(S)NTP synchronization on SG300 access switches?

Answered Question
Nov 18th, 2011

Hi,

In our network two Domain Controllers are configured as the central (S)NTP Servers. For a switch in Layer 3 mode it is quit easy to synchronise with these (S)NTP Servers. But what is actually the best approach for access switches in layer 2 mode, that are connected to the layer 3 switch? The only IP Address they have are part of the management VLAN ID 1 which is not routable. I am actually looking for something like a broadcast without having to put a NTP Server in management vLAN.

Boudewijn

I have this problem too.
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Correct Answer by rocater about 2 years 4 months ago

Is your layer 3 switch the gateway for your vlans? Vlan 1 can be routed, the only restriction to this would be if you do not have any routes for vlan1. If your NTP server and layer 2 switch points their default gateway at your layer 3 switch, the layer 3 switch can route traffic across that way.

It really depends how you have the network setup and what device is handling the routing for you on the local network.

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Average Rating: 5 (1 ratings)
rocater Fri, 11/18/2011 - 14:03

Hello Boudewijn,

You should be able to point across vlans using the layer 3 switch as a gateway for your layer 2 switch. Once you have that set you can us your servers to get the time. This setting is under Administration > Management Interface > IPv4 Interface.

wbplomp_cisco Tue, 11/22/2011 - 10:40

The layer 2 switches are configured with an IP Addres in the management VLAN ID 1, known as the default VLAN. That VLAN is not routable. Correct me if I am wrong.

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Correct Answer
rocater Tue, 11/22/2011 - 11:22

Is your layer 3 switch the gateway for your vlans? Vlan 1 can be routed, the only restriction to this would be if you do not have any routes for vlan1. If your NTP server and layer 2 switch points their default gateway at your layer 3 switch, the layer 3 switch can route traffic across that way.

It really depends how you have the network setup and what device is handling the routing for you on the local network.

wbplomp_cisco Sun, 11/27/2011 - 15:20

Problem solved. I use a default gateway on the layer 2 switches. I was surprised that the default VLAN is routable. I thought i read somewhere it was isolated. Anyway, it works. Thanks.

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Posted November 18, 2011 at 1:57 PM
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