How to gain access into /etc/networks/loopback file from terminal? In the terminal I am typing:

sudo vi /etc/networks/loopback 
, but I am getting a permission denied inside the vi editor.

The /etc/networks file has this inside:

##
# Networks Database
##
loopback    127    loopback-net




Are those three items actual files I can go into?



I am running El Capitan Version 10.11.6.

Thank you.

Edit: I rebooted into recovery mode, typed in csrutil disable, and now when I type in sudo vi /etc/network/loopback I get this output:

E575: viminfo: Illegal starting char in line: /private/etc/networks
E575: viminfo: Illegal starting char in line: ^I"^I1^I0 
Press ENTER or type command to continue 


Then when I press enter, it goes into the vi editor but it still says [permission denied] on the bottom.
/etc/networks is not a folder, it's a plain text file with the contents given in your question.

loopback, 127 and loopback-net are not files within a file, they're just words within the contents of the /etc/networks file, as part of the configuration expressed within. There's no /etc/networks/loopback, as it's just the file /etc/networks with the word loopback within.