005
  19. Ok. I'll think about this. But as far as I understood its necessary to
    set "Send Resp to src port" to yes because my router users "port
    restricted cone NAT".

    But its working ok since two days now. No idea why.

    Wolfgang Barth, May 25, 2005
  20. Internally it uses DHCP but based on the MAC it will always be the same.

    But the problem is with the EXTERNAL IP-number which is very different
    each day.

    Wolfgang Barth, May 25, 2005
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.