[c-nsp] New feature, can't find it documented - NTP using DNS

[Church, Charles]

Hey all,

	Ran across this by accident on a 871 running 12.4(24)T2:

DE-Atlanta(config)#ntp server ?
  A.B.C.D     IP address of peer
  WORD        Hostname of peer
  X:X:X:X::X  IPv6 address of peer
  ip          Use IP for DNS resolution
  ipv6        Use IPv6 for DNS resolution
  vrf         VPN Routing/Forwarding Information

DE-Atlanta(config)#ntp server ip ?
  WORD  Hostname of peer

DE-Atlanta(config)#ntp server ip pool.ntp.org ?
  burst    Send a burst when peer is reachable
  iburst   Send a burst when peer is unreachable
  key      Configure peer authentication key
  maxpoll  Maximum poll interval
  minpoll  Minimum poll interval
  prefer   Prefer this peer when possible
  source   Interface for source address
  version  Configure NTP version
  <cr>

DE-Atlanta(config)#ntp server ip pool.ntp.org
Translating "pool.ntp.org"...domain server (12.127.16.67) [OK]

DE-Atlanta#sh run | i ntp
ntp server ip pool.ntp.org
ntp server 64.73.32.134
ntp server 207.46.197.32
DE-Atlanta#sh ntp ass

  address         ref clock       st   when   poll reach  delay  offset   disp
 ~38.229.71.1     192.168.0.16     2      3     64     7  0.000 658.174 1938.4
 ~64.73.32.134    4.213.182.128    2     40     64     3  0.000 665.796 3937.7
 ~207.46.197.32   169.229.70.64    3     44     64     3  0.000 655.923 3949.7
 * sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured
DE-Atlanta#
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Been wanting this for years.  Any idea what this feature is called?  Didn't see anything in the release notes or feature navigator about it.  Curious if it honors DNS TTLs, etc.  I do see that it's negotiated V4 on these peers, but I don't think it's a function of NTP V4.

Thanks,

Chuck