M200SC: wrong SIP communication after change of external IP address

Dear community,

I have: VDSL access with dyn. public IP <=> Fortigate FG81F <=> Snom M200SC, SIP client connected with SIP server by 1&1.

First registration of the M200 SIP clients are working well. Firewall rules are okay. Calls in both direction incl. voice streams are working.

After a change of the dyn. IP address (new 212.227.67.33) I see in a trace that the 1&1 STUN server replys with the new external IP. But the M200SC SIP client uses for SIP communication the old IP (here 46.142.151.25).

Result: SIP client is not reachable for incoming call. Perhaps 1&1 SIP server uses wrong destination address.

Are there any paramters to change this behavior? My SIP config below at the end.

192.168.2.10 local IP of M200

212.227.67.33 1&1 STUN server

No.     Time           Source                Destination           Protocol Length Info
      1 0.000000       192.168.2.10          212.227.67.33         STUN     70     Binding Request

cut

No.     Time           Source                Destination           Protocol Length Info
      3 0.022693       212.227.67.33         192.168.2.10          STUN     130    Binding Success Response MAPPED-ADDRESS: 46.142.150.27:65516 XOR-MAPPED-ADDRESS: 46.142.150.27:65516

Session Traversal Utilities for NAT
    [Request In: 1]
    [Time: 0.022693000 seconds]
    Message Type: 0x0101 (Binding Success Response)
    Message Length: 68
    Message Cookie: 2112a442
    Message Transaction ID: f915df971142ed6b820abaeb
    [STUN Network Version: RFC-5389/8489 (3)]
    Attributes
        MAPPED-ADDRESS: 46.142.150.27:65516
            Attribute Type: MAPPED-ADDRESS
            Attribute Length: 8
            Reserved: 00
            Protocol Family: IPv4 (0x01)
            Port: 65516
            IP: 46.142.150.27
        SOURCE_ADDRESS (Deprecated): 212.227.67.33:3478
            Attribute Type: SOURCE_ADDRESS
            Attribute Length: 8
            Reserved: 00
            Protocol Family: IPv4 (0x01)
            Port: 3478
            IP: 212.227.67.33
        CHANGED_ADDRESS (Deprecated): 212.227.67.34:3479
            Attribute Type: CHANGED_ADDRESS
            Attribute Length: 8
            Reserved: 00
            Protocol Family: IPv4 (0x01)
            Port: 3479
            IP: 212.227.67.34
        XOR-MAPPED-ADDRESS: 46.142.150.27:65516
            Attribute Type: XOR-MAPPED-ADDRESS
            Attribute Length: 8
            Reserved: 00
            Protocol Family: IPv4 (0x01)
            Port (XOR-d): defe
            [Port: 65516]
            IP (XOR-d): 0f9c3259
            [IP: 46.142.150.27]
        SOFTWARE
            Attribute Type: SOFTWARE
            Attribute Length: 16
            Software: Vovida.org 0.97

No.     Time           Source                Destination           Protocol Length Info
      5 5.697045       192.168.2.10          212.227.124.129       SIP      841    Request: OPTIONS sip:212.227.124.129:5060 | 

Session Initiation Protocol (OPTIONS)
    Request-Line: OPTIONS sip:212.227.124.129:5060 SIP/2.0
    Message Header
        Accept: application/reginfo+xml, application/rlmi+xml, application/sdp, application/simple-message-summary, application/watcherinfo+xml, message/sipfrag, multipart/mixed
        Via: SIP/2.0/UDP 46.142.151.25:65516;branch=z9hG4bKd77ed43c1cb12d11d;rport
            Transport: UDP
            Sent-by Address: 46.142.151.25
            Sent-by port: 65516
            Branch: z9hG4bKd77ed43c1cb12d11d
            RPort: rport
        Route: <sip:sip.1und1.de;lr>
        Max-Forwards: 70
        From: "xxxxxx" <sip:xxxxxxx@sip.1und1.de>;tag=b7a177c9bb
        To: <sip:212.227.124.129:5060>
        Call-ID: ce844fe6cd9a4186
        [Generated Call-ID: ce844fe6cd9a4186]
        CSeq: 1270186431 OPTIONS
        Allow: ACK, BYE, CANCEL, INVITE, NOTIFY, OPTIONS, REFER, SUBSCRIBE, UPDATE
        Allow-Events: refer
        Contact: <sip:xxxxxxx@sip.1und1.de;gr=urn:uuid:963e898d-8e45-4a34-88cb-000413641AF6>
        Supported: eventlist, gruu, join, replaces, sdp-anat, timer
        User-Agent: snomM200SC/2.11.0.4-0
        Content-Length: 0

No.     Time           Source                Destination           Protocol Length Info
      6 5.718627       212.227.124.129       192.168.2.10          SIP      407    Status: 200 OK | 

    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 46.142.151.25:65516;branch=z9hG4bKd77ed43c1cb12d11d;rport=65516;received=46.142.150.27
            Transport: UDP
            Sent-by Address: 46.142.151.25
            Sent-by port: 65516
            Branch: z9hG4bKd77ed43c1cb12d11d
            RPort: 65516
            Received: 46.142.150.27
        From: "xxxxxx" <sip:xxxxx@sip.1und1.de>;tag=b7a177c9bb
        To: <sip:212.227.124.129:5060>;tag=9fca323d66201399418559aa37dc2bce.6114ada2
        Call-ID: ce844fe6cd9a4186
        [Generated Call-ID: ce844fe6cd9a4186]
        CSeq: 1270186431 OPTIONS
        Server: UI Kamailio
        Content-Length: 0

M200: