Network Time Protocol NTP is a protocol to synchronize time on network of machines.This is done getting time from an authoritative time source such as Atomic Clock or Radio clock attached to the time server.This time is then distributed across the network and this is being done so efficiently where in a network having 2 devices will have the time updated to the accuracy of within a millisecond of one another.NTP runs on UPD which in turn run on IPv4.
NTPv4 is an extension to the current NTPv3 where it supports both IPv4 and IPv6 and is backward compatible with NTPv3. Some of main features of NTPv4 are discussed here:
NTPv4 extends its support for IPv6 there by enabling NTP time synchronization possible over IPv6.Unlike NTPv3 which uses IPv4 broadcast message to send and receive clock updates, the NTPv4 for IPv6 uses IPv6 Multicast multicast messages for synchronization of clocks.
NTPv4 uses Symmetric Key Authentication which provides a strong cryptographic authentication mechanism which efficiently prevents the local router from being wrongly updated with incorrect time by any intruder. In this NTP symmetric Key Authentication, the keys are distributed manually on the NTP devices across the network.Note that NTPv4 group functionality supports both IPv6 named access list and IPv4 numbered access list.
DNS Support For IPv6
In NTPv3, the host names are resolved in to IPv4 addresses and the resolved IPv4 addresses are kept in memory stored in NVRAM but the host names are lost.In case of NTPv4, the host names are also stored in memory so that it can be readable and the configurations saved with host names are still readable by NTPv3.
How to Configure NTPv4 in IPv6
In Configuration mode:
To enable the client software clock to be synchronized by the NTP time server, use the command ntp server <IPv6 address> version 4
To configure the symmetric active mode where the clients will be able to synchronize the time from its peer use the command
ntp peer <IPv6 address of the peer> version 4
In order to enable NTPv4 authentication, configure the below commands
ntp authenticate enables NTPv4 authentication
ntp authentication-key numbermd5 valuedefines authentication key for NTPv4.
ntp trusted-keykey-number authenticates the identity of a system to which NTPv4 will synchronize
Useful Show Commands
The following show commands can be used to display the cache content and cache statistics
show clock <detail>
This command displays the date and time from the system software clock and the keyword
is used to check the clock source i.e. through NTP or hardware clock etc..Example:
Router> show clock detail *12:40:55.911 PST Thu Nov 29 2012 Time source is NTP
Router#show ntp status Clock is synchronized, stratum 8, reference is 127.127.1.1 nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**24 reference time is D461D902.5B2530A4 (12:52:18.356 PST Thu Nov 29 2012) clock offset is 0.0000 msec, root delay is 0.00 msec root dispersion is 937.73 msec, peer dispersion is 937.67 msec loopfilter state is 'CTRL' (Normal Controlled Loop), drift is 0.000000000 s/s system poll interval is 16, last update was 5 sec ago.
Note: To debug various NTP functions such as authentication validity and ntp events use the command debug ntp.
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