NTP 时钟无法同步排查方法：
1、 V5设备NTP同步的版本默认是V3版本，V7设备默认是V4版本，如果直接在V7设备上配置NTP，NTP上的时钟可能无法实现同步的，需要手动将版本更改为V3就可以同步时钟了
V5设备查看版本如下：
[H3C]dis ntp sessions ver
[H3C]dis ntp sessions verbose
clock source: 10.1.12.1
clock stratum: 2
clock status: configured, master, sane, valid
reference clock ID: 127.127.1.0
local mode: active, local poll: 6
peer mode: passive, peer poll: 6
offset: -455.5000 ms,delay: 15.00 ms, disper: 16.90 ms
root delay: 0.00 ms, root disper: 34.29 ms
reach: 255, sync dist: 0.381, sync state: 5
precision: 2^7, version: 3, peer interface: wildcard
reftime: 11:19:45.885 UTC Nov 24 2016(DBE14B51.E28F5C28)
orgtime: 11:20:24.027 UTC Nov 24 2016(DBE14B78.06E978D4)
rcvtime: 11:20:24.490 UTC Nov 24 2016(DBE14B78.7D70A3D7)
xmttime: 11:20:24.475 UTC Nov 24 2016(DBE14B78.79999999)
filter delay : 0.02 0.02 0.02 0.02 0.02 0.03 0.03 0.01
filter offset: -0.46 0.00 0.00 0.00 0.00 -0.46 -0.46 -0.46
filter disper: 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02
Total associations : 1
V7设备查看版本如下：
[H3C]dis ntp-service sessions verbose
Clock source: 10.1.12.1
Session ID: 15127
Clock stratum: 2
Clock status: configured, candidate, sane, valid
Reference clock ID: 127.127.1.0
instance: Not specified
Local mode: sym_active, local poll interval: 6
Peer mode: sym_passive, peer poll interval: 6
Offset: -4.465ms, roundtrip delay: 0.4425ms, dispersion: 0.1373ms
Root roundtrip delay: 0.0000ms, root dispersion: 11.825ms
Reachabilities:3, sync distance: 0.0144
Precision: 2^-15, version: 4, source interface: Not specified
Reftime: dbe0fad3.88ccf3f1 Thu, Nov 24 2016 5:36:19.534
Orgtime: dbe0fb0c.4ece8e83 Thu, Nov 24 2016 5:37:16.307
Rcvtime: dbe0fb0c.4d362302 Thu, Nov 24 2016 5:37:16.301
Xmttime: dbe0fb0c.4d362302 Thu, Nov 24 2016 5:37:16.301
Roundtrip delay samples: 1.068 0.930 0.656 1.129 0.442 0.000 0.000 0.000
Offset samples: -6.85 -7.61 -3.89 -3.16 -4.47 0.00 0.00 0.00
Filter order: 4 2 1 0 3 5 6 7
ntp-service unicast-peer 10.1.12.1 version 3
2、 V7需要将时钟协议更改为NTP方式
[H3C]clock protocol ntp
3、 如果还是无法同步，在NTP同步时指定源接口
[H3C]ntp unicast-server 100.1.12.1 source g0/1