CHRONY
ISP
nano /etc/chrony.conf
ntp.msk-ix.ru
systemctl restart chronyd
HQ-RTR и BR-RTR
hq-rtr(config)#ntp server 172.16.1.1
hq-rtr(config)#write memory
br-rtr(config)#ntp server 172.16.2.1
br-rtr(config)#write memory
HQ-CLI и HQ-SRV
nano /etc/chrony.conf
systemctl restart chronyd
BR-SRV
nano /etc/chrony.conf
server 172.16.2.1 iburst