NTP Design

[vinovinom]

Hi 

I have question regarding NTP. Current Scenario

Physical Server(NTP Server for LAN hosts) ----- This communicates with public NTP source to get time.

New design

Cisco 4500 Switch needs to be NTP Server with the same public NTP source and LAN clients pointing towards this Switch for time.

Requirement: 

Same IP address in the physical server should be assigned in switch as NTP source address so that migration is done with minimum impact from server perspective as there are some clients hardcoded with NTP address in their systems.

I would require a solution to use the same IP address in switch. I have 2 ideas which needs some assurance from you guys.

1. Create a Loopback address with the IP adddress of the Physical server.

a) If I do this then as the Vlan that the server belongs to has SVI on the same switch with same subnet will this affect it ? and is it possible ?

b) If I do the ntp source loopback command what does it infer whether the NTP packets originate from it or this address replies for NTP requests ?

2. Create a secondary address as IP of the Phy server  in the SVI of the Vlan that the physical server belongs to . Is this possible to create secondary address as same Vlan and is it possible to that the NTP source command will use this secondary address?  Will there be any other implications if I create this secondary address.

Also what would the ideal configuartion to do this? Confirm below should be fine.

ntp server <public server>

ntp source command

is there any other command required to reply back to NTP requests ? (as there is no authentication required)

Thanks in advance for your replies.

Vin

[Leo Laohoo]

Here's a simple NTP design I found to be very easy (to implement and remember):   Whoever is the "host" of the default gateway is the NTP server for that subnet. 

You can then set DHCP Option 42 on the IP address for the PC.

[johnd2310]

Hi,

Usually it is best to run NTP on a server. That way you can can easily upgrade NTP software without having to take the whole switch down for a code upgrade.

If you really have to move NTP to the switch, then you can move server to different subnet and use loopback address with server's old ip address. Server's old svi will need to be removed as there will be ip overlap. The ntp source command will ensure that all ntp on the switch will be sourced from the loopback address

Thanks

John

Thanks

John

[Jon Marshall]

Vin

Just to add, unfortunately neither of your options will work.

Whether you try and create a loopback with the server IP or use a secondary IP the switch won't let you because it will be an address overlap.

I agree with John, and I have always used NTP on a server or a dedicated device rather than try and use a switch or router for that functionality.

Jon