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Question

Why

  $ ping ya.ru
 ping: unknown host ya.ru

Comp1 (host Internet)

  $ ifconfig wlan0
 wlan0 Link encap: Ethernet HWaddr b8: 03: 05: c9: 3e: c5  
           inet addr: 192.168.0.2 Bcast: 192.168.0.255 Mask: 255.255.255.0
           inet6 addr: fe80 :: ba03: 5ff: fec9: 3ec5 / 64 Scope: Link
           UP BROADCAST RUNNING MULTICAST MTU: 1500 Metric: 1
           RX packets: 33086 errors: 0 dropped: 0 overruns: 0 frame: 0
           TX packets: 62823 errors: 0 dropped: 0 overruns: 0 carrier: 0
           collisions: 0 txqueuelen: 1000 
           RX bytes: 2797459 (2.7 MB) TX bytes: 90723494 (90.7 MB)

и так делал

  $ ip route
 default via 192.168.0.  2 dev wlan0 scope link metric 100 
 192.168.0.0/24 dev wlan0 proto kernel scope link src 192.168.0.2 metric 9

and so did

  $ ip route
 default via 192.168.0.  1 dev wlan0 scope link metric 100 
 192.168.0.0/24 dev wlan0 proto kernel scope link src 192.168.0.2 metric 9

  $ sudo iptables-save
 : empty

  $ nslookup ya.ru
 ;;  connection timed out;  no servers could be reached

  $ ping 8.8.8.8
 connect: Network is unreachable

Comp2 (3g distributor)

  $ ifconfig -a
 eth0 Link encap: Ethernet HWaddr b8: 88: e3: 67: d4: 45  
           UP BROADCAST MULTICAST MTU: 1500 Metric: 1
           RX packets: 0 errors: 0 dropped: 0 overruns: 0 frame: 0
           TX packets: 0 errors: 0 dropped: 0 overruns: 0 carrier: 0
           collisions: 0 txqueuelen: 1000 
           RX bytes: 0 (0.0 B) TX bytes: 0 (0.0 B)

 lo Link encap: Local Loopback  
           inet addr: 127.0.0.1 Mask: 255.0.0.0
           inet6 addr: :: 1/128 Scope: Host
           UP LOOPBACK RUNNING MTU: 65536 Metric: 1
           RX packets: 5976 errors: 0 dropped: 0 overruns: 0 frame: 0
           TX packets: 5976 errors: 0 dropped: 0 overruns: 0 carrier: 0
           collisions: 0 txqueuelen: 0 
           RX bytes: 547759 (547.7 KB) TX bytes: 547759 (547.7 KB)

 ppp0 Link encap: Point-to-Point Protocol  
           inet addr: 10.225.20.196 PtP: 10.64.64.64 Mask: 255.255.255.255
           UP POINTOPOINT RUNNING NOARP MULTICAST MTU: 1500 Metric: 1
           RX packets: 14699 errors: 0 dropped: 0 overruns: 0 frame: 0
           TX packets: 13627 errors: 0 dropped: 0 overruns: 0 carrier: 0
           collisions: 0 txqueuelen: 3 
           RX bytes: 11287729 (11.2 MB) TX bytes: 2950024 (2.9 MB)

 wlan0 Link encap: Ethernet HWaddr 50: b7: c3: 2a: 68: 31  
           inet addr: 192.168.0.1 Bcast: 192.168.0.255 Mask: 255.255.255.0
           inet6 addr: fe80 :: 52b7: c3ff: fe2a: 6831/64 Scope: Link
           UP BROADCAST RUNNING MULTICAST MTU: 1500 Metric: 1
           RX packets: 1000 errors: 0 dropped: 0 overruns: 0 frame: 0
           TX packets: 1021 errors: 0 dropped: 0 overruns: 0 carrier: 0
           collisions: 0 txqueuelen: 1000 
           RX bytes: 148348 (148.3 KB) TX bytes: 108966 (108.9 KB)

 wwan0 Link encap: Ethernet HWaddr 58: 2c: 80: 13: 92: 63  
           BROADCAST MULTICAST MTU: 1500 Metric: 1
           RX packets: 0 errors: 0 dropped: 0 overruns: 0 frame: 0
           TX packets: 0 errors: 0 dropped: 0 overruns: 0 carrier: 0
           collisions: 0 txqueuelen: 1000 
           RX bytes: 0 (0.0 B) TX bytes: 0 (0.0 B)

  $ ip route
 default via 10.64.64.64 dev ppp0 metric 100 
 10.64.64.64 dev ppp0 proto kernel scope link src 10.225.20.196 
 192.168.0.0/24 dev wlan0 proto kernel scope link src 192.168.0.1 metric 9

  net.ipv4.ip_forward = 1

Even after the command:

  $ sudo iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -d 10.0.0.0/24 -o ppp0 -j MASQUERADE

iptables is empty

  $ sudo iptables -L -v -n --line
 Chain INPUT (ACCEPT 11498 packets, 8572K bytes)
 num pkts bytes target prot opt in out source destination         

 Chain FORWARD (policy ACCEPT 2 packets, 112 bytes)
 num pkts bytes target prot opt in out source destination         

 Chain OUTPUT (policy ACCEPT 11183 packets, 2394K bytes)
 num pkts bytes target prot opt in out source destination

  $ sudo iptables-save
 # Generated by iptables-save v1.4.21 on Fri Aug 12 21:04:53 2016
 * nat
 : PREROUTING ACCEPT [437: 43281]
 : INPUT ACCEPT [389: 28232]
 : OUTPUT ACCEPT [1207: 218579]
 : POSTROUTING ACCEPT [66: 9831]
 -A POSTROUTING -o ppp0 -j MASQUERADE
 COMMIT
 # Completed on Fri Aug 12 21:04:53 2016
 # Generated by iptables-save v1.4.21 on Fri Aug 12 21:04:53 2016
 * filter
 : INPUT ACCEPT [29340: 31886316]
 : FORWARD ACCEPT [0: 0]
 : OUTPUT ACCEPT [21601: 3071749]
 -A FORWARD -s 192.168.0.0/24 -i wlan0 -o ppp0 -j ACCEPT
 -A FORWARD -d 192.168.0.0/24 -i ppp0 -o wlan0 -j ACCEPT
 COMMIT
 # Completed on Fri Aug 12 21:04:53 2016

  $ nslookup ya.ru
 Server: 127.0.1.1
 Address: 127.0.1.1 # 53

 Non-authoritative answer:
 Name: ya.ru
 Address: 93.158.134.3
 Name: ya.ru
 Address: 213.180.193.3
 Name: ya.ru
 Address: 213.180.204.3

Made :

iptables -F
iptables -X
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
iptables -A FORWARD -i wlan0 -o ppp0 -s 192.168.0.0/24 -j ACCEPT
iptables -A FORWARD -i ppp0 -o wlan0 -d 192.168.0.0/24 -j ACCEPT

Received

  $ sudo iptables -t nat -nvL
 Chain PREROUTING (policy ACCEPT 72 packets, 4357 bytes)
  pkts bytes target prot opt in out source destination         

 Chain INPUT (policy ACCEPT 65 packets, 3965 bytes)
  pkts bytes target prot opt in out source destination         

 Chain OUTPUT (policy ACCEPT 88 packets, 13008 bytes)
  pkts bytes target prot opt in out source destination         

 Chain POSTROUTING (ACCEPT 5 packets, 890 bytes)
  pkts bytes target prot opt in out source destination         
    90 12510 MASQUERADE all - * ppp0 0.0.0.0/0 0.0.0.0/0

But the masquerade does not work.

As a result, on comp2 there is an Internet and ping comp1. And on comp1 there is no internet, although ping comp2. Why is there no internet? (

So, you add the rule to NAT mangle, but look at it completely wrong.
First, reset the current iptables -F rules iptables -F and iptables -X then add iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE then make sure that it was added iptables -t nat -nvL still probably would not put forward iptables -A FORWARD -i wlan0 -o ppp0 -s 192.168.0.0/24 -j ACCEPT and iptables -A FORWARD -i ppp0 -o wlan0 -d 192.168.0.0/24 -j ACCEPT
please attach the sudo iptables-save command output on both computers.
You can edit the question by clicking edit below the question text.
Well, now the task is more complicated: on "comp1" run ping 8.8.8.8 , and on "comp2" alternately, with an interval of 15 seconds, run tcpdump -ni wlan0 host 8.8.8.8 and tcpdump -ni ppp0 host 8.8.8.8 - you are somewhere should see traffic from "comp1" in consequence of which to determine at what stage packets are lost.

Answer 1 · 2016-08-12T08:10:03

since the /etc/resolv.conf file is not mentioned in the question, it is most likely the case.

This file stores information needed by the system to convert domain names to ip-addresses (and vice versa).

at least it should contain a line of the form:

 nameserver ip-адрес

where the ip-адрес is the address of the dns-server (name server) , which, in fact, will perform (when it is accessed by your system) the above-mentioned conversion (for example, ya.ru → 93.158.134.3 ).

the “closer” the name server is, the faster the response will be received from it. You can take the address from a similar file from a second computer. or use some public:

8.8.8.8 , 8.8.4.4 ( supported by google )
77.88.8.8 , 77.88.8.1 ( supported by yandex )

Computer with the Internet $ cat /etc/resolv.conf # Dynamic resolv.conf (5) file for glibc resolver (3) generated by resolvconf (8) # YOUR CHANGES WILL BE OVERWRITTEN nameserver 127.0. 1.1 ____________________ a computer without an Internet, he has only comments, there was no nameserver I tried to put 8.8.8.8, 192.168.0.1, 127.0.0.1 nothing.
so as not to fool yourself, feel free to put the address of any public dns-server (examples in the answer).
Well, this is the work of standards on a computer with an Internet, such an IP, I know what 127.0.0.0/24, 168.0.0.0/24, 10.0.0.0/24 is, I tried other IPs to enter it does not help.
and output of the $ cat /proc/sys/net/ipv4/ip_forward on the second computer.

vvv vvv 36 5 bronze marks · Accepted Answer · 2016-08-12T18:06:59

On both computers registered in the /etc/resolv.conf file

  nameserver 8.8.8.8

Thank you @ alexander-barakin

Made on computer2 (with 3g Internet):

iptables -F
iptables -X
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
iptables -A FORWARD -i wlan0 -o ppp0 -s 192.168.0.0/24 -j ACCEPT
iptables -A FORWARD -i ppp0 -o wlan0 -d 192.168.0.0/24 -j ACCEPT

Thank you @nobody

And earned. Thanks to all!)

of the five given commands, only a third is needed (and carries some meaning).

Distribute internet

Comp1 (host Internet)

Comp2 (3g distributor)

2 answers 2

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