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Raymarine - Cerbo - Internet connection walkthrough

There are many threads about the issues connecting a Raymarine Axiom to the Cerbo while maintaining internet connection. I have tested @mvader (Victron Energy) ‘s suggestion here, and I can confirm that it works .

The main issue is that

- Axiom only displays the Victron app when connected over Ethernet

- Axiom wants to be the dhcp server in the network (and even if the dhcp server option in turned off in newer Lighthouse) it does not accept IP addresses from normal routers

If the Cerbo is connected to the same network as the Axiom, and Cerbo is using the dhcp server of the Axiom (this is the default configuration), it will use the Axiom as the default gateway. The default gateway is the device through which packets are routed to in case the Cerbo needs to access the internet. If the Axiom is connected to the Internet over its wifi, it will provide Internet access to the connected devices, so the Cerbo can access the internet over the Axiom. However, this only works if the chartplotter is on all the time, and has the disadvantage of being over wifi connection.

So in case this is not acceptable, the workaround is to place the Cerbo, the router and the Axiom into the same subnet, ignore the dhcp of the Axiom and set both the IP configuration and set the default gateway manually on the router and the Cerbo

I have found that the Axiom uses long dhcp leases, so in case a device has an IP address from the Axiom, it will keep the address for very long.

1. The ip network that the chartplotter is using needs to be determined. It seems that different versions use different subnets, so there is no shortcut,

If you connect your notebook to the Axiom directly, it will receive an IP address. You can check the ip configuration in the command line by typing ipconfig. In my case it was

Link-local IPv6 Address . . . . . : fe80::cd72:55da:1896:e457%21

IPv4 Address. . . . . . . . . . . :

Subnet Mask . . . . . . . . . . . :

Default Gateway . . . . . . . . . :

1. Based on the information above, the subnet network needs to be determined. There are many services that do the calculation for you, for example, here: The ip address and the subnet mask needs to be entered and it returns the network information. In our case:

IP Address:

Network Address:

Usable Host IP Range: -

Broadcast Address:

Total Number of Hosts: 2,048

Number of Usable Hosts: 2,046

Subnet Mask:

Wildcard Mask:

Binary Subnet Mask: 11111111.11111111.11111000.00000000

IP Class: B

CIDR Notation: /21

IP Type: Public

Short: /21

1. In order to make all three devices see each other, the Axiom and the Cerbo devices need to be connected to the LAN ports of the router and the IP address of the Cerbo and the router need fixed and to be entered manually. But don’t connect them just now.

In theory you could use any IP from the range: - as it was returned in the network subnet calculator above. However, as we don’t know if Raymarine has implemented any logic in giving out IP addresses, it is best to ask the Axiom’s dhcp to give you an address and stick to the one given. First, connect the Cerbo to the Axiom and write down the IP address that it has received. (We already know the netmask)

1. After that, router’s LAN interface should be set to a fixed ip address and the dhcp should be disabled. Attention, if you disable the dhcp server in the router, you might not be able to log in again.

In order to make sure that you don’t loose access to the router, it is best to check the MAC address of the router’s LAN interface somewhere on the admin screen of the router. After that, you should temporarily set the MAC address of the router to be the ethernet MAC address of your notebook. This can be done in the device manager. One description of how it works could be found here:

If you plug in your notebook to the Axiom and check your IP address the same way as we did above you should get the IP that the Axiom has designated to the router. In our specific case it was:

Link-local IPv6 Address . . . . . : fe80::52a0:1c7:e22e:4098%21

IPv4 Address. . . . . . . . . . . :

Subnet Mask . . . . . . . . . . . :

Default Gateway . . . . . . . . . :

Write down the IP address and don’t forget to set the MAC address back to default.

1. Log in to the router, disable the dhcp on the LAN and set the LAN network address to the one given by the Axiom (in our example, the subnet mask as it was shown (in our case With many routers you need to set the broadcast IP (you can see it in the calculator in 2.). Maybe, the dns server needs to be specified as well. It is easiest to use the one from Google, because it is easy to remember, just enter and if a second other address is needed for the dns, can also be used.

After that, you will loose access to the router, but after a router restart if both your computer and the axiom is connected to the router at the same time the router will be accessible again uaing the IP address manually specified.

1. Lastly, what needs to be done is to manually set the IP address of the Cerbo and the gateway IP to the IP of the router (in our case plus the dns and netmask of the same as above. After plugging in the cerbo to the router and the Axiom to the router, it should have internet access.

With this solution, the Cerbo and the router will have both access to the internet and thus to the VRM regardless of the Axiom.

The only caveat is that in most routers the wifi and the lan networks are bridged. This means that if any other device is used on the local network, its IP and default gateway needs to be set manually in order to access the internet. Also, with this approach the Axiom is not able to communicate with the router over wifi, so if wifi was used in the past for updates on the Axiom, it won’t work anymore.

The professional solution would be to segregate the network ports used in the Axiom network (cerbo, axiom, maybe radar) into a specific vlan, and to create another network for wifi connections and the potentially remaining free lan ports and to set up the traffic rules between the zones. This, however, is way beyond our scope. Probably no home routers provide this feature, but the new firmware for Teltonika and MicroTik should support this.

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