You all are on the right track but I see some confusion about the delay in the ntp sync process. It is important to understand how ntp sync occurs, and in the process answering several of the questions that get asked here in this thread and in the past.
Recommended reading: http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/vcallcon/ps556/prod_white_paper0900aecd8037fdb5.html This is an excerpt of a source on unix ntp, which is all very much the same as they all follow RFC from:http://www.akadia.com/services/ntp_synchronize.html "...the process starts when the NTP client sends a packet containing its timestamp to a server. When the server receives such a packet, it will in turn store its own timestamp and a transmit timestamp into the packet and send it back to the client. When the client receives the packet it will log its receipt time in order to estimate the travelling time of the packet. The packet exchange takes place until a NTP server is accepted as a synchronization source, which take about five minutes." Check out the exact calculation of ntp at:http://en.wikipedia.org/wiki/Network_Time_Protocol#Clock_synchronization_algorithm So in the cisco world, the IOS follows the RFC but there are some bugs to watch out for. I have hit all of these in the field and lab at some point and had them bookmarked so I pasted them below. The most important thing to note is your IOS version. To sum it up: -ntp master sets the router to its own clock, causing the ntp status to "sync right away" as others have noticed.By no means does that make a requirement met on a lab =) -Use the ntp source command -Be watchful of these bugs. -Even if you have configuration requirements met, your odds are you will need to reboot the router based off the bugs and IOS versions below. -NTP sync to a peer other than itself takes time. -generally don't use ntp master to avoid the bug and good practice as there are many more valid NTP sources out there. One other thing I see people trip up on is SNTP. This is the Windows implementation of time through w32time service. These are not operable between a router or other NTP(CUCM) device unless the service is disabled and a ntp server is installed on the box locally. I have seen others complain about syncing the router to the cucm but never achieving sync; yet after hours to find out that it was the CUCM that was not syncd because of SNTP/NTP between CUCM/Win2003. Now in NTPv4 there are SNTP definitions. NTP has been around for as long as I have been alive, the RFCs are well known and one of the slowest changing standards. Check them out, they are a good read. http://tools.ietf.org/html/rfc1305 http://tools.ietf.org/html/rfc5905 CSCsu36827 Symptoms: The CUE clock does not synch up with the CME using NTP. Conditions: This symptom is observed when the UC500 is configured as the NTP master. Workaround: Use an external NTP server other than the UC500. http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCsu36827&from=summary CSCtf88705 Symptom: NTP sync lost after failover and ip change on an interface. Workaround: Remove and reconfigure NTP http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCtf88705&from=summary CSCsw28386 Symptom: NTP sync fails after routing failover Conditions: The problem occurs with 12.4(22)T. The problem does not occur with 12.4(23). Workaround: reload the device or reconfigure ntp http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCsw28386&from=summary CSCsj68446 Symptoms: NTP may not sync, When a device is configured to receive NTP packets and its receiving NTP packets, but not processing it at all. The NTP packets seem to get ignored by the NTP process. Conditions: -When virtual interfaces are deleted and added again. - And in other conditions. - It is independent of platforms. Frequency: Rare Case Impact:It may affect timing synchronization. Workaround: Re-configure NTP, would solve the issue. Issuing "no ntp" command twice would solve the issue. Reloading the box, will re-start the NTP process and it works fine. http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCsj68446&from=summary CSCei77073 NTP client need to reset auto learnt source IP address Release-note: ------------- The Cisco IOS NTP uses the same source IP address to send packets even if it deosnot get reply via that interface. This is not applicable for source configured via *ntp source* command. http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCei77073&from=summary CSCsw30737 NTP does not synchronize if both ntp master and ntp server configured Symptom: NTPv4 does not synchronize with IOS 12.4(20)T and later releases. The router does not even synchronize with its own internal clock. Conditions: Need to have both ntp master and ntp server configured. If only NTP master or NTP server is configured, the router can synchronize fine with the defined time source. Workaround: If configuring only "ntp master" or "ntp server", the router will synchronize http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCsw30737&from=summary On Mon, Sep 19, 2011 at 9:53 AM, Ray <jonha...@yahoo.com> wrote: > yes you lower the stratum at HQ with the ntp master command, but the issue > is the UTC server has the higest stratum... so if you put any stratum on HQ > it will only syn to itself and not the UTC server.... higher stratum will > syn from lower stratum that is how it works.. I am going to put only ntp > server and ntp source on hq and set the ntp on cucm to be hq loopback and > let it set for hours and see it can syn again... if it doesnt syn i will > put the ntp master and reboot and see if it syns.. > ________________________________ > From: Ashraf Ayyash <ash.ayy...@gmail.com> > To: Justin Barksdale <jus...@barksdale.net> > Cc: Ray <jonha...@yahoo.com>; "ccie_voice@onlinestudylist.com" > <ccie_voice@onlinestudylist.com> > Sent: Monday, September 19, 2011 8:51 AM > Subject: Re: [OSL | CCIE_Voice] ntp > > Hello All , > > i have review the NTP principle again with my Colleagues and with Amit > who did lab for this ( Thanks ALOT) and we have done some show > commands on the CCM and the IOS in regard of this issue > > what we found is that the the lowest stratum is the Best and stratum > -0 is the lowest value we have in Cisco world, > what Justin and the other stated is correct , we will not need Master > command to sync the other internal network components to the HQ router > , its enough to sync HQ with the UTC based server and then the other > routers should take the time correctly from the HQ on UTC based as > well > > the CCM pub is stratum 11 by default and the SUB is 12 , do utils ntp > status before you sync them , so based on the above , to sync the CCM > with the HQ ntp please make sure that you have Stratum lower than 11 > at your HQ and you should be good to go , > > Justain , Amit , everyone , thank you for sharing / discussing this > issue , this is very helpful and add new info for me and i hope the > same happened for another people > > Best Regards > > Ash > > On Sun, Sep 18, 2011 at 11:11 PM, Justin Barksdale <jus...@barksdale.net> > wrote: >> If this is the case then the address you are pointing to at the pstn is >> incorrect. If you add the ntp server to the router and do show ntp status >> the router MUST be syncing with an external source or UCM will not sync. >> Furthermore a reboot is not required on UCM or ther router. Simply add >> the >> address to UCM and do utils ntp restart from cli. The key is that the ntp >> source the router is syncing with must be valid. >> >> Sent from my iPhone 4. >> On Sep 19, 2011, at 1:12 AM, Ray <jonha...@yahoo.com> wrote: >> >> Ntp is not slow when i put the ntp master command on HQ router and the >> cucm >> syn right the way. i took off the ntp master from the hq and only have ntp >> server and ntp source lo0. and reboot the cucm and the hq. and let it set >> for 4hrs to 5hrs and the cucm would not syn, but the moment i put the ntp >> master it syns within 2 mins... you can try it in you lab and let me >> know.. >> make sure you reboot the cucm and the hq router... >> ________________________________ >> From: Justin Barksdale <jus...@barksdale.net> >> To: "ccie_voice@onlinestudylist.com" <ccie_voice@onlinestudylist.com> >> Sent: Sunday, September 18, 2011 9:14 PM >> Subject: Re: [OSL | CCIE_Voice] ntp >> >> NTP is by nature slow. An earlier post pointed out the correct method. >> If >> the question wants you to sync hq with the pstn and then ccm with hq then >> the ntp master command will break this requirement. All that is required >> on >> the HQ router is ntp server x.x.x.x >> >> This is also mentioned in Vic's class class as well as Cisco >> documentation. >> The important key here is that the ntp master command can cause you to >> override a valid external time source and thus can be very dangerous. As >> long as the ntp server command points to a valid and reachable ntp source >> then the hq router will sync and you WILL be able to sync ucm without the >> ntp master command. >> >> Justin Barksdale >> CCIE# 29866 >> Voice >> >> Sent from my iPhone 4. Please excuse any typos. >> >> On Sep 18, 2011, at 7:39 PM, ccie_voice-requ...@onlinestudylist.com wrote: >> >>> Re: [OSL | CCIE_Voice] ntp >> _______________________________________________ >> For more information regarding industry leading CCIE Lab training, please >> visit www.ipexpert.com >> >> Are you a CCNP or CCIE and looking for a job? Check out >> www.PlatinumPlacement.com >> >> >> >> _______________________________________________ >> For more information regarding industry leading CCIE Lab training, please >> visit www.ipexpert.com >> >> Are you a CCNP or CCIE and looking for a job? Check out >> www.PlatinumPlacement.com >> > > > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
