NTPとNAT

ちょっとテストしてわかったこと。
NTPサーバのIPアドレスに対し　 IP reachable だからといって
同期するものではないらしい。


NATを以下の設定
Router#sh ip nat translations
Pro Inside global Inside local Outside local Outside global
---　---　　　　　　　　---　　　　　　　　1.1.1.1　　　　　　172.16.1.1
Router#

続いて、NTPサーバを 172.16.1.1 と指定。



Router#
Router#ping 172.16.1.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/9/12 ms
Router#

だけど、


Router#sh ntp status
Clock is unsynchronized, stratum 16, no reference clock
nominal freq is 250.0000 Hz, actual freq is 249.9999 Hz, precision is 2**19
reference time is CCA0F71E.4874877C (23:11:26.283 UTC Wed Oct 15 2008)
clock offset is 0.9669 msec, root delay is 10.83 msec
root dispersion is 2.35 msec, peer dispersion is 1.36 msec
Router#

と同期しない。


debug すると。

Router#
.Oct 15 23:18:18.137: NTP: xmit packet to 172.16.1.1:
.Oct 15 23:18:18.137: leap 3, mode 3, version 3, stratum 0, ppoll 64
.Oct 15 23:18:18.141: rtdel 02C6 (10.834), rtdsp 009B (2.365), refid 01010101 (1.1.1.1)
.Oct 15 23:18:18.141: ref CCA0F71E.4874877C (23:11:26.283 UTC Wed Oct 15 2008)
.Oct 15 23:18:18.145: org 00000000.00000000 (00:00:00.000 UTC Mon Jan 1 1900)
.Oct 15 23:18:18.149: rec 00000000.00000000 (00:00:00.000 UTC Mon Jan 1 1900)
.Oct 15 23:18:18.153: xmt CCA0F8BA.22552FB4 (23:18:18.134 UTC Wed Oct 15 2008)
.Oct 15 23:18:18.169: NAT*: s=172.16.1.1->1.1.1.1, d=192.168.1.1 [0]
.Oct 15 23:18:18.177: NTP: rcv packet from 1.1.1.1 to 192.168.1.1 on Ethernet0:
Router#


そこで、NTPサーバのアドレスを　 Outside local に変更してみると。

Router#sh ntp associations

address ref clock st when poll reach delay offset disp
*~1.1.1.1 .LOCL. 1 18 64 377 18.7 3.08 0.4
* master (synced), # master (unsynced), + selected, - candidate, ~ configured

と同期


debug　の結果は

.Oct 15 23:19:54.133: NAT: s=192.168.1.1, d=1.1.1.1->172.16.1.1 [0]
.Oct 15 23:19:54.137: NTP: xmit packet to 1.1.1.1:
.Oct 15 23:19:54.141: leap 3, mode 3, version 3, stratum 0, ppoll 64
.Oct 15 23:19:54.141: rtdel 02C6 (10.834), rtdsp 009B (2.365), refid 01010101 (1.1.1.1)
.Oct 15 23:19:54.145: ref CCA0F71E.4874877C (23:11:26.283 UTC Wed Oct 15 2008)
.Oct 15 23:19:54.149: org 00000000.00000000 (00:00:00.000 UTC Mon Jan 1 1900)
.Oct 15 23:19:54.153: rec 00000000.00000000 (00:00:00.000 UTC Mon Jan 1 1900)
.Oct 15 23:19:54.157: xmt CCA0F91A.2258D7F9 (23:19:54.134 UTC Wed Oct 15 2008)
.Oct 15 23:19:54.173: NAT*: s=172.16.1.1->1.1.1.1, d=192.168.1.1 [0]
.Oct 15 23:19:54.181: NTP: rcv packet from 1.1.1.1 to 192.168.1.1 on Ethernet0:
.Oct 15 23:19:54.181: leap 0, mode 4, version 3, stratum 1, ppoll 64
.Oct 15 23:19:54.185: rtdel 0000 (0.000), rtdsp 0002 (0.031), refid 4C4F434C (76.79.67.76)
.Oct 15 23:19:54.189: ref CCA0F8E2.FE16DA50 (23:18:58.992 UTC Wed Oct 15 2008
R)
.Oct 15 23:19:54.193: org CCA0F91A.2258D7F9 (23:19:54.134 UTC Wed Oct 15 2008)
.Oct 15 23:19:54.197: rec CCA0F91A.25BC8E93 (23:19:54.147 UTC Wed Oct 15 2008)
.Oct 15 23:19:54.201: xmt CCA0F91A.2CE694EF (23:19:54.175 UTC Wed Oct 15 2008)
.Oct 15 23:19:54.205: inp CCA0F91A.2E538C16 (23:19:54.180 UTC Wed Oct 15 2008)
.Oct 15 23:19:54.209: NTP: 1.1.1.1 reachable
Oct 15 23:19:54.209: NTP: sync change
Oct 15 23:19:54.213: NTP: peer stratum change


NTP: 1.1.1.1 reachable　が重要みたい。