Network Time Protocol Objectives to learn how to

Network Time Protocol • Objectives – to learn how to setup ntp • Contents – – – The NTP Server What is NTP? Download and Install The NTP Package The /etc/ntp. conf File How To Get NTP Started Determining If NTP Is Synchronized Properly

What is NTP? • Network Time Protocol – – – Used to keep clock’s syncronized within your nodes Important for logservers and logfiles Transaction servers Various applications Time critic operations that needed to be syncronized • Stratum levels – Level 1 most accurate, many public exist – Level 2 next accurate, often companies timeservers – Lower levels • LW radio carriers as reference • Important atomic clock servers that supports NTP http: //www. eecis. udel. edu/~mills/ntp/servers. html

Download and Install The NTP Package • Check if NTP is there and then download it # ftp. redhat. com ftp> cd /pub/redhat/linux/9/en/os/i 386/Red. Hat/RPMS ftp> ls ntp* ftp> mget ntp* • Install NTP after it is downloaded # rpm –ivh ntp-4. 1. 2 -5. i 386. rpm • NTP is redhat standard, however it is not started. # chkconfig ntpd on # service ntpd start • First time chkconfig and service will open iptables firewall as well, ntp used port 123 UDP

The /etc/ntp. conf File • First we specify the sample servers we're interested in: – Servers are used in order, average time can be calculated server otherntp. server. org ntp. research. gov # A stratum 1 server # A srtatum 2 server • Then we restrict the type of access you allow these servers restrict otherntp. server. org mask 255 nomodify notrap noquery restrict ntp. research. gov mask 255 nomodify notrap noquery • Declare the networks this NTP server should serve restrict 192. 168. 0. 0 mask 255. 0 notrust nomodify notrap restrict 192. 168. 1. 0 mask 255. 0 notrust nomodify notrap • This NTP server should serve itself unrestricted restrict 127. 0. 0. 1

How To Get NTP Started • To get NTP configured to start at boot: # chkconfig ntpd on – The demon is called ntpd • To start/stop/restart NTP after booting: # service ntpd start # service ntpd stop # service ntpd restart • If you like with init scripts: # /etc/init. d/ntpd start # /etc/init. d/ntpd stop # /etc/init. d/ntpd restart • Logging in /var/log/messages • Logging in /var/log/ntpd. log

Testing And Troubleshooting NTP • Verifying NTP is Running # pgrep ntpd –you should get a response of plain old process ID numbers • Doing An Initial Synchronization against one server –First check current idea of time –Then syncronize against NTP server # date Thu Sep 7 00: 00 PDT 2004 # ntpdate –u ntp. research. gov Looking for host ntp. research. gov and service ntp host found : ntp. research. gov 7 Sep 08: 03: 38 ntpdate[2472]: step time server ntp. research. gov offset 28993. 084943 sec # date Sep 7 08: 03: 38 PDT 2004 –Last check that time was adjusted –If time it was to big difference in time you might want to set the time as exact you can manually and do the sync again

Determining If NTP Is Synchronized Properly • With ntpq command see the servers you sync with # ntpq -p remote refid st t when poll reach delay offset jitter ======================================= -jj. cs. umb. edu gandalf. sigmaso 3 u 95 1024 377 31. 681 -18. 549 1. 572 milo. mcs. anl. go ntp 0. mcs. anl. go 2 u 818 1024 125 41. 993 -15. 264 1. 392 -mailer 1. psc. edu ntp 1. usno. navy. 2 u 972 1024 377 38. 206 19. 589 28. 028 -dr-zaius. cs. wis ben. cs. wisc. edu 2 u 502 1024 357 55. 098 3. 979 0. 333 +taylor. cs. wisc. ben. cs. wisc. edu 2 u 454 1024 347 54. 127 3. 379 0. 047 -ntp 0. cis. strath harris. cc. strat 3 u 507 1024 377 115. 274 -5. 025 1. 642 *clock. via. net. GPS. 1 u 426 1024 377 107. 424 -3. 018 2. 534 ntp 1. conectiv. c 0. 0 16 u - 1024 0 0. 000 4000. 00 • Jitter should be less than 100 • Try to use NTP server close to you with high strata level

Your Linux NTP clients cannot Synchronize Properly • Your test show something like this # ntpq -p remote refid st t when poll reach delay offset jitter ======================================= LOCAL(0) 10 l 64 7 0. 000 0. 008 ntp-cup. externa 0. 0 16 u 64 0 0. 000 4000. 00 snvl-smtp 1. trim 0. 0 16 u 64 0 0. 000 4000. 00 nist 1. aol-ca. tr 0. 0 16 u 64 0 0. 000 4000. 00 • This could be caused by the following – Older versions of NTP must have IP addresses, not FDQN – A firewall blocking access to your Stratum 1 and 2 NTP servers, port 123 UDP must be opened. – Fedora Core 2 syncing to Feodora 2 client has a known bug

Fedora / Red. Hat File Permissions • The /etc/ntpd catalog must have correct owner and group chown ntp: ntp /etc/ntp This catalog holds the drift file and network delay correction!

Configuring Cisco Devices To Use An NTP Server • Cisco IOS ciscorouter> enable password: ***** ciscorouter# config t ciscorouter(config)# ntp update-calendar ciscorouter(config)# ntp server 192. 168. 0. 10 ciscorouter(config)# ntp server 192. 168. 1. 201 ciscorouter(config)# exit ciscorouter# wr mem • ntp server: Forms a server association with another system. • ntp update-calendar: Configures the system to update its hardware clock from the software clock at periodic intervals.

Configuring Cisco Devices To Use An NTP Server • CAT OS ciscoswitch> enable password: ***** ciscoswitch# set ntp client enable ciscoswitch# ntp server 192. 168. 0. 10 ciscoswitch# ntp server 192. 168. 1. 201 ciscoswitch# exit • ntp server: Forms a server association with another system. • set ntp client enable: Activate the NTP client

Summary • • • NTP server is adjust time and date on nodes Configuration sit in /etc/ntpd. conf Calibration files sit in /etc/ntpd/ Strata levels tells system accuracy Strata level 1 is most accurate Stratalevel 2 is next accurate Many applications rely on exact time NTPD is the name of client and server demon Show ntp status with ntpq –p Update time manually: ntpdate –u ntp. research. gov Most routers/Switches has NTP timesettings