[ntp:questions] Re: Peer Statement

Steve Kostecke kostecke at ntp.isc.org
Thu Oct 20 20:22:25 UTC 2005


On 2005-10-20, DJ <drnj at freemail.redherring.co.uk> wrote:

> You haven't answered
>
> how would server A know the difference between ServerB's ntpd talking
> to it and ServerC performing 'ntpdate ServerA' ??

It's a matter of a REQUEST FOR time vs an EXCHANGE OF time.

'ntpdate serverA' REQUESTS the time from serverA

'server serverA' tells an ntpd to REQUEST the time from serverA

'peer serverA' tells an ntpd to EXCHANGE the time with serverA

Here's what the Reference Implmentation documumentation says about
'server' and 'peer':

server

    For type s and r addresses (only), this command normally mobilizes
    a persistent client mode association with the specified remote
    server or local reference clock. IN CLIENT MODE THE CLIENT CLOCK CAN
    SYNCHRONIZE TO THE REMOTE SERVER OR LOCAL REFERENCE CLOCK, BUT THE
    REMOTE SERVER CAN NEVER BE SYNCHRONIZED TO THE CLIENT CLOCK. This
    command should NOT be used for type b or m addresses.

peer

    For type s addresses (only), this command mobilizes a persistent
    symmetric-active mode association with the specified remote peer.
    IN THIS MODE THE LOCAL CLOCK CAN BE SYNCHRONIZED TO THE REMOTE
    PEER OR THE REMOTE PEER CAN BE SYNCHRONIZED TO THE LOCAL CLOCK.
    This is useful in a network of servers where, depending on various
    failure scenarios, either the local or remote peer may be the better
    source of time. This command should NOT be used for type b, m or r
    addresses.

Address types used above:

s == a remote server or peer (IPv4 class A, B and C)
b == the broadcast address of a local interface
m == a multicast address (IPv4 class D)
r == a reference clock address (127.127.x.x)

Please see http://www.eecis.udel.edu/~mills/ntp/html/confopt.html for
more information ...

-- 
Steve Kostecke <kostecke at ntp.isc.org>
NTP Public Services Project - http://ntp.isc.org/




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