From: Anderson Mota Alves (mota_anderson@hotmail.com)
Date: Fri Feb 10 2006 - 07:48:00 GMT-3
Hi,
From my point of view when cisco says how many NTP "hops" it means how
far away you machine is from an authoritative time source (NTP stratum of
1) so imagine you see your NTP client side with a stratum of 3 it means
that you are 2 "NTP hops" away from the authoritative time source and not
that you are 2 routings hops away from that machine.
Imagine you have 3 machines one as a server and 2 as clients, you
configure one as authoritative server with command "ntp master 1", the
2nd machine as client ("ntp server x.x.x.x") "putting the ip address of
the authoritative server" and for the 3rd machine you configure as a ntp
peer of the 2nd machine with command: ntp peer "x.x.x.x" putting the ip
address of the 2nd machine.
Configuring that you can see with "show ip ntp associations" the stratum
they are receiving, on the 3rd machine you should get a stratum of 3
since it's getting the time from 2nd machine (which has stratum of 2) and
1st machine as an authoritative server (with stratum of 1 - being the
most accurate server) so that's the concept I have for "NTP hops",
someone please correct me if I'm wrong.
Regards,
Andy
PS:
NTP uses the concept of a "stratum" to describe how many NTP "hops" away
a machine is from an authoritative time source. A "stratum 1" time server
typically has an authoritative time source (such as a radio or atomic
clock, or a GPS time source) directly attached, a "stratum 2" time server
receives its time via NTP from a "stratum 1" time server, and so on.
------------------------------------------------------------------------
From: Saad Adam <subjectvsobject@yahoo.com>
Reply-To: Saad Adam <subjectvsobject@yahoo.com>
To: Anderson Mota Alves <mota_anderson@hotmail.com>,
sameer.azam@gmail.com
CC: ccielab@groupstudy.com
Subject: Re: NTP Quesion
Date: Fri, 10 Feb 2006 02:26:57 -0800 (PST)
>Hi,
> Strantum increments with the number of hop counts. The topolog is
a bit confusing, If R4 is the NTP server with a stratum of 2 then all
the directly connected peers will have a hop count of 1, and that is
used to increment the stratum on them making it statum 3. If a peer
is 2 hops away, then the statum will be 2(Server statum) + 2(for the
hops)= 4 statrum.
>
> There are cases where a device is more than 5 hops away, from the
ntp server and the question will ask u to have a stratum of lets say
3, which at first site might seem impossible in that case u might
consider using a gre tunnel to reduce the hop counts.
>
> Good luck.
> Saad.
>
>Anderson Mota Alves <mota_anderson@hotmail.com> wrote:
> I also suggest you to always set the clock set on the routers
before
>configure ntp with command "clock set" since the machines will be
using
>the hardware clock beforing establishing synchronization with
server.
>
>And I forgot to mention you that I think you can't configure a 3550
as
>master so use a router as an example for that othewise you won't
have the
>command ntp master available, but I may be wrong on this.
>
>Does anybody know if ntp master is supported on 3550 switches with
newer
>IOS or it's not supported at all?
>
>Regards,
>
>Andy
>
>--------------------------------------------------------------------
>
>From: sameer azam
>To: Anderson Mota Alves
>Subject: Re: NTP Quesion
>Date: Thu, 9 Feb 2006 14:33:44 +0400
>
>hi,Do u mean that when u configure R1 as the MASTER with a stratum
of
>2 then automatically other ( SW & R4) will set their stratum value
to
>3. See i understand the stratum concept and that is no more than
this
>that lower the value better the stratum is. but when when asked to
>configure the A SECIFIC Stratum value on R4 & Sw do u need to
>configure that or not?and also there is no NTP MASTER command on the
>CAT 3550. so in this what should be the correct answer. Regards
>
>On 2/9/06, Anderson Mota Alves wrote:
>
>Hi Sameer,
>
>Since you need to have the clients with a stratum of 3 in order
>to accomplish that you need to configure the server with a
>stratum of 2, so in this case the clients will be getting the
>stratum with a value of 3.
>
>Solution:
>
>SW: loopback 0's SW: 12.12.7.7
>ntp server 12.12.1.1
>ntp source loopback 0
>
>R4: loopback 0's R4: 12.12.4.4
>ntp server 12.12.1.1
>ntp source loopback 0
>
>R1: (the server) Loopback 0's R1: 12.12.1.1
>ntp master 2
>ntp source loopback 0
>
>Note that I haven't configured any stratum value on SW since this
>router will
>be getting this value from the server (R1)
>
>If you have a way to set this up please do it and then let me
>know if everything worked fine.
>
>Regards,
>
>Andy
>
>------------------------------------------------------------
>
>From: Ivan
>Reply-To: Ivan
>To: ccielab@groupstudy.com, sameer azam
>Subject: Re: NTP Quesion
>Date: Thu, 9 Feb 2006 11:56:47 +0300
> >lake(config)#ntp master ?
> > <1-15> Stratum number
> >
> >
> > > The topology is like follows;
> > >
> > > SW
> > >
> > >
> > >
>R1______---_______R4
> > >
> > > The link between R1 & Sw is Ethernet connection.
> > > The link between R1 & R4 is Frame-Relay Connection.
> > >
> > > The QUESTION IS;
> > >
> > > You need to configure the R4 & SW for STRATUM 3
> > > Both of R4 & SW should get get their time clock from the
>R1.
> > >
> > > How would you do this?
> > >
> >
> >--
> >Ivan
> >
>
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