I have a endpoint which is on vlan x and a SNTP server on vlan Y of same cisco switch. I am trying to synchronize my time from SNTP server. endpoint is able to resolve ARP and get the mac of SNTP server but not able to ping/connect to SNTP server. I don't understand why the endpoint is not able to synchronize time from SNTP server, i could not see NTP packets from endpoint.

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    something is wrong here, if endpoint and SNTP server are in separate VLAN, endpoint should not get SNTP server MacAddress , but the router MAC. How are your vlan interconnected?
    – JFL
    Feb 15, 2017 at 10:46
  • You are going to need to provide more information. For example, a better description of the network, and the network device models and configurations. If you can ARP from one VLAN to another, something is terribly wrong with your topology and/or configurations.
    – Ron Maupin
    Feb 15, 2017 at 14:48
  • @RonMaupin MY SNTP server is tagged in both the VLAN, so endpoint is able to get MAC address of the NSTP server, but not able to communicate over layer 3. Feb 16, 2017 at 4:10
  • You have a trunk to the server, and the server has an address in both VLANs? That is not what the question says: "a SNTP server on vlan Y." You should post a diagram and network device configurations. I think you may have a misunderstanding of how this works. When a host need to communicate via layer-3 to another host on a different layer-3 network, it must go through its configured gateway.
    – Ron Maupin
    Feb 16, 2017 at 4:14
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Aug 16, 2017 at 22:49

3 Answers 3


If the addresses are on different vlans it means that you have a router between them, therefore MAC address is the gateway address, not the destination.


You need to verify the MAC address of the ARP response you get for the SNTP server. Determine if it's the MAC of the server, or the MAC of the default gateway.

Also check the IP configuration settings on both hosts, and both the vlans. The symptoms are similar to an IP configuration issue.


Since you have refused to provide the requested information that we need to correctly answer your question, and based on your comment, it sounds like you are leaking both layer-2 LANs to the SNTP server, but that doesn't help you with the layer-3 network.

Your host (endpoint), with an address on VLAN X, is trying to communicate with another host (the server), with an address on VLAN Y. The addresses are on different layer-3 networks. A host will use ARP to resolve a layer-3 address to a layer-2 address if both host addresses are on the same layer-3 network. If the destination host is on a different layer-3 network, the source host will use the layer-2 address of its configured gateway. Traffic between different layer-3 addresses must go through a router (the host's configured gateway).

That applies to both hosts in a bidirectional protocol.

If you want a server to be directly connected to both VLANs, you need the switch to trunk both VLANs to the server, and the server interface must be configured as a trunk, and the server must have an address in each VLAN. How you configure the server for that is off-topic here.

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