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Need to do some reading on local domains on the internal network

Posted by jpluimers on 2021/04/09

A long time I wondered why I saw ESXi systems on my local network have two entries in their /etc/hosts file:

[root@ESXi-X10SRH-CF:~] cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1   localhost.localdomain localhost
::1     localhost.localdomain localhost
192.168.71.91   ESXi-X10SRH-CF ESXi-X10SRH-CF

Then I bumped into someone who had a different setup:

[root@ESXi-X10SRH-CF:~] cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1   localhost.localdomain localhost
::1     localhost.localdomain localhost
192.168.0.23    esxi.dynamic.ziggo.nl esxi

So now I knew that the first entry can have a domain resolving it (it still makes be wonder why ziggo is using a top-level domain to resolve local stuff; but searching for  dynamic.ziggo.nl did not get me further on that).

So I installed a quick ESXi machine on that local network, and got the same.

When back home the machine still thought it was esxi.dynamic.ziggo.nl, though clearly I was outside a Ziggo network

I wanted to get rid of it, but that was hard.

Since I forgot to take screenshots beforehand, I can only provide the ones without a search domain bellow.

Reminder to self: visit someone within the Ziggo network, then retry.

Normally you can edit things like these in the default TCP/IP stack. There are two places to change this:

Neither of these allowed me to change it to a situation like this, but luckily the console did.

In the below files, I had to remove the bold parts, then restart the management network (I did keep a text dump, lucky me):

[root@esxi:/etc] grep -inr ziggo .
./vmware/esx.conf:116:/adv/Misc/HostName = "esxi.dynamic.ziggo.nl"
./resolv.conf:2:search dynamic.ziggo.nl 
./hosts:5:192.168.71.194    esxi.dynamic.ziggo.nl esxi
[root@esxi:/etc] cat /etc/resolv.conf 
nameserver 192.168.71.3
search dynamic.ziggo.nl 
[root@esxi:/etc] cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1   localhost.localdomain localhost
::1     localhost.localdomain localhost
192.168.71.194  esxi.dynamic.ziggo.nl esxi

Future steps

  1. Read more on local domains, search domains and related topics
  2. Configure a local domain on my local network, so DHCP hands it out, and DHCP handed out host names are put in the local DNS
  3. Test if all services on all machines still work properly

Reading list

–jeroen

Screenshots without a search domain

Web interface

DCUI

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