Re: bin/55011 dhcpcd(8) sets "localhost" as hostname

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

The following reply was made to PR bin/55011; it has been noted by GNATS.

From: Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>
To: roy%marples.name@localhost
Cc: gnats-bugs%NetBSD.org@localhost, tsutsui%ceres.dti.ne.jp@localhost
Subject: Re: bin/55011 dhcpcd(8) sets "localhost" as hostname
Date: Tue, 21 Apr 2020 20:05:11 +0900

 (sorry for a late response)
 > The default behaviour since dhcpcd-6.10 has been to install the 
 > 29-lookup-hostname as an example script rather than include it as a default script.
 > 
 > Without the default dhcpcd.conf, the hostname option will not be requested.
 > 
 > So this is expected.
 
 Ok, I see.
 
 > > - The default name of "localhost" is annoying for me because
 > >    it's also used by sysinst as default settings in /etc/hosts.
 > >    Blank is still better for me.
 > 
 > I've attached a patch below to address this.
 > Let me know if it works for you!
 
 I have not tested yet (sorry) but if it's changed to leave
 hostname empty, it's enough for me.
 
 > > Is there any intentional changes (lookup removal?) from 6.1.5 one?
 > 
 > The 29-lookup-hostname hook was removed from the default installation due to a 
 > lot of user complaints.
 > It's also IPv4 specific, although that could be improved.
 > I have no intention of restoring it as a default hook.
 > 
 > If you want a DHCP client to set the hostname, use the default dhcpcd.conf and 
 > ensure the hostname is set in the DHCP message.
 > 
 > OR, set this in /etc/dhcpcd.enter-hook
 > 
 > . /usr/share/examples/dhcpcd/hooks/29-lookup-hostname
 
 Now I've checked dhcpd.conf(5) manual and noticed "use-host-decl-names"
 entry:
 ---
            The use-host-decl-names statement
 
              use-host-decl-names flag;
 
              If the use-host-decl-names parameter is true in a given scope,
              then for every host declaration within that scope, the name
              provided for the host declaration will be supplied to the client
              as its hostname.  So, for example,
 
                  group {
                    use-host-decl-names on;
 
                    host joe {
                      hardware ethernet 08:00:2b:4c:29:32;
                      fixed-address joe.example.com;
                    }
                  }
 
              is equivalent to
 
                    host joe {
                      hardware ethernet 08:00:2b:4c:29:32;
                      fixed-address joe.example.com;
                      option host-name "joe";
                    }
 ---
 
 Then I've added "use-host-decl-names on;" to server's /etc/dhcpd.conf
 
 ---
 # Pass hostname to option host-name per each "host" declaration.
 use-host-decl-names on;
 
  [..]
 
 host roppa {
   hardware ethernet 00:c0:f6:xx:xx:xx;
   fixed-address roppa;
   server-name "mirage";
   option root-path "/r/export/NetBSD/x68k/root";
 }
 
 ---
 
 and now at least NetBSD/x68k 9.0 dhcpcd in sysinst can get
 an FQDN hostname as provided from the server.  Thanks.
 
 
 However, there are still two minor problems:
 
 (1) FQDN hostname
 
 As mentioned in hooks/30-hostname (or hooks/30-hostname.in in -current)
 it looks dhcpcd(8) sets FQDN hostname by default.
 (maybe using "domain-name" also provided by DHCP server?)
 
 ---
 # A value of server means just what the server says, don't manipulate it.
 # This could lead to an inconsistent hostname on a DHCPv4 and DHCPv6 network
 # where the DHCPv4 hostname is short and the DHCPv6 has an FQDN.
 # DHCPv6 has no hostname option.
 # RFC4702 section 3.1 says FQDN should be prefered over hostname.
 #
 # As such, the default is hostname_fqdn=true so that a consistent hostname
 # is always assigned.
 : ${hostname_fqdn:=true}
 ---
 
 However, it looks sysinst(8) in NetBSD 9.0 doesn't like FQDN hostname,
 so that it explicitly asks hostname again even after dhcpcd
 successfully gets an IP address and an FQDN hostname.
 
 Should sysinst(8) be fixed to handle FQDN name properly, or
 should we prepare customized "30-hostname" with "hostname_fqdn=false"
 for all installation media and specify it in
 src/distrib/common/list.dhcpcd?
 
 (2) description of dhcpd.conf(5) man page
 
 dhcpd.conf(5) from NetBSD 9.0 says the following in the
 "use-host-decl-names" section:
 ---
     It should be noted here that most DHCP clients completely ignore
     the host-name option sent by the DHCP server, and there is no way
     to configure them not to do this.  So you generally have a choice
     of either not having any hostname to client IP address mapping
     that the client will recognize, or doing DNS updates.  It is
     beyond the scope of this document to describe how to make this
     determination.
 ---
 
 I guess that's the reason why the dhclient(8) used a looked up hostname.
 
 Maybe we should patch (or send a request to change) this dhcpd.conf(5)
 description to reflect modern dhcpcd(8) behavior?
 
 Thanks,
 
 ---
 Izumi Tsutsui