tun device setup is failing

[rajesh1084]

container-networking/4-overlay-network/setup.sh

Line 56 in 69015b5

sudo socat TUN:$TUNNEL_IP/16,iff-up UDP:$TO_NODE_IP:9000,bind=$NODE_IP:9000 &

This command expects a UDP server to be running on the target node ($TO_NODE_IP) on port 9000. Otherwise, we get the following error:

$ sudo socat TUN:$TUNNEL_IP/16,iff-up UDP:$TO_NODE_IP:9000,bind=$NODE_IP:9000
2024/06/10 05:27:47 socat[4826] E read(7, 0x5e426d5e2000, 8192): Connection refused

I tried running a small UDP echo server on both nodes on port 9000 and slightly modified the socat command in setup.sh to make it work-

$ sudo socat TUN:$TUNNEL_IP/16,iff-up UDP:$TO_NODE_IP:9000,bind=$NODE_IP:9001

Is there any misunderstanding? Shall I send a pull request?

[rajesh1084]

@kristenjacobs: I must say this has been very useful in understanding the basics of container networking. Thanks for sharing this.

[dongho-jung]

I ran into exactly the same problem!

However, even after changing it to TUN:$TUNNEL_IP/16,iff-up UDP:$TO_NODE_IP:9000,bind=$NODE_IP:9001 and running nc -ukl 9000 & on each node, the connection is still not working properly.

When I run ip a on the node, it shows something like this:

45: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1492 qdisc fq_codel state UNKNOWN group default qlen 500
    link/none
    inet 172.16.0.100/16 scope global tun0
       valid_lft forever preferred_lft forever
    inet6 fe80::adbb:e4a1:93e:1258/64 scope link stable-privacy
       valid_lft forever preferred_lft forever

Looking at the state UNKNOWN, it seems like the tun0 interface is not being configured properly.

If anyone has successfully completed the last hands-on, please help!

[rajesh1084]

@dongho-jung , this is to do with the socat version. The version used in this repo is v1.7.3.1. The one you are using may be the latest.

[dongho-jung]

@rajesh1084 Thank you so much. 😊😊👍👍👍

The only environment I currently have available is an M1 Mac, so when I use Vagrant, I could only use the ARM architecture. Because of that, instead of using vm.box = "ubuntu/xenial64" as in the original setup, I had to use vm.box = "net9/ubuntu-24.04-arm64".
As a result, I was unable to use the .deb files that were locked in the original repository.

Instead, I was able to install the same version for the ARM architecture in the following way.

wget http://launchpadlibrarian.net/362322446/libssl1.0.0_1.0.2n-1ubuntu5_arm64.deb
wget http://launchpadlibrarian.net/236103162/socat_1.7.3.1-1_arm64.deb
sudo dpkg -i libssl1.0.0_1.0.2n-1ubuntu5_arm64.deb
sudo dpkg -i socat_1.7.3.1-1_arm64.deb

Unfortunately, commands like sudo socat TUN:$TUNNEL_IP/16,iff-up UDP:$TO_NODE_IP:9000,bind=$NODE_IP:9000 or sudo socat TUN:$TUNNEL_IP/16,iff-up UDP:$TO_NODE_IP:9000,bind=$NODE_IP:9001 didn’t work properly for me. It seems like I might have misconfigured the UDP echo server, which is likely the cause of the issue.

(For reference, I started the UDP echo server using the following command: socat udp-listen:9000,fork exec:cat &)

As a result, I was able to set up the overlay network as follows, and I’m sharing it:

1. First, open UDP port 9000 on each node using socat udp-listen:9000,reuseaddr tun:172.16.1.100/16,up &.
2. Replace socat TUN:$TUNNEL_IP/16,iff-up UDP:$TO_NODE_IP:9000,bind=$NODE_IP:9000 & with socat udp:$TO_NODE_IP:9000 tun:$TUNNEL_IP/16,up & in setup.sh.