what is the diffence between ntp master, server and peer?

[dolanduck.]

i am confused ? how does it work ?

[Mark Malone · Accepted solution]

Hi in short

ntp server 

points to a server to get its time

ntp peer

gets its ntp off an actual peer device like another router on the network

ntp master

Configures the device as an authoritative NTP server.

[dolanduck.]

so for peer if i have a router with the time set manually i can use the

peer

command so it get its time from router i set manually? and is it possible to have two ntp servers on a network ?

[Julio E. Moisa]

Yes, you can have 2 or more NTP Servers, and from the client perspective use the parameter "prefer" at the end to select primary NTP Server. 

[Julio E. Moisa]

Hi,

NTP Master is used to indicate the NTP Server (Authoritative NTP) and its type of stratum, the stratum 1 is used for public NTP Servers, so if you set up one router as NTP Server it could be stratum 2. The NTP Clients will be NTP Stratum 3.

NTP server is configured on the client NTP Routers to indicate the IP Address of NTP Server in order to obtain all the time information.

NTP Peer is configured in order to sync the time settings with other router. You can specify multiple peer associations. 

Hope it is useful.

[Jaderson Pessoa]

Hello,
I would start by reviewing some basic concepts:

- ntp server is based on a client to server relationship.

- ntp peer is based on a peer to peer relationship.

In configuring ntp server the client will always ask for time from the server and the server will never ask for time from the client.

In configuring ntp peer both peers may attempt to learn time from the other and each peer may offer its time to the other.

So if you are configuring ntp on a router (or switch) I would suggest that these are some questions that will guide you to the correct relationship:

- is the other device always going to be authoritative for ntp? If so then the appropriate relationship is client to server. Your router (or switch) will always ask for time from the server but will never offer time to the server.

- is the other device sometimes authoritative and sometimes not authoritative? If so then the appropriate relationship is peer to peer.

Let me suggest an example which may clarify the functions.

- let us consider router A and router B.

- let us assume that router A will learn time from Internet server 1.

- let us assume that router B will learn time from Internet server 2.

Then the appropriate configuration of router A has server 1 as ntp server and has router B as ntp peer.

Also router B has server 2 as ntp server and has router A as ntp peer.

The result is this:

- as long as router A is in sync with server 1 it will not need to ask router B for time. But if for some reason it loses its sync with server 1 then router A will attempt to learn time from router B. And as long as router B is in sync with its server 2 then it will send its time to router A.

as long as router B is in sync with server 2 it will not need to ask router A for time. But if for some reason it loses its sync with server 2 then router B will attempt to learn time from router A. And as long as router A is in sync with its server 1 then it will send its time to router B.

Check it for more detail: https://community.cisco.com/t5/switching/ntp-peer/td-p/2091646

[Richard Burts]

I would offer a slightly different perspective in answering this question. In configuring ntp on an IOS device there are several things that we can specify: who has authoritative ntp time? Is the device we are configuring going to learn ntp time and if so from what device will it learn ntp time? Is this device going to send ntp time to other devices? 

When we configure ntp master we are asserting that this device has authoritative ntp time. It does not specify how this device learned its time. It implies that this device will send ntp time to other devices who request it.

When we configure ntp server we are stating that we believe that the device identified in the command knows authoritative ntp time and this device will learn ntp time from that device.

When we configure ntp master or ntp server we are specifying a server relationship or a client relationship. When we configure ntp peer we are not specifying either server or client relationship. In the ntp peer relationship we would offer ntp time to the peer if we know authoritative ntp time and the peer would offer ntp time to us if the peer knows authoritative ntp time.

HTH

Rick