CDP device discovery in python

Today, I wrote a small python script to discover Ubiquiti Nanostation devices on the network using pacpy and dpkt. Since it is listening CDP packets, I guess it can also discover other kinds of devices, though not tested.

Limiting the active users/sessions in freeRADIUS

Here is how to limit the number of concurrent users/sessions in freeRADIUS. Let's say, you want to reject auth requests if there are already more than 50 active accounting sessions.

1. Add the following policy in your policy.conf
   

maximum_active_users = 50

check_active_users {
    if ("%{sql: SELECT COUNT (*) FROM  radacct WHERE acctstoptime IS NULL}" >= "%{config:policy.maximum_active_users}") {
        update reply {
             Reply-Message := "Too many users logged into the system. Please try again later."
        }
        reject
    }
}

2. Add check_active_users policy in your sites-enabled/default auth section.
   
   
3. Test it using radclient.
   
   

root @ ~ $ echo "User-Name=t1,User-Password=1234"  | radclient -x -d /etc/freeradius/ 192.168.100.108 auth testing123
Sending Access-Request of id 124 to 192.168.100.108 port 1812
        User-Name = "t1"
        User-Password = "1234"
rad_recv: Access-Reject packet from host 192.168.100.108 port 1812, id=124, length=84
        Reply-Message = "Too many users logged into the system. Please try again later."

Simple Data Compression Algorithms in Common Lisp

Common Lisp implementation of some data compression algorithms — Run-Length, Huffman, and Shannon–Fano Encodings — that I have written during my graduate course "Data Compression".

Internet connection sharing using iptables

Scenario ― I have several virtualbox GUEST machines, using an internal network on my PC. Now, I wanted to share host machine's internet connection to guest machines. I searched on the web how to do it using iptables. Most of the solutions seem too complex. Here is a working simple solution (found on centos documentation)

On Host Machine — type these commands in Terminal.

thura @ ~ $ sudo iptables -A FORWARD -i vboxnet0 -j ACCEPT
thura @ ~ $ sudo iptables -A FORWARD -o eth1 -j ACCEPT
thura @ ~ $ sudo iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

That's it. Now you can access the external network of host machine from guest machines. To access Internet, you may need to edit /etc/resolve.conf in your guest machine.

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 8.8.8.8

if_nametoindex, if_indextoname functions for python using ctypes

I needed to use if_nametoindex, if_indextoname functions for one of my packet capturing programs. So, here is my python wrapper for those functions using ctypes.


PS: You will need this only for python2.x. Those functions are available in socket module starting since python 3.3.