Network Time Protocol - NTP

The ntpd daemon running on the switch implements the NTP protocol. It synchronizes the system time with time servers in the /etc/ntpsec/ntp.conf file. The ntpd daemon starts at boot by default.

Configure NTP Servers

The default NTP configuration includes the following servers, which are in the /etc/ntpsec/ntp.conf file:

• server 0.cumulusnetworks.pool.ntp.org iburst
• server 1.cumulusnetworks.pool.ntp.org iburst
• server 2.cumulusnetworks.pool.ntp.org iburst
• server 3.cumulusnetworks.pool.ntp.org iburst

To add the NTP servers you want to use, run the following commands. Include the iburst option to increase the sync speed.

cumulus@switch:~$ nv set service ntp default server 4.cumulusnetworks.pool.ntp.org iburst on
cumulus@switch:~$ nv config apply

cumulus@switch:~$ sudo nano /etc/ntpsec/ntp.conf
# pool.ntp.org maps to about 1000 low-stratum NTP servers.  Your server will
# pick a different set every time it starts up.  Please consider joining the
# pool: <http://www.pool.ntp.org/join.html>
server 0.cumulusnetworks.pool.ntp.org iburst
server 1.cumulusnetworks.pool.ntp.org iburst
server 2.cumulusnetworks.pool.ntp.org iburst
server 3.cumulusnetworks.pool.ntp.org iburst
server 4.cumulusnetworks.pool.ntp.org iburst

To verify that ntpd is running on the system:

cumulus@switch:~$ ps -ef | grep ntp
ntp       4074     1  0 Jun20 ?        00:00:33 /usr/sbin/ntpd -p /var/run/ntpd.pid -g -u 101:102

To check the NTP peer status:

cumulus@switch:~$ nv show service ntp mgmt server
                 delay    iburst  jitter  offset   peer-state  poll  reach  refid         stratum  type  when
---------------  -------  ------  ------  -------  ----------  ----  -----  ------------  -------  ----  ----
23.157.160.168   67.4257          2.3843  -3.9378  -           128   377    129.6.15.28   2        u     41  
50.205.57.38     72.6007          1.0799  -1.8208  *           128   377    .GPS.         1        u     63  
h134-215-155-17  59.4988          2.3081  -2.6286  +           128   377    216.239.35.0  2        u     15  
li1150-42.membe  40.9645          0.4877  -1.9565  +           64    376    129.7.1.66    2        u     162

cumulus@switch:~$ ntpq -p
      remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
+ec2-34-225-6-20 129.6.15.30      2 u   73 1024  377   70.414   -2.414   4.110
+lax1.m-d.net    132.163.96.1     2 u   69 1024  377   11.676    0.155   2.736
*69.195.159.158  199.102.46.72    2 u  133 1024  377   48.047   -0.457   1.856
-2.time.dbsinet. 198.60.22.240    2 u 1057 1024  377   63.973    2.182   2.692

The following example commands remove some of the default NTP servers:

cumulus@switch:~$ nv unset service ntp default server 0.cumulusnetworks.pool.ntp.org
cumulus@switch:~$ nv unset service ntp default server 1.cumulusnetworks.pool.ntp.org
cumulus@switch:~$ nv unset service ntp default server 2.cumulusnetworks.pool.ntp.org
cumulus@switch:~$ nv unset service ntp default server 3.cumulusnetworks.pool.ntp.org
cumulus@switch:~$ nv config apply

cumulus@switch:~$ sudo nano /etc/ntpsec/ntp.conf
...
# pool.ntp.org maps to about 1000 low-stratum NTP servers.  Your server will
# pick a different set every time it starts up.  Please consider joining the
# pool: <http://www.pool.ntp.org/join.html>
server 4.cumulusnetworks.pool.ntp.org iburst
...

Specify the NTP Source Interface

By default, the source interface that NTP uses is eth0. The following example command configures the NTP source interface to be swp10.

cumulus@switch:~$ nv set service ntp default listen swp10
cumulus@switch:~$ nv config apply

cumulus@switch:~$ sudo nano /etc/ntpsec/ntp.conf
...
# Specify interfaces
interface listen swp10
...

Use NTP in a DHCP Environment

You can use DHCP to specify your NTP servers. Ensure that the DHCP-generated configuration file /run/ntp.conf.dhcp exists. The /etc/dhcp/dhclient-exit-hooks.d/ntp script generates this file, which is a copy of the default /etc/ntpsec/ntp.conf file with a modified server list from the DHCP server. If this file does not exist and you plan on using DHCP in the future, you can copy your current /etc/ntpsec/ntp.conf file to the location of the DHCP file.

To use DHCP to specify your NTP servers, run the sudo -E systemctl edit ntpsec.service command and add the ExecStart= line:

cumulus@switch:~$ sudo -E systemctl edit ntpsec.service
[Service]
ExecStart=
ExecStart=/usr/sbin/ntpd -n -u ntp:ntp -g -c /run/ntp.conf.dhcp

To validate that your configuration, run these commands:

cumulus@switch:~$ sudo systemctl restart ntp
cumulus@switch:~$ sudo systemctl status -n0 ntpsec.service

If the state is not Active, or the alternate configuration file does not appear in the ntp command line, it is likely that you made a configuration mistake. Correct the mistake and rerun the commands above to verify.

Configure NTP with Authorization Keys

For added security, you can configure NTP to use authorization keys.

Configure the NTP Server

1. Create a .keys file, such as /etc/ntp.keys. Specify a key identifier (a number between 1 and 65535), an encryption method (M for MD5), and the password. The following provides an example:

   #
   # PLEASE DO NOT USE THE DEFAULT VALUES HERE.
   #
   #65535  M  akey
   #1      M  pass
   
   1  M  CumulusLinux!
   

2. In the /etc/ntpsec/ntp.conf file, add a pointer to the /etc/ntp.keys file you created above and specify the key identifier. For example:

   keys /etc/ntp/ntp.keys
   trustedkey 1
   controlkey 1
   requestkey 1
   

3. Restart NTP with the sudo systemctl restart ntp command.

Configure the NTP Client

The NTP client is the Cumulus Linux switch.

1. Create the same .keys file you created on the NTP server (/etc/ntp.keys). For example:

   cumulus@switch:~$  sudo nano /etc/ntp.keys
   #
   # DO NOT USE THE DEFAULT VALUES HERE.
   #
   #65535  M  akey
   #1      M  pass
   
   1  M  CumulusLinux!
   

2. Edit the /etc/ntpsec/ntp.conf file to specify the server you want to use, the key identifier, and a pointer to the /etc/ntp.keys file you created in step 1. For example:

   cumulus@switch:~$ sudo nano /etc/ntpsec/ntp.conf
   ...
   # You do need to talk to an NTP server or two (or three).
   #pool ntp.your-provider.example
   # OR
   #server ntp.your-provider.example
   
   # pool.ntp.org maps to about 1000 low-stratum NTP servers.  Your server will
   # pick a different set every time it starts up.  Please consider joining the
   # pool: <http://www.pool.ntp.org/join.html>
   #server 0.cumulusnetworks.pool.ntp.org iburst
   #server 1.cumulusnetworks.pool.ntp.org iburst
   #server 2.cumulusnetworks.pool.ntp.org iburst
   #server 3.cumulusnetworks.pool.ntp.org iburst
   server 10.50.23.121 key 1
   
   #keys
   keys /etc/ntp.keys
   trustedkey 1
   controlkey 1
   requestkey 1
   ...
   

3. Restart NTP in the active VRF (default or management). For example:

   cumulus@switch:~$ systemctl restart ntp@mgmt.service
   

4. Wait a few minutes, then run the ntpq -c as command to verify the configuration:

   cumulus@switch:~$ ntpq -c as
   
   ind assid status  conf reach auth condition  last_event cnt
   ===========================================================
     1 40828  f014   yes   yes   ok     reject   reachable  1
   

   After a successful authorization, you see the following command output:

   cumulus@switch:~$ ntpq -c as
   
   ind assid status  conf reach auth condition  last_event cnt
   ===========================================================
     1 40828  f61a   yes   yes   ok   sys.peer    sys_peer  1
   

Considerations

NTP in Cumulus Linux uses the /usr/share/zoneinfo/leap-seconds.list file, which expires periodically and results in generated log messages about the expiration. When the file expires, update it from https://www.ietf.org/timezones/data/leap-seconds.list or upgrade the tzdata package to the newest version.

Related Information

• NTP website
• Wikipedia - Network Time Protocol
• Debian wiki - NTP