What do I want?
A network architecture on time!!
Thanks to whom?
At the NTP protocol!!
Who will be my reference?
A stable and reliable time repository!!
There are two types of time repositories:
GMT (Greenwich Mean Time) or UT (Universal Time):
– Reference: Rotation of the Earth
– Measurement: Passages of celestial objects on a reference
– Precision: Microsecond
TAI (International Atomic Time):
– Reference: Frequency of electromagnetic radiation from an electron
– Medium: Atomic Clock
– Accuracy: 1 second of variation every 15 billion years
Question: What time reference should be taken?
While knowing that:
– The Earth's rotation is irregular.
– There is no more accurate than an atomic clock.
It would therefore require a time repository that would have the accuracy of the IAT and that would take into account the irregularity of the Earth's rotation such as the GMT and UT time scales.
The UTC time repository has been created.
UTC – Universal Time Coordinated:
– Coordination between the IAT and GMT / UT
– Official time repository at the global level
Setting up the NTP
NTP – Network Time Protocol
– Standardized protocol
– UDP port 123
This protocol works in Customer/Server mode.
Step 1: Time zone definition
When a piece of equipment is going to interrogate an NTP server, it will recover the UTC's 0th time!! The jet lag configuration is the responsibility of the local administrator.
– Winter time – UTC -1
– Daylight saving time – UTC -2
Switch (config) - timezone clock EN 1
EN – Timezone name
1 – UTC-1
Winter time /summer time
Switch (config) - clock summer-time FR recurring last Sun Mar 2:00 last Sun Oct 3:00
last Sun Mar 2:00 – last Sunday in March at 2 a.m.
last Sun Oct 3:00 – last Sunday in October at 3 a.m.
Step 2: Set a time source
All our equipment must be synchronized. To do this they need a common time repository. the best references
This solution should only be implemented when we are in the presence of an isolated local network with no reliable time repository.
Switch (config) - clock set hh:mm:ss
Our other equipment will synchronize on the latter.
Switch (config) - ntp server X.X.X.X Switch (config) - ntp server X.X.X.X prefer
Step 3: Securent NTP
Switch (config) - ntp authentication-ke[key-number]y md5 [key-string] Switch (config) - ntp authenticate Switch (config) - ntp trusted-key [key-number] Switch (config) - ntp server X.X.X.X key [key-number]
What gives us:
Switch (config) - ntp authentication-key 10 md5 Finger Switch (config) - ntp authenticate Switch (config) - ntp trusted-key 10 Switch (config) - ntp server X.X.X.X key 10
Switch (config) - access-list 1 permit X.X.X.X X.X.X.X Switch (config) - ntp access-grou[ serve-only | serve | peer | query-only ]p 1
– serve-only – only sync queries are allowed
– serve – Sync and control queries are allowed, however our switch cannot sync its own clock
– peer – Sync and control queries are allowed, our switch can sync its own clock
– query-only – No idea …
ntp source blablabla
master ntp 5
ntp server x.x.x.x
ntp server x.x.x.x prefer
Hoping this article has been helpful to you! Don't hesitate to let me know!!
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