Seitenhistorie

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Description:

If one of your devices being managed by the LANCOM Management Cloud (LMC) is shown as “offline”and operated with the firmware "LCOS" is displayed as "offline", but is otherwise working functions normally, the communication with to the LMC is disrupteddisturbed. This article describes what steps for troubleshooting can be taken.

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• Enter the command tr # dns to start a DNS trace.
• Enter the command ping cloud.lancom.de to send a ping from the router to cloud.lancom.de.

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In this example cloud.lancom.de cannot be resolved.

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1.2) If the DNS cannot resolve cloud.lancom.de, you have to check whether the correct DNS server is being used:

1.2.1 Check under IPv4 → DNS → Forwarding to see whether a non-existent or malfunctioning DNS server has been specified.

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1.2.2 In the case of a plain Ethernet connection with static IP parameters, check whether the correct DNS server has been entered under Communication → Protocols → IP parameters → <name of the Internet connection>.

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1.2.3 In the case of a plain Ethernet connection with dynamic IP address assignment via DHCP from an upstream router, use LANmonitor to check whether the correct DNS server has been assigned. If the DNS server is not correct, contact the administrator of the upstream router or adjust the configuration yourself if you have access to it.

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1.2.4 Occasionally it can happen that the DNS servers assigned by the provider (statically or dynamically assigned) cannot be reached. In this case, enter a DNS forwarding under IPv4 → DNS → Forwarding to a DNS server of your choice.

• Enter the wildcard * for the Domain. This represents any number of characters. This enables the forwarding of all DNS queries.
• Set the Remote site to an IP address of a DNS server (in this example the Google DNS server).

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2) Changing the MTU on the Internet gateway (LANCOM router):

Connection problems with the LMC can also aris arise from an MTU which is too big. In this case the MTU has to be changed on the Internet gateway. 

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2.2) Open the router configuration in LANconfig and go to the menu Kommunikation → Protokolle → MTU-ListeCommunication → Protocols → MTU list. 

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2.3 Erstellen Sie einen neuen Eintrag und tragen folgende Parameter ein:) Create a new entry and change the following parameters:

• Remote site: In the dropdown-menu select the Internet connection.
• MTU: Enter the maximum packet size discovered in step 2.1), where no fragmentation is needed (in this example 
• Gegenstelle: Wählen Sie im Dropdownmenü die Internet-Verbindung aus.
• MTU: Tragen Sie die in Schritt 2.1 herausgefundene maximale Paketgröße ein, bei der keine Fragmentierung erforderlich ist (in diesem Beispiel 1464). 

2.4 Schreiben Sie die Konfiguration in den Router zurück) Write the configuration back into the router.

2.5 Damit die Anpassung der MTU Anwendung findet, muss die Internet-Verbindung einmal getrennt werden.) In order for the MTU to be used, the Internet connection has to be severed once.

Establish a connection with the CLI of the router and enter the command Verbinden Sie sich dazu mit der Konsole und geben den Befehl do Other/Manual-Dialing/Disconnect <Name der Internet-Verbindung> ein (in diesem Beispiel also of the Internet connection> (in this example do Other/Manual-Dialing/Disconnect INTERNET).

3) Further steps:

If the device in the LMC appears as “offline” even though the DNS name cloud.lancom.de is being resolved and the MTU has been changed, there are two ways to reconnect the device to the LMC.

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Generate a new activation code as described in the techpaper LANCOM Management Cloud (LMC) Rollout in the section “Assignment by activation code”, and use this code to connect the device to the LMC. The device will then reconnect to the LMC.

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