May 02

HTTPie – command line HTTP client

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

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

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.

Jan 19

DHCP server for Windows 10

Reading time: 1 – 2 minutes

This is a super useful and simple tool, first of all, let me say thanks to Dani because I found the tool thanks to him. Very often I have the requirement to set up small virtual, real or hybrid networks using my laptop as a server and I had to boot a VM for getting a DHCP server simple to manage and powerful. Now, this is not required anymore because thanks to this tool I found a super small and flexible tool, I can set up all that I need using an INI file or just a wizard. It’s a pleasure and I don’t have to install anything if I don’t want, just a tray icon application is running for allowing me to give the service to my experimental networks.

Those projects that gain my commitment in a second: DHCP Server for Windows

Sep 19

Restricted user for SSH port forwarding

Reading time: 2 – 2 minutes

I love “ssh -R” reverse SSH is really useful when you have to get access to a Linux machine behind a NAT or firewall. One of the most powerful scenarios to get that running is use a third machine with a public IP address. The idea will be run reverse SSH command in target Linux and publish a forward port at the third server, so you only have to connect to a published port in that third server and you’ll get the target Linux thanks to the reverse SSH connection open between them.

reverse-ssh-schema

A long time ago I talked about that in my podcast “2×04 SSH avançat“.

With this scenario we have a security challenge with the SSH user account on the “third server”, we want a secure user:

  • without shell and sftp access
  • secure enough to only allow port forwarding features
  • access only allowed with authorized keys

I’m not going to give precise Linux instructions on that limited user, but for user you’re not going to have problems to get that:

/etc/passwd(-):

limited-user:x:1001:1001::/home/limited-user:

/etc/shadow(-):

limited-user:!:17037:0:99999:7:::

/etc/ssh/sshd_config:

Match User limited-user
    GatewayPorts yes
    ForceCommand echo 'This account can only be used for maintenance purposes'

Of course, you’ll have your own UID, GID and use your own username. And at “/home/limite-user/.ssh/authorized_ssh” you’ll have to pub public key of the clients that want to use the service.

I’ve got my inspiration to get that from: How to create a restricted SSH user for port forwarding?. Thank you askubnutu.com.

Sep 05

Cookbook: set-up a TFTP server on Ubuntu

Reading time: 1 – 2 minutes

Sometimes TFTP is the only protocol available to exchange files with an embedded system. So, it’s very easy to have that supported in our workstation or any other place to exchange files with those systems.

Set up steps:

apt-get install tftpd-hpa

modify file “/etc/default/tftpd-hpa”:

TFTP_OPTIONS="--secure --create"

–secure: Change root directory on startup. This means the remote host does not need to pass along the directory as part of the transfer, and may add security. When –secure is specified, exactly one directory should be specified on the command line. The use of this option is recommended for security as well as compatibility with some boot ROMs which cannot be easily made to include a directory name in its request.

–create Allow new files to be created. By default, tftpd will only allow upload of files that already exist. Files are created with default permissions allowing anyone to read or write them, unless the –permissive or –umask options are specified.

Needed to allow uploads in that directory:

chown -R tftp /var/lib/tftpboot

Restart and check if the service is running:

service tftpd-hpa restart
service tftpd-hpa status
netstat -a | grep tftp
Sep 01

New home server working as a wifi AP and DHCP server

Reading time: 2 – 3 minutes

At the beginning of August I’ve received a new home server, I decided to stop my old HP ML110 G5 and substitute that by a new silent and low power server also based on Intel technologies in this case it’s al i5 with 8G of RAM and 128GB of SSD for less than 300€ including custom costs I think it’s a very good investment.

fmp03-geekbuing

 

I installed Ubuntu 16.04 LTS server, I don’t tried de Win10 pre-installed. I happy to see a very new and powerful BIOS with tons of options. But in this blog entry I want to explain how to set-up the wifi card as a wifi AP. I didn’t have to do anything to configure the card. It worked by default.

Ralink corp. RT3090 Wireless 802.11n 1T/1R PCIe

The first thing is check if the wifi network is compatible with the AP mode.

iw list
...
Supported interface modes:
         * IBSS
         * managed
         * AP
         * AP/VLAN
         * monitor
         * mesh point
...

Next thing is install the “hostapd” which is going to take care to set-up the AP. The configuration file have to be something like that “/etc/hostapd/hostpad.conf

interface=wlan0   # change that with the wifi interface name
driver=nl80211
ssid=test         # your wifi network name
hw_mode=g
channel=1         # look up for a free channel
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=3
wpa_passphrase=1234567890   # passwor to join the wifi network
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

Modify “/etc/default/hostapd” and put that:

DAEMON_CONF="/etc/hostapd/hostapd.conf"

Start the hostapd service:

sudo service hostapd start

Now the AP is running but a DHCP service giving IPs it’s need, I used “isc-dhcp-server”. First thing to configure is “/etc/default/isc-dhcp-server” with the wireless network name:

INTERFACES="wlan0"

Next file to be configured is “/etc/dhcp/dhcpd.conf”:

ddns-update-style none;
log-facility local7;

subnet 192.168.1.0 netmask 255.255.255.0 {
    range 192.168.1.128 192.168.1.253;
    option domain-name-servers 192.168.1.1;
    option routers 192.168.1.1;
}

Don’t forget to start the service:

sudo service isc-dhcp-server start

If it’s needed remember to create the proper iptables rules and enable “ip_forward” in /proc filesystem. I’m not going to describe that because in my case it’s not going to be useful.

This is not a specially interesting post entry but useful as a reference, when you have to use a fast and easy cookbook to setup a wifi AP.

Aug 29

Internet fail over connection with Mikrotik

Reading time: 2 – 4 minutes

Based on my home configuration I’m going to describe how to set up a Mikrotik to manage fail over Internet connection. Next schema describes a Mikrotik gateway with two internet connections (GUIFI and SS). Assuming GUIFI as a default Internet connection periodic checks on Google DNSes (8.8.8.8 and 8.8.4.4) will allow to know when it’s good to change the default route.
internet-failover

 

If you have some Linux routing background it will be easier to understand the configuration. Main idea is use policy routing tables and mark packets to use one table or other. In my case I have two routing tables GUIFI and SS, and of course, the default gateway of each of those tables is the gateway indicated in the schema.

First step is take care about the routes for hosts to monitor; using GUIFI connection will be checking connectivity to 8.8.8.8 and using SS the monitored host will be 8.8.4.4.

/ip route
add dst-address=8.8.8.8 gateway=172.29.2.1 scope=10
add dst-address=8.8.4.4 gateway=172.29.1.1 scope=10

Second step is configure two routing tables, those routes will check Internet hosts availability. Routes are resolved recursively (more info), and will be active only if any host is pingable.

# routing table for GUIFI
/ip route
add distance=1 gateway=8.8.8.8 routing-mark=GUIFI check-gateway=ping
add distance=2 gateway=8.8.4.4 routing-mark=GUIFI check-gateway=ping
# routing table for SS
/ip route
add distance=1 gateway=8.8.4.4 routing-mark=SS check-gateway=ping
add distance=2 gateway=8.8.8.8 routing-mark=SS check-gateway=ping

Routing table looks like that:

routing-table

Next step will be create marking rules in the firewall:

# next rule mark all LAN traffic (10.2.0.0/26) before routing
# it'll be processed by routing table GUIFI
# it makes GUIFI the default Internet connection 
/ip firewall mangle
add action=mark-routing chain=prerouting comment="All LAN traffic" dst-address=\
    !10.0.0.0/8 new-routing-mark=GUIFI passthrough=no src-address=10.2.0.0/26

If any specific host, service or whatever want to use specific routing table, then you can create new rules with proper mark to redirect the traffic to that Internet connection. But if that path fails other Internet connection will be used.

In my case I have a more complicated scenario, internal VoIP server uses a IP Telephony service only available through GUIFI connection. The way to force that is forbidding traffic to SS connection. A simple firewall rule will help to do that:

# X.X.X.X = IP address of the IP telephony provider
/ip firewall filter
add action=reject chain=forward dst-address=X.X.X.X in-interface=\
    bridge-lan out-interface=SS-eth2

I hope previous simple notes are useful for you, they are inspired by Advanced Routing Failover without Scripting.