NTP

  1. Network time protocol (NTP)
  2. Simplified NTP (SNTP)

Network time protocol (NTP)

  • server selection:
    1. best stratum
    2. configured > bcast/mcast
    3. server, whose message is received first
  • modes
    1. peer
      • full access
      • the only mode that can become synchronized
    2. serve
      • reply to NTP requests and Control queries, drop NTP updates
    3. serve-only
      • reply to NTP requests only
    4. query-only
      • reply to Control queries only
  • ACL search: peer → serve → serve-only → query-only
  • bcast/mcast mode has lower precision
  • client authenticates server, server does not authenticate client
  • synchronization with stratum 15 is impossible
  • orphan mode: if server is lost, assume session being up – preserves sync with peer
  • version 4:
    • IPv6 support
    • hierarchy auto-build using mcast
    • X.509 support
; enabled authentication, does not enforce it, NTP server config
(config)# ntp authentication

(config)# ntp authentication-key <N> md5 <TEXT>

; permit to use key N
(config)# ntp trusted-key <N>

; prefer does not have priority over stratum
(config)# ntp server <IP> key <N> [prefer] [version 3|4]

; for master NTP ACL must permit 127.127.7.1, if deny is hit, other modes are not searched
(config)# ntp access-group peer|serve|serve-only|query-only <ACL>

; update hardware clock using NTP
(config)# ntp update-calender

(config)# ntp orphan <STRATUM>

; becaome NTP server 
(config)# ntp master <STRATUM>
(config)# clock timezone <TIMEZONE> <OFFSET>
(config)# clock summer-time <NAME> date ...
(config)# clock summer-time <NAME> recurring ...

; HW clock – authoritative source
(config)# clock calendar-valid
; server
(config-if)# ntp broadcast|multicast ... 

; client
(config-if)# ntp broadcast|multicast client
; HW clock, not reset across reboot
# calendar set <TIME>
# show ntp association detail
# show ntp status
# debug ntp packet
# debug ntp validity

Simplified NTP (SNTP)

  • client only, cannot function as server
  • less precise result
  • ntp commands → sntp commands
  • incompatible with NTP on same device: uses same port