Failed to setup DHCP in n2n network

[maaarcus]

Hi all,

I've been using n2n and it worked wonderfully. I like how I can broadcast UDP even with cloud VMs using n2n.

To scale out my application, I will need DHCP to be working on n2n. However, there are little documentation. So I tried my best to get it working and I failed. I've put the details of my DHCP setup in the below post:
https://stackoverflow.com/questions/64403178/n2n-cannot-setup-dhcp-server-on-n2n-vpn-network

n2n version: n2n v.2.8.0.r540.53afd3c

Basically, I

• started the superNode(ubuntu 20) on AWS
• on the superNode, started a edge and join itself
• set up DHCP on the targeted network interface on my superNode
• DHCP server log showed that it was active
• join the superNode on another machine(debian buster, raspberry pi), using -a dhcp:0.0.0.0

Result:
DHCP didn't assign any ip on my edge

~$ ip a

5: A5TAP: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1290 qdisc pfifo_fast state UNKNOWN group default qlen 1000
    link/ether ce:be:21:a5:35:da brd ff:ff:ff:ff:ff:ff
    inet6 fe80::ccbe:21ff:fea5:35da/64 scope link 
       valid_lft forever preferred_lft forever

Anything I did wrong to setup DHCP on n2n?

[Logan007]

I never tried DHCP at large scale, so I am a bit guessing here. But doesn't DHCP setup usually also require a DHCP client such as dhpcd?

As far as I can see, n2n itself does not include a DHCP client portion. By giving the dhcp: prefix and -r, n2n only paves the way to handle DHCP protocol on the line.

P. S. You could try the integrated auto IP address feature as of current 2.9 – you will not find it in 2.8; but keep in mind that it is still developing dev branch.

[maaarcus]

Thank you so much @Logan007 . You filled my missing puzzle and it worked... but not entirely...

So I once again joined my superNode on my pi:
sudo edge -r -d A5TAP -c a5 -k mykey -a dhcp:0.0.0.0 -l my-super-node-ip:1234

You mentioned I need to setup my client side dhcp. I found that I need to define the A5TAP interface, and set it to use dhcp.
so I went to /etc/network/interfaces on my edge and added:

auto  A5TAP
iface A5TAP inet dhcp

then I did :
sudo systemctl restart networking

and then I can see my edge has its ip assigned by my DHCP server!

ip a

4: A5TAP: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1290 qdisc pfifo_fast state UNKNOWN group default qlen 1000
    link/ether 02:8c:4c:9b:d4:67 brd ff:ff:ff:ff:ff:ff
    inet 192.168.233.2/24 brd 192.168.233.255 scope global dynamic A5TAP
       valid_lft 505sec preferred_lft 505sec
    inet6 fe80::8c:4cff:fe9b:d467/64 scope link 
       valid_lft forever preferred_lft forever

---

However, if I have the below setting on /etc/network/interfaces before A5TAP was available, I will not be able to reach the Internet at all. I have to add it after I've connected to the superNode, and then restart the network in order for it to work. Any ideas on how should I handle this? Seems like if the interface A5TAP is not created and I defined it in the config file, the network breaks.

auto  A5TAP
iface A5TAP inet dhcp

My /etc/network/interfaces FYR:

source-directory /etc/network/interfaces.d

auto wlan0
iface wlan0 inet dhcp
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet dhcp

#auto  A5TAP <- if added before A5TAP is created, cannot reach the Internet
#iface A5TAP inet dhcp

[Logan007]

I hope there is a way to have DHCP client working on a specified interface only. Arch Wiki shows how to start dhcpcd service on a specific interface only, so you could first start the edge (which creates the interface) and then start the dhcpcd service on that interface (only) afterwards; hints are that command line /usr/bin/dhcpcd -w -t 0 <interface> might do as well.

If you run edge as a service, ExecStartPost might come in handy. Perhaps, as the involved dhcpcd itself is a service, there might be a solution involving the Wants/Requires/Befire/After/... entries in the .service file.

Can anyone with a working DHCP-over-n2n setup provide more details?

[maaarcus]

I played around a bit and found a solution that is working potentially:

I changed the line:
auto A5TAP
to
allow-hotplug A5TAP

After this, it won't block my pi from accessing the Internet on reboot, or when A5TAP interface has not been created yet. I can run the edge command at any point, and I will get my dhcp ip.

Please let me know if we have better approaches.

Thank you again @Logan007. I was stuck for so long!

[Logan007]

Thank you for bringing this up. I might add it to our documentation.