Re: [gentoo-user] Why do we add the local host name to the 127.0.0.1 / ::1 entry in the /etc/hosts file?

[Michael]

On Wednesday, 10 March 2021 13:27:24 GMT Mark Knecht wrote:
> On Tue, Mar 9, 2021 at 10:10 PM Grant Taylor <
>
> gtaylor@×××××××××××××××××××××.net> wrote:
> > On 2/21/21 3:23 PM, Grant Taylor wrote:
> > > Will someone please explain why the Gentoo AMD64 Handbook ~> Gentoo (at
> > > large) says to add the local host name to the 127.0.0.1 (or ::1) entry
> > > in the /etc/hosts file?  What was the thought process behind that?
> >
> > Shameless Bump  --  I'm still interested in understanding the logic
> > behind the choice in the Gentoo Handbook.
> >
> > Additional information.
> >
> > The Samba Wiki states the following in the Preparing the Installation
> > section of the Setting up Samba as an Active Directory Domain Controller
> > document.
> >
> > "The host name and FQDN must not resolve to the 127.0.0.1 IP address or
> > any other IP address than the one used on the LAN interface of the DC."
> >
> > Link - Setting up Samba as an Active Directory Domain Controller -
> > Preparing the Installation
> >
> >   -
>
> https://wiki.samba.org/index.php/Setting_up_Samba_as_an_Active_Directory_Dom
> ain_Controller#Preparing_the_Installation
>
>
> AND
>
> [quote]
> I'm reading Kerberos - The Definitive Guide[1] and it makes the
>
> following comment:
> > And to make matters worse, some Unix systems map their own hostname
> > to 127.0.0.1 (the loopback IP address).
>
> [/quote]
>
> Caveat - not an expert, just my meager understanding:
>
> 1) The name 'localhost' is historically for developers who want to access
> their own machine _without_ using DNS.
>
> 2) By general practice sometime in the deep, dark times 127.0.0.1 was
> accepted for this purpose. There's nothing special about the address.
>
> 3) I read the original quoted comment in the Kerberos Guide as a warning -
> 'to make matters worse, __SOME__"
>
> 4) In my /etc/hosts I do _NOT_ map my machine's name to the same address as
> localhost, avoiding the Kerberos warning:
>
> mark@science:~$ cat /etc/hosts
> 127.0.0.1       localhost
> 127.0.1.1       science
>
> # The following lines are desirable for IPv6 capable hosts
>
> ::1     ip6-localhost ip6-loopback
>
> fe00::0 ip6-localnet
> ff00::0 ip6-mcastprefix
> ff02::1 ip6-allnodes
> ff02::2 ip6-allrouters
>
> mark@science:~$ ping localhost
> PING localhost (127.0.0.1) 56(84) bytes of data.
> 64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.032 ms
>
> mark@science:~$ ping science
> PING science (127.0.1.1) 56(84) bytes of data.
> 64 bytes from science (127.0.1.1): icmp_seq=1 ttl=64 time=0.032 ms
>
> mark@science:~$ hostname
> science
> mark@science:~$ hostname -I
> 192.168.86.42
> mark@science:~$ hostname -A
> science.lan
> mark@science:~$ hostname -f
> science
> mark@science:~$ hostname -i
> 127.0.1.1
> mark@science:~$

I think this is relevant to DNS resolution of/with domain controllers and may 
depend on the AD/DC topology.  The idea is to use the LAN address of the box 
as the first address in /etc/hosts and use 127.0.0.1 as the second address in 
the file.  If more AD/DNS servers exist in the network, then 127.0.0.1 could 
be even further down the list.

https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/ff807362(v=ws.10)?redirectedfrom=MSDN

I haven't over-thought this and there may be more to it, but on a pure linux 
environment I expect this would not be a requirement, hence the handbook 
approach.