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Packet flow in linux-bridge environment

I wanted to understand the packet flow in neutron. The scenario is particularly the case where an instance receives an IP address from the DHCP process running on the controller node.

One of my instances was not getting an IP address to its eth0 interface. Upon debugging, i found out in '/var/log/messages' that it didnot receive a DHCP Offer.

So i started capturing bootp packets on all the interfaces.

1) Ran dhclient on the VM. 2) Captured Bootp packets on the tap interface on compute node 3) Captured Bootp packets on the brq interface on compute node. [linux bridge -newton install openstack] 4) captured bootp packets on vxlan-85 interface on compute node.

All these dumps had the packets. Then i figured out the physical interface on the compute node that establishes the tunnel network. I checked the "/etc/neutron/plugins/ml2/linuxbridgeagent.ini" file and in the [vxlan] section, checked for the physical interface whose IP was listed in the [vxlan] section.

When i tried a tcpdump on this physical interface , i saw no packets.

So i wanted to understand what is the packet flow route? Why should i not expect these bootp packets on the physical interfaces on the compute and the controller machines which are configured in the [vxlan] section in the "/etc/neutron/plugins/ml2/linuxbridgeagent.ini" file?