From: roehling@debian.org 
  
 Hi, 
  
 * Marc Haber  [2025-10-13 22:22]: 
 >The biggest question that I still have is why we are writing an 
 >/etc/hosts with "127.0.1.1 apollo.example.com apollo". Without that, 
 >the FQDN of the system is incorrect. But why 127.0.1.1? Arch Linux does 
 >it the same way, but they don't explain why, either. 
 Even though most people associate 127.0.0.1 with the loopback interface, 
 the whole 127.0.0.0/8 block is actually reserved for that purpose, and 
 *any* address in that block loops back to your own host (just for fun, 
 try "ssh 127.234.56.78" if you have an SSH server running on your 
 computer). 
  
 127.0.1.1 is not special, it merely happens to be an address that 
 a) maps to your own host, and 
 b) has no other name assigned to it which would conflict in a reverse 
 lookup (127.0.0.1 is mapped to "localhost"). 
  
 The usual "trick" to get your own domain name is via hostname 
 canonicalization, i.e, you run gethostbyname("apollo"), which returns 
 127.0.1.1, and afterwards gethostbyaddr(127.0.1.1), which returns 
 "apollo.example.com". The 127.0.1.1 entry in /etc/hosts makes this work 
 and still lets the software on your computer behave exactly as if your 
 computer had a static IP with a proper DNS entry, regardless of your 
 actual network setup. 
  
 >And why do we handle systems that get installed with IP 
 >autoconfiguration in a different way than we do for systems with their 
 >IP statically set. Should we not generate the 127.0.1.1 line even in 
 >the latter case? Do we, maybe? 
 I don't see any reason not to. I for one configured /etc/hosts that way 
 on all servers I set up. Maybe someone else has additional insight. 
  
 If you ask me, the roaming client is the more problematic case, as you 
 need to have a well-defined FQDN to generate the /etc/hosts entry. I 
 suppose it can be a bit awkward if you want the domain name to be 
 configured dynamically and the DHCP client has to rewrite /etc/hosts 
 each time you connect to a network, which is probably why systemd is 
 exploring alternative resolution mechanisms. 
  
  
 Cheers 
 Timo 
  
 -- 
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 €€€€€€€€€€€€€€€€€€€€€   €€€ Timo R€€hlin 
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