VM Interconnectivity

 Scenario

VM1 can not send TCP traffic to VM2.

We want to determine how far the packet is reaching before being lost.

 Determine physical compute hosts

To find out on which physical compute hosts these VMs live on, log into Horizon as administrative user and navigate to the instances page.

Find the VMs in the list and note the down the compute hosts, Internal IPs and Floating IPs:

VM1: compute1, 192.168.0.1, 172.16.0.1

VM2: compute2, 192.168.0.2, 172.16.0.2

 Determine TAP interfaces

TAP interface names consists of the string "tap", followed by the first 11 characters of the VM’s port UUID.

To determine the VM’s port UUID, navigate to the VM’s network in Horizon and search the port list for the VM’s internal IP. Construct the TAP interface name from it like in the following example:

Port UUID: 7aa08012-d06c-4c78-aee8-1fff7c063fed

TAP interface: tap7aa08012-d0

 Examine the traffic on the TAP interfaces

In order to verify if the traffic is being seen on a VM’s virtual NIC without logging into the guest host, you can use tcpdump on the VM’s TAP interface on the compute host.

# tcpdump -n -i tap7aa08012-d0

Watch packet counters on the TAP interface:

# watch -d ip -s link show tap7aa08012-d0
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