[CentOS] CentOS 6 as DNS-Server

Hello,

it has been a while since I had setup a DNS-Server with CentOS 6;
these days I added a few zones needed for DDNS; this works
but in /etc/ I found quite a strange file, I'm not sure if it was in use
at the beginning I used this system as a DNS-Server, and after several
'yum update'
not any more;

/etc/named.root.key with this content

managed-keys {
# DNSKEY for the root zone.
# Updates are published on root-dnssec-announce at icann.org
. initial-key 257 3 8
"AwEAAagAIKlVZrpC6Ia7gEzahOR+9W29euxhJhVVLOyQbSEW0O8gcCjF
FVQUTf6v58fLjwBd0YI0EzrAcQqBGCzh/RStIoO8g0NfnfL2MTJRkxoX
bfDaUeVPQuYEhg37NZWAJQ9VnMVDxP/VHL496M/QZxkjf5/Efucp2gaD
X6RS6CXpoY68LsvPVjR0ZSwzz1apAzvN9dlzEheX7ICJBBtuA6G3LQpz
W5hOA2hzCTMjJPJ8LbqF6dsV6DoBQzgul0sGIcGOYl7OyQdXfZ57relS
Qageu+ipAdTTJ25AsRTAoub8ONGcLmqrAmRLKBP1dfwhYB4N7knNnulq
QxA+Uk1ihz0=";
};

and /etc/named.iscdlv.key with a content
identical to this: http://ftp.isc.org/isc/bind9/keys/9.8/bind.keys.v9_8

in no file neither in /etc/named.conf nor in any other file that is
included by the main config I can find a reference to /etc/named.root.key

is this file really needed or did it become obsolete?
(as seen on the URL above, /etc/named.root.key is part of
/etc/named.iscdlv.key)

Thanks,
Walter