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

[Justin Shore]

Jared Mauch wrote:
> On Nov 23, 2009, at 3:19 PM, Justin Shore wrote:
> 
>> I noticed other changes between 24T1 and 24T2 that bit me this weekend when I upgraded 2 routers that are my NTP servers.  First off all the NTP config that was moved way up in the config in an earlier release suddenly got moved back to where it was.  Not a big deal but it makes RANCID unhappy.  Second, and this is a bad problem, it removed my "ntp source <int>" command from the config.  I didn't notice until today that my NTP servers weren't syncing up right.  Reviewing the RANCID diff pointed out the problem.
>>
>> This happened on both of the routers that I upgraded from 24T1 to 24T2.  I haven't rebooted either router to see if the problem will happen after every 24T2 reboot or if it's tied to the moving around of the config between 24T1 and 24T2.  My guess would be the latter, at least I hope that's the case.  I've contacted TAC to report this bug.
> 
> Cisco does not have a coherent config order that will be output.
> 
> This is something people need to continue to repeat to Cisco that this stuff actually matters.  The folks that do testing of software rarely perform anything from a non-console connection.  This has implications on the ability for them to watch and control this.  People don't understand that moving lines of code have real-world implication on diff based utilities used to manage routers.

Yeah, I've noticed config lines move after code updates before too and 
it's really annoying.  Usually it's something small like adding or 
removing exclamation points.  Occasionally things get re-ordered.  This 
was the first wholesale move of all related lines I've seen in a while.

I talked with TAC about the problem.  It took a while to get the 
engineer to understand the problem but I think we got there.  If not I 
will requeue.  He pointed me to a known bug:  CSCsx21595.  He kept 
saying that this problem was fixed in 24T2 and only affected 3800s.  To 
the best of my knowledge the problem (removal of existing 'ntp source' 
config line) was created by 24T2.  I never encountered it prior to that 
on any of my routers, including those running 24T and 24T1.  I also 
experienced the problem on a 7206 (G1).  Clearly this isn't isolated to 
just 3800s.  I haven't had a chance to test it on anything else but I 
fully expect to see the same results on all routers I test it on.  I 
have no reason to expect otherwise.

Anyway, the problem is known.  I'll give it a few days and push on it if 
nothing happens.  To recreate the problem I imagine one would just need 
to have a basic NTP config with the ntp source interface defined as a 
virtual interface (the bug said it depended on that) so use an SVI or 
loopback.  Then upgrade to 24T2.  I suspect one would need to upgrade 
from 24T first and then upgrade to 24T2.  I suspect the problem is in 
the parser when IOS first loads the config from the older release.  I'd 
bet money that the startup-config was intact when I booted and that only 
the running-config was altered after that first boot.

Justin