<div><div dir="auto">Thanks for the reply Petr.</div><div dir="auto">Let me explain more about the motivation: I am a developer and our testers test the code on various environments, including VMs on cloud and k8s worker nodes from cloud providers. These machines and IPs are not provisioned/allocated by dnsmasq. For cost reason, these environments only lives for a short period of time, like one week or so, and testers provision these IPs directly without awareness of network administrators, that’s also why we don’t configure hostname for these machines in DNS system. Also I can not know in advance the list of possible IPs.</div><div dir="auto"><br></div><div dir="auto">Whenever tester find some issue or need help, they give me the IP of the environments and I need to ssh to that environment. Because I will probably login to that same machine several times since the testers are testing my code on that machine recently, I want to setup passwordless login. So I normally ssh-copy-id -i <~/.ssh/<a href="http://id_rsa.work" target="_blank">id_rsa.work</a>> <IP>first, then ssh to that machine. In order to instruct ssh to use my ssh key when connecting to that IP, I have below lines in my .ssh/config:</div></div><div><div dir="auto"><span style="word-spacing:1px;border-color:rgb(49,49,49);color:rgb(49,49,49)"><br></span></div><div dir="auto"><span style="word-spacing:1px;border-color:rgb(49,49,49);color:rgb(49,49,49)">Host *.mylab</span></div><div dir="auto"><span style="word-spacing:1px;border-color:rgb(49,49,49);color:rgb(49,49,49)"> User root</span></div><div dir="auto"><span style="word-spacing:1px;border-color:rgb(49,49,49);color:rgb(49,49,49)"> IdentityFile ~/.ssh/</span><a href="http://id_rsa.work/" style="font-size:1rem;word-spacing:1px;border-color:rgb(66,133,244)" target="_blank">id_rsa.wor</a>k</div><div dir="auto"><br></div></div><div><div dir="auto">And lines like below in /etc/hosts:</div><div dir="auto"><span style="word-spacing:1px;border-color:rgb(49,49,49);color:rgb(49,49,49)">address=/<a href="http://123.123.123.123" style="border-color:rgb(66,133,244)" target="_blank">123.123.123.123</a>.</span><span style="word-spacing:1px;border-color:rgb(49,49,49);color:rgb(49,49,49)">mylab/</span><a href="http://123.123.123.123/" style="font-size:1rem;word-spacing:1px;border-color:rgb(66,133,244)" target="_blank">123.123.123.123</a></div><div dir="auto"><span style="word-spacing:1px;border-color:rgb(49,49,49);color:rgb(49,49,49)">address=/<a href="http://123.123.123.123" style="border-color:rgb(66,133,244)" target="_blank">123.123.123.12</a>4.</span><span style="word-spacing:1px;border-color:rgb(49,49,49);color:rgb(49,49,49)">mylab/</span><a href="http://123.123.123.123/" style="font-size:1rem;word-spacing:1px;border-color:rgb(66,133,244)" target="_blank">123.123.123.12</a>4<br></div><div dir="auto"><br></div><div dir="auto">So that I can now “ssh 123.123.123.123.mylab” </div><div dir="auto"><br></div><div dir="auto">As you can see, the problem here is, whenever a new IP comes, I need to add a new entry in /etc/hosts. So what I want is any <IP>.mylab is resolved to <IP>.</div><div dir="auto"><br></div><div dir="auto">A key pair can be specified when creating VM on cloud, but I can not ask every tester add my ssh key pair when creating VM.</div><div dir="auto"><br></div><div dir="auto"><br></div><div><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Petr Menšík <<a href="mailto:pemensik@redhat.com" target="_blank">pemensik@redhat.com</a>>于2022年11月25日 周五19:52写道：<br></div></div></div></div><div><div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
<div>
<p>Did you know that dnsmasq registers all hosts by their name, if
they send their own hostname when requesting DHCP from dnsmasq?
Just use domain=mylab and have that host send hostname. It would
make using names possible without any additional configuration.<br>
</p>
<p>I do not get what is the advantage of having IP suffixed by some
domain. It looks like IP address, but it is even longer. Names of
machines should be easy to remember or use, I doubt that would be
the case here.</p>
<p>I think we have new feature conf-script, which can generate
dnsmasq configuration on the output. But I doubt we have a
possible code for what you describe. Could you please describe
more about intended usage? Why isn't using just hostname for each
host enough? Using dhcp-host seems enough for similar uses.<br>
</p>
<p>I think DLZ plugins for BIND9 are able to do similar things to
your request, but that would be very heavy-weight solution. I
think more motivation for your current design should be shared,
because I do not understand advantage of your solution.</p>
<p>Cheers,<br>
Petr<br>
</p></div><div>
<div>On 11/23/22 06:47, Feng Shao wrote:<br>
</div>
</div><div><blockquote type="cite"></blockquote></div><div><blockquote type="cite">
<span style="word-spacing:1px;color:rgb(49,49,49)">There are a
bunch of machines in our lab, and we normally don't have DNS
records configured for them, only accessing by IP. In order to
ssh to them with key auth, I have a config in my .ssh/config
like </span><br style="color:rgb(49,49,49);word-spacing:1px">
<br style="color:rgb(49,49,49);word-spacing:1px">
<span style="word-spacing:1px;color:rgb(49,49,49)">Host *.mylab</span><br style="color:rgb(49,49,49);word-spacing:1px">
<span style="word-spacing:1px;color:rgb(49,49,49)"> User root</span><br style="color:rgb(49,49,49);word-spacing:1px">
<span style="word-spacing:1px;color:rgb(49,49,49)"> IdentityFile
~/.ssh/</span><a href="http://id_rsa.work/" style="font-size:1rem;word-spacing:1px" target="_blank">id_rsa.work</a><br style="color:rgb(49,49,49);word-spacing:1px">
<br style="color:rgb(49,49,49);word-spacing:1px">
<span style="word-spacing:1px;color:rgb(49,49,49)">and I have some
"address=/<a href="http://123.123.123.123" target="_blank">123.123.123.123</a>.</span><span style="word-spacing:1px;color:rgb(49,49,49)">mylab/</span><a href="http://123.123.123.123/" style="font-size:1rem;word-spacing:1px" target="_blank">123.123.123.123</a><span style="word-spacing:1px;color:rgb(49,49,49)">" line in
dnsmasq.conf. The problem here is I need to add an entry
whenever a new IP comes.</span><br style="color:rgb(49,49,49);word-spacing:1px">
<br style="color:rgb(49,49,49);word-spacing:1px">
<span style="word-spacing:1px;color:rgb(49,49,49)">Can this
configuration be dynamically? For example,
"address=/*.mylab/somecmd %1", where "somecmd" is a external
command and %1 will be replaced by the name in A/AAAA request.
So that for any DNS request to *.mylab, dnsmasq invoke this
external command and pass the name as argument, the output of
external command, which will be interpreted as IPv4/IPv6 addr
then responsed to client?</span>
<br>
<fieldset></fieldset>
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<pre cols="72" style="font-family:monospace">--
Petr Menšík
Software Engineer, RHEL
Red Hat, <a href="https://www.redhat.com/" style="font-family:monospace" target="_blank">https://www.redhat.com/</a>
PGP: DFCF908DB7C87E8E529925BC4931CA5B6C9FC5CB</pre>
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