Cannot get internet from pizero connected to pi3 via USB (eth0 to usb0)

Question

I cannot get internet access from a pizero connected via USB to a pi3 connected via ethernet.

        usb0 +---+
                 |
                 |
                 |
+------+    +---+|   +------+
|ROUTER+----+PI3+v---+PIZERO|
+------+    +---+    +------+
          +-^
          |
          +
         eth0

I tried to compile info from these articles to get where I am:

• http://blog.gbaman.info/?p=791#comment-136183
• http://raspberryjamberlin.de/zero360-part-2-connecting-via-otg-a-cluster-of-raspberry-pi-zeros-to-a-pi-3/
• Sharing the Pi's WiFi connection through the Ethernet port

pi3 and piZero are running Raspbian Jessie Lite 2017-01-11. The Pi Zero was setup for headless OTG with the method described here: https://gist.github.com/gbaman/975e2db164b3ca2b51ae11e45e8fd40a#file-howtootgfast-md

I now have:

1 - pi3 configured with static ips (able to reach internet)

pi3 :: /etc/dhcpcd.conf

[...]
nohook lookup-hostname

# Static IP for ethernet access
interface eth0
static ip_address=192.168.178.77/24
static routers=192.168.178.1
static domain_name_servers=192.168.178.1

# Subnet for usb0 (where the piZero is plugged)
interface usb0
static ip_address=10.0.11.1/24

2 - pi3 able to do ipv4 fwd

pi3 :: /etc/sysctl.conf

[...]
net.ipv4.ip_forward=1
[...]

3 - pi3 firewall set up to allow eth0 / usb0 communication

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE  
sudo iptables -A FORWARD -i eth0 -o usb0 -m state --state RELATED,ESTABLISHED -j ACCEPT  
sudo iptables -A FORWARD -i usb0 -o eth0 -j ACCEPT  

The output of the rules has been saved into a file automatically loaded by rc.local. This is the result of iptable-save after each reboot:

# Generated by iptables-save v1.4.21 on Mon Feb 13 12:01:27 2017

*nat
:PREROUTING ACCEPT [30:2521]
:INPUT ACCEPT [24:2233]
:OUTPUT ACCEPT [30:2616]
:POSTROUTING ACCEPT [19:1581]
-A POSTROUTING -o eth0 -j SNAT --to-source 192.168.178.77
-A POSTROUTING -o eth0 -j SNAT --to-source 192.168.178.77
-A POSTROUTING -o eth0 -j MASQUERADE
COMMIT
# Completed on Mon Feb 13 12:01:27 2017
# Generated by iptables-save v1.4.21 on Mon Feb 13 12:01:27 2017
*filter
:INPUT ACCEPT [339:38929]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [293:33013]
-A FORWARD -i usb0 -o eth0 -j ACCEPT
-A FORWARD -i eth0 -o usb0 -m state --state RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -i eth0 -o usb0 -m state --state RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -i usb0 -o eth0 -j ACCEPT
COMMIT
# Completed on Mon Feb 13 12:01:27 2017

4 - piZero configured with static ips (reachable from pi3 with ssh [email protected] and ssh [email protected])

piZero :: /etc/dhcpcd.conf

[...]
interface usb0
static ip_address=10.0.11.2
static routers=10.0.11.1
static domain_name_servers=10.0.11.1

Pinging 8.8.8.8 is successful on the PiZero:

$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=55 time=5.43 ms
[...]
--- 8.8.8.8 ping statistics ---
6 packets transmitted, 6 received, 0% packet loss, time 5006ms
rtt min/avg/max/mdev = 4.659/4.850/5.435/0.279 ms

But still no access to internet from the PiZero (impossible to ping stackexchange.com or to run apt-get update). Any ideas?

Answer 1

Did you try to ping 8.8.8.8 from the Zero? You told the piZero to use 10.0.11.1 as DNS, but maybe the RPi3 has none setup.

Did you also reboot the RPi3 after enabling ipv4 forward?

Are the iptables rules on the RPi3 still there? (could be that were lost during the the reboot if no persistency is enabled :))

EDIT: After seeing that @xav could ping 8.8.8.8 from piZero, it was proven that Internet Connectivity was there, however no DNS resolution. This was fixed by adding an public DNS server to the network config of the piZero:

piZero :: /etc/dhcpcd.conf
[...]
interface usb0
static ip_address=10.0.11.2
static routers=10.0.11.1
static domain_name_servers=8.8.8.8

After an reboot of the piZero, it worked.

However, the piZero is not reachable from the main network 192.168.178.x due to the fact that the pcs in the main network do not know of the route to the piZero via the RPi3