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My network topology:

                            mac
                        192.168.1.4
                             |
internet - netcom 192.168.1.1-192.168.1.253 linux 192.168.2.1-192.168.2.2 windows
  • netcom is NAT gateway to internet
  • netcom has a static route to 192.168.2.0/24 via 192.168.1.253
  • mac has a static route to 192.168.2.0/24 via 192.168.1.253
  • mac has a default gw of 192.168.1.1
  • linux has default gw of 192.168.1.1
  • linux has port forwarding and disabled firewall
  • windows has a default gw of 192.168.2.1
  • mac can ping windows, linux, and netcom
  • linux can ping windows, mac, and netcom
  • windows can ping mac and linux BUT NOT netcom
  • netcom can ping mac and linux BUT NOT windows

lastly, i ran tcpdump while trying to ping netcom from windows (and vice versa) and it shows packets are going through the correct interfaces, any idea what could be wrong?

ping from netcom to windows shows the following logs:

ping in netcom:

 > ping 192.168.2.2
app: echo 1 > /var/ping_dns_status
PING 192.168.2.2 (192.168.2.2): 56 data bytes

--- 192.168.2.2 ping statistics ---
4 packets transmitted, 0 packets received, 100% packet loss

tcpdump in linux:

00:03:12.441283  In 18:f1:45:75:2c:24 ethertype IPv4 (0x0800), length 100: 192.168.1.1 > 192.168.2.2: ICMP echo request, id 5784, seq 0, length 64
00:03:12.441341 Out 00:0c:29:0b:03:c3 ethertype IPv4 (0x0800), length 100: 192.168.1.1 > 192.168.2.2: ICMP echo request, id 5784, seq 0, length 64
00:03:12.441829  In 00:0c:29:e9:17:84 ethertype IPv4 (0x0800), length 100: 192.168.2.2 > 192.168.1.1: ICMP echo reply, id 5784, seq 0, length 64
00:03:12.441850 Out 00:0c:29:0b:03:b9 ethertype IPv4 (0x0800), length 100: 192.168.2.2 > 192.168.1.1: ICMP echo reply, id 5784, seq 0, length 64

wireshark on windows:

192.168.1.1     192.168.2.2     ICMP    98      Echo (ping) request  id=0x1698, seq=0/0, ttl=63 (reply in 2548)
192.168.2.2     192.168.1.1     ICMP    98      Echo (ping) reply    id=0x1698, seq=0/0, ttl=128 (request in 2547)
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    Does tcpdump on Windows (or Wireshark) show that it is receiving the ping packets from netcom? (And is it trying to reply?)
    – u1686_grawity
    Aug 23, 2019 at 7:36
  • @grawity i've added the logs in netcom (ping) linux (tcpdump) and windows (wireshark)
    – stratjunkie
    Aug 23, 2019 at 12:09
  • Does the netcomm has firewall enabled?
    – Chan Tzish
    Aug 23, 2019 at 12:16
  • @ChanTzish, don't know how to check that, the netcomm has a very minimal (probably linux) os, and not even sure if it has firewall commands built in
    – stratjunkie
    Aug 23, 2019 at 12:19
  • @ChanTzish ok, i tried iptables -L and it shows a lot of rules, not sure which one in particular could be dropping my packets
    – stratjunkie
    Aug 23, 2019 at 12:21

1 Answer 1

Reset to default
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on linux machine packet forwarding is disabled by default. Try to run commands:

iptables -A FORWARD -i eth1 -j ACCEPT

iptables -A FORWARD -o eth1 -j ACCEPT

(and same two commands on another network interfaces instead of eth1)

sysctl -w net.ipv4.ip_forward=1

and add to /etc/sysctl.conf

net.ipv4.ip_forward = 0

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  • firewall is disabled in linux and forwarding is enabled that's why mac can ping windows
    – stratjunkie
    Aug 23, 2019 at 11:47

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