It is a basic question.

Assume 2 physical machines in two different subnets. VxLAN is configured on 2 TOR switches housing these machines in different subnets in different racks.

Host A    IP: IP-A    Mac: Mac-A

Host B    IP: IP-B    Mac: Mac-B

When A wants to talk to B, since VxLAN learns the mac addresses somehow (multicast/unicast),

  1. Can host A get the mac address of B from the local TOR switch's ARP table?
  2. When host A wants to talk to some random machine, say C (which is not a part of VxLAN), is there any special gateway IP or the same gateway IP is enough. In otherwords, when VxLAN is configured in switches do I need any special configuration in the server in terms of gateway IP or routes so as to go outside of the network?
  • A MAC address is only relevant on the LAN where it is connected. It is used by the layer-2 headers to deliver traffic on the LAN, but the layer-2 headers are stripped off when sending to a different LAN.
    – Ron Maupin
    Jun 21, 2016 at 16:31
  • Ron, In the context of vxlan, the remote mac is available in the local switch but I am not sure it is populated in the switch's arp table.
    – user88975
    Jun 21, 2016 at 16:44
  • Switches have MAC address tables, but they don't get involved in ARP or maintain ARP tables the way hosts do.
    – Ron Maupin
    Jun 21, 2016 at 17:57
  • sorry by arp entries I meant mac tables in switch.
    – user88975
    Jun 22, 2016 at 11:44
  • 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 can provide your own answer and accept it.
    – Ron Maupin
    Aug 6, 2017 at 20:10

1 Answer 1

  1. No, host A cannot get the IP of host B, as they are in different subnets, which typically also means they are in different Layer 2 domains, so they need a Router to communicate with each other.

  2. Just as with VLANs, you need a Router set up on the host as a default gateway to communicate with hosts in other VLANs/VXLANs.

You can read about how VTEPs do MAC learning in this article.

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