We have Docker running with containers that are connected to their own private network. To efficiently manage and monitor these containers, it’s often useful to retrieve their private IP addresses.
With the following command, you can easily obtain the private IP addresses of all running Docker containers:
Assume that we have a service only available in localhost (127.0.0.1/8) and we want to expose this port temporarily. Of course, you can use iptables for redirecting the port. But take care, this is not a simple DNAT because packets will not be evaluated by PREROUTING (-t nat) rules.
Another option is using an old-powerful Swiss knife tool: socat (github) (my fork).
# binds public port to any local interfacesocat TCP-LISTEN:<public_port>,fork TCP:127.0.0.1:<internal_port># binds only to an IP addressSOCAT_SOCKADDR=<interface_IP> socat TCP-LISTEN:<public_port>,fork TCP:127.0.0.1:<internal_port># examples:# binds to all interfaces:socat TCP-LISTEN:1880,fork TCP:127.0.0.1:1880# just for an IP address of one interface:SOCAT_SOCKADDR=10.2.0.110 socat TCP-LISTEN:1880,fork TCP:127.0.0.1:1880
ssh USER@HOST "tcpdump -s 0 -U -n -w - -i NETIF FILTER"|"c:\Program Files\Wireshark\Wireshark.exe"-k -i -# USER - remote user of the linux box# HOST - host address of the remote linux box# NETIF - network interface to snif in the remote linux box# FILTER - (optional) rules for filtering traffic to capture
Use case:
C:\Windows\System32\OpenSSH>ssh root@192.168.4.74 "tcpdump -s 0 -U -n -w - -i eno2 udp and not port 53" | "c:\Program Files\Wireshark\Wireshark.exe" -k -i -
Let me present a rare use case of this useful trick. I use a QNAP NAS as a gateway in my home network, where I have 5 NICs. So it’s really useful to snif traffic remotly but I have no tcpdump packet in the system. What I did is use tcpdump as Docker container and finally the commands is like that.
# sniffing SIP traffic (port 5060) on interface eth0# remote linux host (QNAP NAS) use SSH port 55222# docker container is created and when work is done is removedC:\Windows\System32\OpenSSH>ssh -p 55222 admin@10.2.0.1 "cd /share/Container/tcpdump && docker run --rm --net=host corfr/tcpdump -s 0 -U -n -w - -i eth0 not port 22 and port 5060" | "c:\Program Files\Wireshark\Wireshark.exe" -k -i -
When you are playing with Windows Hyper-V and you want to create a completely virtual internal network with private virtual machines inside your Windows 10 machine virtual switch are mandatory.
Then it’s the time to connect that virtual switch with the host machine using a virtual network interface. All those steps can be done using Hyper-V manager user interface, but you cannot control 100% of parameters like enable, or not, the NAT of the virtual internal network.
Of course, change “NATSwitch” for your switch name and “10.46.1.1” for the IP address of the host virtual network card. Finally “NATNetwork” is another arbitrary name for referring to the NAT rule, and “10.46.1.0/24” is the network address of the virtual internal host network.
In Windows 10 IP forwarding is not enabled and packets between interfaces are not routed. According to the Microsoft forums, you can enable IP forwarding (routing) using the following steps:
Go to Start and search on cmd or command. Right click on either cmd or command then select Run as administrator. At the command prompt type regedit. Navigate to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\ Services\Tcpip\Parameters\IPEnableRouter setting, right click and select Modify. Change 0 to 1 and exit the editor.
When your back at the command prompt type services.msc and navigate to the Routing and Remote Access service. Right click and select Properties. Change to Automatic and click on Start to start the service.
I had to research a long time until I found all this information, but in my case leverage my proofs of concepts to another level.
It’s just an IP spoofing protection which is by default enabled on Linux kernels. When it’s value is ‘1’ means that all IP address which are not directly routable and received form a network interface they are directly discarded.
So, if you want to scan a range of IP address in your LAN which not belong to that interface address space when packets from IP addresses are received they are going to be discarded by the kernel. So, take that into account when you have those “unusual” requirements.
It can be enable/disabled by all interfaces or just one:
When you want to discover LAN metadata without being part of that network. So, when you want to discover network address range, gateway, DNS IPs, DHCP server IPs, etc. this simple nmap parameter will help you so much.
# nmap --script broadcast-dhcp-discoverStarting Nmap 7.60( https://nmap.org ) at 2021-05-1915:07 CESTPre-scan script results:| broadcast-dhcp-discover:| Response 1 of 1:| IP Offered:192.168.1.127| DHCP Message Type: DHCPOFFER| Subnet Mask:255.255.255.0| Renewal Time Value:4d00h00m00s| Rebinding Time Value:7d00h00m00s| IP Address Lease Time:8d00h00m00s| Server Identifier:192.168.1.1| Router:192.168.1.1|_ Domain Name Server:8.8.8.8,8.8.4.4WARNING: No targets were specified, so 0 hosts scanned.Nmap done:0 IP addresses(0 hosts up) scanned in1.43 seconds
