Using ethernet port for point-to-point communication

Ward

I have some troubles figuring out the board IP when connecting a computer directly with the Bela

[Win10 laptop] --> [USB3.0 to ethernet] --> [ethernet cable] --> [BBB]

In this scenario I am able to access the IDE through bela.local, when I then type ip addr show eth0 in the IDE console it only show a inet6 line, and no inet line. I am able to ssh into the Bela using the IPv6 but I'd prefer to also have a IPv4 assigned, as I will disable the IDE in the future, and then my only way of retrieving the IP is through typing over characters displayed on an OLED, which in the case of an IPv6 is a pain..

I read on the IP addresses page that the Bela runs a DHCP server so that addresses can be assigned. Do I have to modify /etc/dhcp/dhcpd.conf and tell it to also assign an IPv4?

giuliomoro

the ethernet port (eth0)'s default configuration expects to be connected to a router or other device that runs its own DHCP server. If you are trying to do a point-to-point network, you should either set the board and the host computer to a static IP, with no DHCP server involved, or set the board to a fixed address and enable the DHCP on the appropriate address range.

So for instance in /etc/network/interfaces you could set

allow-hotplug eth0
iface eth0 inet static
    address 192.168.10.2
    netmask 255.255.255.0
    network 192.168.10.0

then the board's eth0 port will have address 192.168.10.2. Then:

either set the host computer's static IP on the relevant port to 192.168.10.1 (or other address in the valid range)

or on the board in /etc/dhcp/dhcpd.conf add

subnet 192.168.10.0 netmask 255.255.255.0 {
        range 192.168.10.1;
}

so that it automatically assigns the IP to the host computer.

Ward

giuliomoro So for instance in /etc/network/interfaces you could set

So I wrote a bit of code that modifies this file and allows you to switch between static/dynamic, and if static specify an IP, use 255.255.255.0 as netmask and uses the specified IP with the last part set to 0 as network:

getInterfaceLines() {
  auto ipv4 = parEthernetIPv4.getValueString();
  auto lastDot = ipv4.find_last_of('.');
  auto network = ipv4.substr(0, lastDot + 1);
  return "iface eth0 inet static\n    address " + ipv4 + "\n    netmask 255.255.255.0\n    network " + network + "0";
}

Now if I want to apply this I can call system("sudo reboot") (and that works), but I wonder if there is a way to do it without fully rebooting Linux?

Ward

I actually found out you do not necessarily have to switch to a static IP, as IPv6 requires every device on a local network to have a link-local address assigned. Thus by having this IPv6 address assigned bela.local is accessible even if there is no DHCP server on the network.

In my use case, I had to switch my Rust webserver to listen to IPv6 instead of IPv4 and now it works using Bela <--> laptop but also using Bela <--> router <--> laptop.

giuliomoro

ah good news

Ward

Am I correct in saying that Osc sender/receiver only support IPv4?

giuliomoro

Yes. Not sure how hard it is to make it work with ipv6. What do you need ipv6 for?

Ward

I'm using ethernet for a webserver and for an ethernet CV/gate expander using OSC. I would like to make it as plug and play as possible, but I don't want to set static IP's or run a DHCP server on the Bela. Static IPs can collide with a DHCP server, and a DHCP server probably gives trouble if there is another DHCP server also present..

As for the webserver running on the Bela, I've solved this by having it listen to any http requests made over IPv6. The user types in bela.local and this address points either to an IPv4 when a DHCP server is present, or to the Bela's (IPv6) link-local address. Either way, with or without router, the user can reach the webserver.

For OSC, I'm having the CV/gate expander send messages to bela.local every now and then, the Bela pulls the IP address from the received OSC message and uses that to send messages back. This approach only works when the devices are on a network with a DHCP server, as OSC currently only works with IPv4. If IPv6 were also supported, this situation would work even without a DHCP present. When plugging the Bela directly into the CV/gate expander, I can see both devices always get an IPv6 address.

The IPv4 and IPv6 API seem similar on a first glance. It says here that the IPv6 can also handle IPv4 stuff as an IPv6 can contain an IPv4.

Pd netsend supports IPv6 since 0.51 and also works when you specify bela.local as address to send OSC to. As far as I can tell getifaddrs is used to lookup the IP corresponding to bela.local. I found an example here.

I have to focus on some other stuff due to Dutch Modular Fest next week, and I'm okay with bringing a router, but maybe I can have a look at this in the future because IPv6 would make it plug and play for the musicians.

giuliomoro

/etc/init.d/networking restart (or maybe it's neater systemctl restart networking)
(perhaps followed by ifup --force) may do it? There surely are better ways without modifying that file ...

For instance, a quick man ifup shows that you can specify a different configuration file from /etc/network/interfaces with --interfaces=FILE, so you could make a dedicated temp file with this configuration and then call ifup with it. Or even not have any file at all and use bash's process substitution, e.g.:

ifup --interfaces=<(echo -e "iface eth0 inet static\n    address ${IPV4}\n    netmask 255.255.255.0\n    network ${NETWORK}0")

This one also looks promising:

       -o OPTION=VALUE
              Set OPTION to VALUE as though it were in /etc/network/interfaces.

though I am not sure about the actual syntax, because there's no OPTION=VALUE in /etc/network/interfaces, so it may need a bit of trial and error.

Ward

Hey and do you know how to get the DHCP client to query the server/router for a dynamic IP?

I think I tried this one yesterday /etc/init.d/networking restart and it seemed to not get an IP assigned, only when booting.

giuliomoro

dhclient eth0 should do it

Ward

And the other way around? How would I remove the dhcp assigned IPs when switching from dhcp to static?

giuliomoro

Maybe ifup specifying a file with --interfaces as shown above?