[python] Building and installing python3.x with python2.x in Linux

RHEL 6.x doesn't comes with python3. So if any of your project require python3 and also some of the projects need python2 then you may need those 2 version same time in your system.

Prerequisite:
gcc (C89)/g++
ld
ranlib


How:
1. Download python3.x package from https://www.python.org/downloads/release/python-343/
2. Extract it and move inside the package python-3.4.3
$ cd /python-3.4.3
3. Open a console and run the following configure command. We will build python with shared library support as many of the other project will require python3 dynamic library linking.

so, configure it by,
$ ./configure --prefix=/opt/python3 --enable-shared

We are putting build output directory as /opt/python3.

4. After completion now build it by,

$ make
 5. Then install it by alternate installation by,
$ make altinstall

6. Now create a symlink of the newly created python3 binary and copy the shared library to the /lib64/ directory of filesystem.
$ ln -s /opt/python3/bin/python3.4 /usr/bin/python3
$ cp /opt/python3/libpython3.* /lib64/
7.  Now run python script by,
 $ python3 my.py
And your python2 is also ok and usable!


[IPv6] Various address reachability scope on IPv6 network

IPv6 comes with various IP address terminology which can be assign to a system. Lets simply clarify their name and scope of reachability respect to IPv6. 


 In general it has four address type one of which is depreciated by RFC standard.

1. Link Local Address (LLA)
Description: Link-local address can be access in directly connected router. Its basically same as IPv4 private address. 
 
2. Unique Local Address (ULA)
Description:Unique Local Address(ULA), they will often be advertised by IPv6 home gateways for subscriber local use only, and won't be reachable anywhere outside the home. Unique Local Address (ULA), which is an address that is used for local communication in a site – within a company, within a campus or within a set of networks in branch offices.

3. Site Local Address
Description: Deprecated.

4. Global Unicast Address
Description: Global unicast address is basically reachable from anywhere in internet. IPv6 unicast global addresses are similar to IPv4 public addresses.