SDI exercises related DNS server

This section explains how to define two publicly visible DNS A records to your VMs. The objective is defining two A records sdi1 and sdi2 within your respective DNS domain.

With respect to upcoming virtual host exercises the MI department provides a public DNS integrated Bind based server nssdi.mi.hdm-stuttgart.de allowing for CLI updates. This works as follows:

  • Each working group being registered below 113475 Software defined Infrastructure has access to a respective zone file defining a subdomain of sdi.mi.hdm-stuttgart.de.

    • Assuming you belong to group 3 your corresponding subdomain is g3.sdi.mi.hdm-stuttgart.de.

    • You'll find a dnsupdate.sec file containing the secret for authorizing your individual zone's management: 

      hmac-sha256:mykey.g3:I5sDDS3L1BUHNGWU2n7LEmkWJfNq/giDuXb1u076VjQ=

      Note

      The per zone secrets are being created using tsig-keygen. The value appearing here does not reflect a production setting.

  • nsupdate allows for zone management as being explained below.

Adding an A record for e.g. your second sdi2 VM requires: 

HMAC=hmac-sha256:mykey.g3:I5sDDS3L1BUHNGWU2n7LEmkWJfNq/giDuXb1u076VjQ=

goik>nsupdate -y $HMAC
> server nssdi.mi.hdm-stuttgart.de
> update add sdi2.g3.sdi.mi.hdm-stuttgart.de 86400 A 172.16.1.1
> send
> quit
goik>dig +noall +answer @nssdi.mi.hdm-stuttgart.de sdi2.g3.sdi.mi.hdm-stuttgart.de
sdi2.g3.sdi.mi.hdm-stuttgart.de. 86400	IN A	172.16.1.1

This entry will be globally visible:

goik>dig +noall +answer  sdi2.g3.sdi.mi.hdm-stuttgart.de
sdi2.g3.sdi.mi.hdm-stuttgart.de. 7069 IN A	172.16.1.1

You should now be able to use your VMs DNS name rather than its raw IP: 

>ssh ...@sdi2.g3.sdi.mi.hdm-stuttgart.de

Deleting this DNS record works accordingly: 

goik>nsupdate -y $HMAC
> server nssdi.mi.hdm-stuttgart.de
> 
> update del sdi2.g3.sdi.mi.hdm-stuttgart.de A
> send
> quit
goik>
goik>dig +noall +answer @nssdi.mi.hdm-stuttgart.de sdi2.g3.sdi.mi.hdm-stuttgart.de

Due to caching it'll however take up to you SOA or record specific settings for this deletion to be reflected globally. The subsequent query result indicates another 7069 seconds to go before issuing the next query: 

goik>dig +noall +answer  sdi2.g3.sdi.mi.hdm-stuttgart.de
sdi2.g3.sdi.mi.hdm-stuttgart.de. 7069 IN A	172.16.1.1
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