Tag Archives: network

Aug 16

Network traffic sniffing: tcpdump on Linux + Wireshark on Windows

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Reading time: 2 – 2 minutes

From the Windows box using the CLI console (cmd):

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 removed
C:\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 -

Jul 12

Windows 10: Internal Virtual Switch with NAT

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Reading time: 2 – 4 minutes

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.

Using PowerShell the steps are:

New-VMSwitch -SwitchName NATSwitch -SwitchType Internal
New-NetIPAddress -IPAddress 10.46.1.1 -PrefixLength 24 -InterfaceAlias "vEthernet (NATSwitch)"
New-NetNAT -Name NATNetwork -InternalIPInterfaceAddressPrefix 10.46.1.0/24

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.

Running the commands looks like:

For removing what you did:

Remove-VMSwitch -Name "NATSwitch"
Remove-NetIPAddress -InterfaceAlias "vEthernet (NATSwitch)"
Remove-NetNAT -Name NATNetwork

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.

Jul 07

rp_filter Linux kernel feature

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Reading time: 1 – 2 minutes

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:

root@mini9:/proc/sys/net/ipv4# cat ./conf/all/rp_filter
1
root@mini9:/proc/sys/net/ipv4# cat ./conf/ztly5q4n37/rp_filter
1

May 27

DRY DHCP Client: request and IP address to the DHCP server without a DHCP Client

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Reading time: < 1 minute

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-discover

Starting Nmap 7.60 ( https://nmap.org ) at 2021-05-19 15:07 CEST
Pre-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, 8.8.4.4
WARNING: No targets were specified, so 0 hosts scanned.
Nmap done: 0 IP addresses (0 hosts up) scanned in 1.43 seconds

Jul 06

URL shortener service: https://url.joor.net (pygmy)

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Reading time: 2 – 2 minutes

Lately, I started running my own URL shortener service because of Google URL shortener service is going to shut down. Below there is a short video showing how the service runs and also there is a Google Chrome extension which I created for integrating the service with the browser.

For quick access and reference the URLs are:

Final notes:

  • Base URL is not the shortest one, but for my personal requirements, it’s more than enough.
  • Service is in early stages, especially the extension. Expect errors, bugs, and unavailabilities.
  • Service is open and free for everyone. But remember, the main purpose is my personal use.
  • I know that pygmy has more features than I publish but I don’t need them and I don’t want to maintain those parts of the applications.
  • I appreciate the effort of Amit for so good application.

May 02

HTTPie – command line HTTP client

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Reading time: 1 – 2 minutes

I imagine you are used to using curl for many command line scripts, tests, and much more things. I did the same but some weeks ago I discovered HTTPie which is the best substitute that I’ve ever found for curl. Of course, it’s also available for a lot of Linux distributions, Windows, and Mac. But I used it with docker which is much more transparent for the operative system and easy to update. To be more precise I use next alias trick for using this tool:

alias http='sudo docker run -it --rm --net=host clue/httpie'

Official website: httpie.org

Let me paste some highlights about HTTPie:

  • Sensible defaults
  • Expressive and intuitive command syntax
  • Colorized and formatted terminal output
  • Built-in JSON support
  • Persistent sessions
  • Forms and file uploads
  • HTTPS, proxies, and authentication support
  • Support for arbitrary request data and headers
  • Wget-like downloads
  • Extensions
  • Linux, macOS, and Windows support

From the tool webpage a nice comparison about how HTTPie looks like versus curl.

Mar 07

socat tip: create virtual serial port and link it to TCP

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Reading time: < 1 minute Create a virtual serial port and publish it on TCP port: 

socat pty,link=/dev/virtualcom0,rawer tcp-listen:2101

In another computer, for instance, another virtual port can be created and connected to the previous one:

socat pty,link=/dev/virtualcom0,rawer tcp:SERVER_IP:2101

If in any of those both sides we want to open a real serial port, for instance, in the server case we can run:

socat /dev/ttyS0,rawer tcp-listen:2101

More information on socat manpage.

Jan 24

ngrok – service which solve services behind NAT issues

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Reading time: < 1 minute This is another short entry, in this case for recommending a service which we solve typical problem solved using a DNAT. Once we have a service on our laptop, or on a private server and we have to expose that service on the internet for some time or permanently usually we have to go the firewall, or router and create a NAT rule forwarding a port. This is a simple and powerful service which is going to solve that for you. There is a free account for understanding and testing the service, other plans are available and especially affordable for professional requirements.

ngrock.com

I was frogetting to say it’s compatible with Linux, Windows and Mac.