SNTP client doesn't receive answer packet from server

Unanswered Question
Apr 3rd, 2009



sntp server

.Apr 3 21:18:09: Sending SNTP packet to

.Apr 3 21:18:09: xmt CD80DF71.34FCA539 (21:18:09.206 CEST Fri Apr 3 2009)


Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:


Success rate is 100 percent (5/5), round-trip min/avg/max = 36/42/56 ms

On an other c1751-V router which is directly connected to SNTP server's LAN:

K16_dgr#sh sntp

SNTP server Stratum Version Last Receive 6 1 00:00:55 Synced

The problematic c805 router is directly connected to K16_dgr's WAN port. (its IP address of LAN if. is:

Any solutions?


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Overall Rating: 3 (4 ratings)
Leo Laohoo Fri, 04/03/2009 - 18:09

Errr ... I don't get your problem. When you do a "sh sntp" you get the result of "Synced". If you noticed in the Last Receive section, it says that it was last "Synced" 00:00:55 seconds. It looks like your SNTP settings is working.

What I would like to know is how is 1700's time clock set? By NTP, SNTP or did you hardcode the time yourself?

aruzsinszky Sat, 04/04/2009 - 08:27


Sorry if my description was wrong.

C805 is the problematic router, not the C1751-V (K16_dgr).

Both of them using the same source clock from which is a C1721 router.

I can ping from C805 and I checked the SNTP request packed reached the source and the answer was sent back.

K16_dgr using SNTP, too.

C805 is behind C1751-V on the WAN.


Leo Laohoo Sat, 04/04/2009 - 16:59

1700 series routers are capable of using NTP. Some 800 series routers, unfortunately, can only use SNTP.

Configure the 1700 to synchronize themselves using NTP while synchronize the 803 to the 1700 using SNTP.

aruzsinszky Sun, 04/05/2009 - 01:39

My C1721 is in NTP mode. C805 works only with SNTP.

The SNTP packet reaches C1721. It answer for the SNTP request. C805 can't see (or receive, or anything else) that packet.

Ping is working between C1721 and C805.

C1721 and C805 aren't in the same subnet.

Can the C1721 in SNTP mode be a server for other other SNTP client? I think, no.


Leo Laohoo Sun, 04/05/2009 - 03:11

Can the C1721 in SNTP mode be a server for other other SNTP client?

Yup. I've done it in my network several times. The 2960 switch was synchronized using NTP while the Wirelss AP's synchronize to the switch using SNTP.

Hope this answers your question.

aruzsinszky Sun, 04/05/2009 - 03:23

No, my C1721 is in NTP. Just in NTP.

Other C1751-V is syncronised to it by SNTP.

Other routers and switches (C2940) are syncronised, too. (by NTP).

C805 isn't syncronised.

Could you show me your SNTP _server_ config?


Leo Laohoo Sun, 04/05/2009 - 14:30

Try synchronizing your 805 to the C1721 or the 2940 switch via SNTP (SNTP server ).

aruzsinszky Mon, 04/06/2009 - 00:31

As I mentioned here in some letters connecting to C1721 doesn't work.

Many other devices (Cisco routers, switches) are able to syncronise to it but that C805 not.


aruzsinszky Mon, 04/06/2009 - 03:03

Yes, I found there is NTP command in my IOS so I use it.

SNTP doesn't work and I don't know why.

Best regards,

Leo Laohoo Mon, 04/06/2009 - 15:42

Thanks for the rating.

I agree. The early versions of the 800 series router, the 80X have NTP option. But from the 810 to the 850 series uses SNTP. Weird!


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