For applications that are aware of network namespaces, the convention is
       to look for global network configuration files first in /etc/netns/NAME/
       then in /etc/.  For example, if you want a different version of
       /etc/resolv.conf for a network namespace used to isolate your vpn you
       would name it /etc/netns/myvpn/resolv.conf.

       ip netns exec automates handling of this configuration, file convention
       for network namespace unaware applications, by creating a mount namespace
       and bind mounting all of the per network namespace configure files into
       their traditional location in /etc.