NTP Server on Cisco Router (part II)

Earlier post I wrote about NTP server with 1 router.

This time let configure with more than 1 router within Intranet network.
Internet <--->HQ<---->Client1
<---->Client2
1st, configure on HQ router.
configure for access-list that only have to access ntp service
(config)#access-list 77 remark AllowNTPquery
(config)#access-list 77 permit 10.101.255.0 0.0.0.255 <--10.101.255.0/24 network only (config)#access-list 77 permit 203.127.86.243

(config)#ntp access-group peer 77 <--neighbor router must match by access-list 77 (config)#ntp access-group serve-only 77 <--only access-list 77 can access
(config)#ntp server 203.127.86.243
(config)#ntp source FastEthernet0/1 <--Wan Interface or that port synchronize ntp service On Client1 Router configuration,
(config)#ntp access-group peer 77
(config)#ntp server 10.101.255.1 source FastEthernet0/0 <--10.101.255.1 is HQ's Router ip address, fa0/0 must be able to access to HQ's Router ip

Note: you can find out free public NTP server from below link
http://tf.nist.gov/tf-cgi/servers.cgi#

On Client2 Router, I will configure with sntp
(config)#sntp server 10.101.255.1 version 3

with #debug ntp sync command, you can see ntp sync to which server
for disable debug, #u all (or) #no debug ntp sync

You can verify ntp synchronize by these commands
#show ntp status
Clock is synchronized, stratum 3, reference is .....
#show ntp associations
address ref clock st when poll reach delay offset disp
~203.127.86.243 192.36.143.150 2 10929 64 0 13.6 -0.14 16000

Verify for sntp command is
#show sntp
10.101.255.1 2 3 00:00:37 Synced