Cannot connect to the public internet from a UBOS container
/docs/gears/faq-howto-troubleshooting/error-container-cannot-connect/
A variety of things can be the root cause of that, and we don’t have a full list. Chances are that your host operating system is not correctly configured for networking containers. Here is a list of things to check:
-
On your host, a new network interface is generated just for the UBOS container. Using:
% ip addr
check that such an interface appears when you create the container, and it has a suitable IP address such as
10.0.0.1
. If not, check that you are runningsystemd-networkd
on the host with a suitable configuration file. -
In your UBOS container, using:
% ip addr
make sure your container has a corresponding IP address such as
10.0.0.2
on an interface calledhost0@ifX
for some value ofX
. If your interfacehost0@ifX
does not have an IP address, tryip dev set host0 up
. There seem to be some combinations of systemd versions between host and container in which thehost0
interface in the container does not automatically come up. -
Test that you can ping the container from the host, and the host from the container with a command such as:
% ping 10.0.0.1
If you can’t and both host and container have correct IP addresses, make sure your host does not run a firewall that prevents the communication from happening.
-
If the container can communicate with the host, and the host with the public internet, but the container cannot communicate with the public internet, chances are that some of the involved network interfaces aren’t forwarding packets. This is common because most Linux distros deactivate packet forwarding by default. The simplest way to globally switch on packet forwarding on the host is to execute, on the host:
% sudo sysctl net.ipv4.ip_forward=1
If this fixes the problem, you can make it permanent by telling systemd about it with a configuration file such as
/etc/systemd/network/wired.network
with content:[Match] Name=en* [Network] DHCP=ipv4 IPv4Forwarding=1 IPv6Forwarding=1
You may have a file like that already, except for the
IPv4Forwarding=1
andIPv6Forwarding=1
statements. -
In your container, try to connect to some well-known IP address, like:
% ping 8.8.8.8
If you can connect, check DNS, with something like:
% dig ubos.net