question

Henk van Rooyen avatar image
Henk van Rooyen asked

Cerbo GX duplicate IP addresses

Hi:

(originally posted here, but realise my problem is actually different)

Home network controller (UniFi) complains about duplicate IP addresses on the network. On further inspection this is somehow related to the Cerbo WiFi packets "leaking" onto the wired LAN.

Ethernet settings:

victron-lan-settings.jpg

WiFi settings:

victron-wifi-settings.jpg


Duplicate IP address on Ethernet:

victron-duplicate-ip.jpg

Note the detail box to the right of the screen grab, indicating that Victron HMI, connected by wire, has an IP address which belongs to "Einstein". Details of "Einstein" below:

einstein-detail.jpg

What I find really weird is the intermittency of the problem. Every few seconds the wired 172.29.12.145 device drops its "nom de plume", and transmits correctly again:

victron-revert-to-single-ip.jpg

Note on the right of the screen how the same device, connected to the same port on the same switch, now has a different (correct as per Ethernet settings!) IP address.


To add to the weirdness, here is the Link-Local interface doing the same:

victron-link-local-duplication.jpg


Background, in case someone asks why I maintain two connections: Cerbo is connected to LAN via Ethernet as well as WiFi to try and avoid repetition of an incident where the Victron intermittently lost connectivity a few months ago, causing me to replace a switch as well as the Cerbo without fixing the problem. So just to be very explicit about this: I had a Cerbo which lost connectivity. I replaced the switch to no avail. I purchased a new Cerbo and set it up from scratch, and the problem still persisted. This may have been related to a firmware upgrade and may even have been fixed in a later update - I would not know. I also appreciate that I can just switch off WiFi (which does seem to fix the problem), but fact remains the device should not be doing this. As a last comment, I somehow suspect the current problem may not be unrelated to the one I just described.


If this is indeed a bug and I should report it elsewhere, please advise.


TIA

H

cerbo gxconnection issueTCP IP Networking
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2 Answers
Meine_Energiewende avatar image
Meine_Energiewende answered ·

Hi ! You use a /23 as your netmask.

So the network range is from 172.29.12.0 to 172.29.13.255 -> both are in the same network (and same broadcast domain).

Linux (which runs on the cerbo) sometimes sends arp requests for both interfaces (wireless and ethernet) from the same source. This is seen as a duplicate on your ubiquity.

The Problem itself is called "arp flux" and is described here :

http://linux-ip.net/html/ether-arp.html#ether-arp-flux

This should (in most cases) solf the problem:

echo 1 > /proc/sys/net/ipv4/conf/all/arp_filterecho 1 > /proc/sys/net/ipv4/conf/eth0/arp_filterecho 1 > /proc/sys/net/ipv4/conf/wifi0/arp_filterecho 1 > /proc/sys/net/ipv4/conf/all/arp_ignore
echo 2 > /proc/sys/net/ipv4/conf/all/arp_announce


You have to make it reboot safe via sysctl.conf

Hope it helps

Jens


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Henk van Rooyen avatar image Henk van Rooyen commented ·

Ah! ARP flux will explain it. Thank you very much.


Yes. /23 netmask. I ran out of addresses with a /24 netmask. What can I say. The geek in me sometimes gets carried away.


/*Wanders off to read about why Linux does such an apparently bonehead thing*/


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JohnC avatar image
JohnC answered ·

Hi @Henk van Rooyen

Networking issues can be very personal. But I use different addresses for the ethernet and wifi. Even different subnets. VRM can see them too..

1672138645171.png

They're underlined, so can take a mouseclick, and selection of either takes me straight to Remote Console. That's instant, so is local, not via the server.

Both mine access WAN wifi via the same modem. Maybe try different addresses. I can recall mine were originally set via DHCP, but I just changed them to manual via the GX screen and they've rolled on unchanged ever since.


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