## Time Synchronization

BWCTL works best when the clocks of the clients and servers are synchronized. If the hosts are not synchronized, they might try to begin tests at different times.

NTP is a protocol used to synchronize a computer's clock to clocks available over a network. The NTP software is available for, and often times, included with many operating systems. Most Unix systems use the reference implementation of the software, and the example included with this howto is geared to that version.

ntp.org has some advice for selecting NTP servers. However, there are some general rules of thumb to follow for NTP configuration. The NTP configuration should include between 4 and 7 NTP clocks with which it will try to synchronize. By including this number of servers, the NTP software can make better decisions about which clocks are accurate and who it should trust for time data. The NTP servers should be in close proximity to the host, though this is not a hard requirement. Ideally, the network paths to the servers should differ as much as possible from each other.

There are a large number of public NTP servers. There's a list available at http://support.ntp.org/bin/view/Servers/WebHome.

Internet2 maintains a set of NTP servers that can be used if the host is connected to the Internet2 network.

- owamp.atla.net.internet2.edu - Atlanta, GA
- owamp.chic.net.internet2.edu - Chicago, IL
- owamp.hous.net.internet2.edu - Houston, TX
- owamp.losa.net.internet2.edu - Los Angeles, CA
- owamp.kans.net.internet2.edu - Kansas City, MO
- owamp.salt.net.internet2.edu - Salt Lake City, UT
- owamp.newy.net.internet2.edu - New York, NY

### Example NTP /etc/ntp.conf file

    # /etc/ntp.conf, configuration for ntpd
    logfile /var/log/ntpd
    driftfile /var/lib/ntp/ntp.drift
    statistics loopstats peerstats clockstats
    filgen loopstats file loopstats type day enable
    filgen peerstats file peerstats type day enable
    filgen clockstats file clockstats type day enable

    server owamp.chic.net.internet2.edu iburst
    server owamp.hous.net.internet2.edu iburst
    server owamp.kans.net.internet2.edu iburst
    server owamp.losa.net.internet2.edu iburst
    server owamp.newy.net.internet2.edu iburst