Giuseppe Larosa Wed, 07/15/2009 - 04:39

Hello Ersin,

switch has to use the NTP master command but you should sync it with a NTP source for example over the internet.

all other devices will have

ntp server

Some old routers like C4700 had an on board calendar and are handy for this

be aware that NTP sync requires time (minutes)

and udp port 123 needs to be permitted

Hope to help


ergonullu Wed, 07/15/2009 - 04:55

I did not get the ntp source part.May I use the core switch as a source ? What command needs to be typed on that switch

Richard Burts Wed, 07/15/2009 - 05:08


If you configure your core switch to learn NTP time from some external source of NTP then your core switch can function as an NTP server to the other devices in your network. If your core switch does not learn NTP time from an external source then you can configure it to function as an NTP server by configuring it as ntp master. The commands that you would type vary depending on whether your core switch is CatOS or IOS. Which is it?



ergonullu Wed, 07/15/2009 - 05:26

My core switch has IOS.I do not know which source to use ? Domain controller maybe but how ?

vmiller Wed, 07/15/2009 - 06:52

There is probably nothing in your server/switch environment that will function as a good NTP server, their clocks aren't accruate enough. You need a stratum 2 or stratum 1 source. Here is one of may lists of Public NTP servers.

You allow the port in, and synch to that. then your "inside" server can provide NTP to the rest of your network. See Guiseppes example above (he is never wrong)

more light reading:

IOS config guide:

ergonullu Wed, 07/15/2009 - 07:45

Basicly what I did and worked

Go to core switch

-set time and date by "clock" command

-type ntp master command

-Go to edge switches and type

-ntp server

ıf you have vlans type vlan default

gateways for the IP address.

Only thing this is manual system make sure your core switch works fine :)



ergonullu Wed, 07/15/2009 - 07:57

One thing is interesting that I wanted to share ....

I defined my core switch as a ntp master

my 2 dist switches also using coreswitch for getting clock info.VLANs which were defined on dist switches connected to some edge switches.When I type

ntp server vlandefaultgatewway

it works but funny thing is that ;

that VLAN defined on dist switch even dist switch is not ntp master edge switches are getting the time from dist switches or core switch ????

vmiller Wed, 07/15/2009 - 08:52

keep in mind, your clock is only as good as your source.

ergonullu Wed, 07/15/2009 - 22:32

But as I said ;

I did not get how did it happen ?

ntp master is my core

edge switches connected to Dist switch and VLANs are defined on Dist switches and on edge switches I typed

ntp server

So even the server is Core switch edge switches get the clock from Dist switches ? any idea ?




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