From the 3750 configuration guide
The switch does not have a hardware-supported clock and cannot function as an NTP master clock to which peers synchronize themselves when an external NTP source is not available. The switch also has no hardware support for a calendar. As a result, the ntp update-calendar and the ntp master global configuration commands are not available.
So no to the 3750.
Unfortunately the pix cannot do this either.
Jon is correct that the 3750 can not generate accurate NTP time on its own (no outside source) because of the limitations listed. I am not clear from your post whether you need it to operate completely independently or whether there is a possibility that the 3750 could learn time from some source (perhaps an NTP source on the Internet). If the 3750 can learn time then I believe that it could function as NTP server for other devices in the network.
It's exactly that you wrote what I need. Cisco Pix and Cisco 3750 can learn time by NTP from an external server but I also should need that at least one of them could act as NTP server for other devices in the network. Do you think it's possible?
As usual Rick is correct in what he says. You cannot use the 3750 as a master but it looks like you can use it as an NTP server for other devices. I don't have 3750 in lab but i do have 3560 and it has the same caveats as 3750 so i thought i'd test it
3560 lab switch synched to a ntp server
lab_sw1#sh ntp status
Clock is synchronized, stratum 3, reference is 10.15.1.11
nominal freq is 119.2092 Hz, actual freq is 119.2087 Hz, precision is 2**18
reference time is CA4ADE46.7735F706 (07:09:58.465 UTC Fri Jul 20 2007)
clock offset is 15.4096 msec, root delay is 42.42 msec
root dispersion is 36.29 msec, peer dispersion is 4.84 msec
3550 lab switch synched to the 3560
HQ-FTZ-F00-SW1#sh ntp status
Clock is synchronized, stratum 4, reference is 10.15.1.4
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**18
reference time is CA4ADDF9.1E5EEED1 (07:08:41.118 UTC Fri Jul 20 2007)
clock offset is 0.3215 msec, root delay is 48.74 msec
root dispersion is 15904.91 msec, peer dispersion is 15875.02 msec
thank you for you reply. So you mean that your 3550 is synched with your 3560? Ok I'll test my 3750 in the same way. Any idea about the Cisco PIX?
I started configuring my 3750 with this command:
ntp server a.b.c.d
but I get this result from show ntp status:
Clock is unsynchronized, stratum 16, no reference clock
nominal freq is 119.2092 Hz, actual freq is 119.2082 Hz, precision is 2**17
reference time is 00000000.00000000 (01:00:00.000 CET Mon Jan 1 1900)
clock offset is 0.1575 msec, root delay is 0.00 msec
root dispersion is 0.00 msec, peer dispersion is 0.09 msec
what could be the problem?
Number of things
1) Do you have any firewalls in between your 3750 and the time source
2) Do you have any authentication turned on on your ntp master/server.
3) Presumably you can ping the ntp server/master ?
1. Yes I do. there is a cisco PIX between 3750 and ntp server, but NTP packets from inside to outside are allowed in the configuration
2.there is no authentication. NTP server is a public server.
3. Yes i can ping NTP server from 3750
Are you sure that the source ip address being used by the switch for it's ntp is the same IP address that is allowed through your firewall.
You can use the command
ntp source "interface" to set the source interface on your switch.