Red Hat Summit第4章 Overview of Network Time Security (NTS) in chrony
Network Time Security (NTS) is an authentication mechanism for Network Time Protocol (NTP), designed to scale substantial clients. It verifies that the packets received from the server machines are unaltered while moving to the client machine. Network Time Security (NTS) includes a Key Establishment (NTS-KE) protocol that automatically creates the encryption keys used between the server and its clients.
NTS is not compatible with the FIPS and OSPP profile. When you enable the FIPS and OSPP profile, chronyd that is configured with NTS can abort with a fatal message. You can disable the OSPP profile and FIPS mode for chronyd service by adding the GNUTLS_FORCE_FIPS_MODE=0 setting to the /etc/sysconfig/chronyd file.
4.1. Enabling Network Time Security (NTS) on a client
By default, Network Time Security (NTS) is not enabled. You can enable NTS in the /etc/chrony.conf file.
Prerequisites
- The time server supports NTS.
Procedure
Edit the /etc/crony.conf file, and make the following changes:
Specify the server with the
ntsoption in addition to theiburstoption.For example: server time.example.com iburst nts server nts.netnod.se iburst nts server ptbtime1.ptb.de iburst ntsAdd the following setting to avoid repeating the Network Time Security-Key Establishment (NTS-KE) session during system boot:
ntsdumpdir /var/lib/chronyIf present, comment out or remove the following setting to disable synchronization with Network Time Protocol (NTP) servers provided by
DHCP:sourcedir /run/chrony-dhcpRestart the
chronydservice:systemctl restart chronyd
Verification
Verify if the
NTSkeys were successfully established:# chronyc -N authdata Name/IP address Mode KeyID Type KLen Last Atmp NAK Cook CLen ================================================================ time.example.com NTS 1 15 256 33m 0 0 8 100 nts.netnod.se NTS 1 15 256 33m 0 0 8 100 ptbtime1.ptb.de NTS 1 15 256 33m 0 0 8 100The
KeyID,Type, andKLenshould have non-zero values. If the value is zero, check the system log for error messages fromchronyd.Verify the client is making NTP measurements:
# chronyc -N sources MS Name/IP address Stratum Poll Reach LastRx Last sample ========================================================= time.example.com 3 6 377 45 +355us[ +375us] +/- 11ms nts.netnod.se 1 6 377 44 +237us[ +237us] +/- 23ms ptbtime1.ptb.de 1 6 377 44 -170us[ -170us] +/- 22msThe
Reachcolumn should have a non-zero value; ideally 377. If the value rarely gets 377 or never gets to 377, it indicates that NTP requests or responses are getting lost in the network.
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