How does configuring both `search` and `domain` in a `/etc/resolv.conf` effect DNS short name query sequence?

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux (RHEL)
    • 8
    • 7

Issue

  • What will the DNS search sequence be if both search and domain directives are configured in a /etc/resolv.conf?

Resolution

  • According to the implementation of Glibc, if domain and search directives are both used, only the last instance will be used for DNS queries.

Diagnostic Steps

  • The instance, /etc/resolv.conf shows that the domain directive is configured to example.com and followed by the search directive which is configured to redhat.com:

    [root@localhost etc]# cat resolv.conf
nameserver 8.8.8.8
domain example.com
search redhat.com

[root@localhost resolv]# nslookup www
Server:     8.8.8.8
Address:    8.8.8.8#53

Non-authoritative answer:
www.redhat.com  canonical name = ds-www.redhat.com.edgekey.net.                 <----- Only the last instance, "search" is used for the DNS query.
ds-www.redhat.com.edgekey.net   canonical name = ds-www.redhat.com.edgekey.net.globalredir.akadns.net.
ds-www.redhat.com.edgekey.net.globalredir.akadns.net    canonical name = e3396.dscx.akamaiedge.net.
Name:   www.example.com 
Address: 184.xx.xx.xx
Name:   www.example.com 
Address: 00:00:00:00:00:aa
Name:   www.example.com 
Address: 00:00:00:00:00:aa

  • In another example, the search directive is configured and followed by the domain directive:

    [root@localhost etc]# cat resolv.conf
nameserver 8.8.8.8
search redhat.com
domain example.com

[root@localhost resolv]# nslookup www
Server:     8.8.8.8
Address:    8.8.8.8#53

Non-authoritative answer:
Name:   www.example.com                          <------- Only the last instance, "domain" is used for the DNS query.
Address: xxx.xxx.xxx.xxx
Name:   www.example.com
Address: xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx

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