access public network with laptop -> ethernet -> nxpBoard -> 5GModem -> public network

louloulou · 05-03-2021, 11:32 AM

Hello,

I have a nxpBoard which has a 5GModem and an ethernet port. This nxpBoard can connect to the public network through the 5gModem.

I connect a laptop to the ethernet port of the nxpBoard and I would like to have access to the public network, on the laptop.
summary:
laptop -> ethernet -> nxpBoard -> 5GModem -> public network

The nxpboard has two interface eth0:192.168.1.1 and 5Gmoden (wwan:100.104.102.249)
The laptop has one interface (eth)enp5s0:192.168.1.2

the nxpobard can ping www.google.com and the laptop
the laptop can ping the nxpboard but cannot ping www.google.com

I don't understand what I'm missing. Bellow is my configuration.

Thank you,

On nxpboard
# ifconfig

Code:

eth0      Link encap:Ethernet  HWaddr 00:04:9F:06:EF:C6  
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::204:9fff:fe06:efc6/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:38 errors:0 dropped:0 overruns:0 frame:0
          TX packets:42 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:3328 (3.2 KiB)  TX bytes:3124 (3.0 KiB)

wwan0     Link encap:Ethernet  HWaddr EE:11:9D:37:87:28  
          inet addr:100.104.102.249  Bcast:0.0.0.0  Mask:255.255.255.252
          inet6 addr: fe80::ec11:9dff:fe37:8728/64 Scope:Link
          UP BROADCAST RUNNING NOARP MULTICAST  MTU:1428  Metric:1
          RX packets:21 errors:0 dropped:0 overruns:0 frame:0
          TX packets:43 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:1849 (1.8 KiB)  TX bytes:2982 (2.9 KiB)

# route

Code:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         100.104.102.250 0.0.0.0         UG    0      0        0 wwan0
8.8.8.0         100.104.102.250 255.255.255.0   UG    0      0        0 wwan0
100.104.102.248 *               255.255.255.252 U     0      0        0 wwan0
192.168.1.0     *               255.255.255.0   U     0      0        0 eth0

# iptables -L -v

Code:

Chain INPUT (policy ACCEPT 36 packets, 3180 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
   11   756 ACCEPT     all  --  eth0   wwan0   anywhere             anywhere            
    1    60 ACCEPT     all  --  wwan0  eth0    anywhere             anywhere             state RELATED,ESTABLISHED

Chain OUTPUT (policy ACCEPT 42 packets, 3392 bytes)
 pkts bytes target     prot opt in     out     source               destination

On the Laptop

laptop-GE66:~$ ifconfig

Code:

enp5s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.2  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 fe80::6261:6c92:3e99:20ae  prefixlen 64  scopeid 0x20<link>
        ether 2c:f0:5d:b5:a4:30  txqueuelen 1000  (Ethernet)
        RX packets 28  bytes 2264 (2.2 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 301  bytes 25115 (25.1 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device memory 0xa1200000-a12fffff

laptop-GE66:~$ route -n

Code:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.1     0.0.0.0         UG    20100  0        0 enp5s0
10.45.0.0       0.0.0.0         255.255.0.0     U     0      0        0 ogstun
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 ogstun
192.168.1.0     0.0.0.0         255.255.255.0   U     100    0        0 enp5s0

TenTenths · 05-04-2021, 03:48 AM

You're not NATing the laptop traffic, go read up about NAT / MASQUERADE

louloulou · 05-04-2021, 11:12 AM

Thank you, yes I needed to look MASQUERADE, it is working now but only for ip address not for domain name. Here is how I configured eth0 and wwan0 :

Code:

#!/bin/sh
ifconfig eth0 192.168.1.1
iptables -F
echo 1 > /proc/sys/net/ipv4/ip_forward
MODEM="wwan0"
ETH="eth0"
iptables -t nat -A POSTROUTING -o $MODEM -j MASQUERADE
iptables -t nat -A POSTROUTING -o $ETH -j MASQUERADE
iptables -A FORWARD -i $ETH -o $MODEM  -j ACCEPT
iptables -A FORWARD -i $MODEM -o $ETH -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -L -v

On the nxpboard I have a custom linux build with buildroot, I added dnsmasq to solve the domain name, I'm working on it.