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I wanted to know why I am not able to ping from a physical machine's network interface (a private network) to another physical machine (this one has two network interfaces: a private interface that pings great to the first machine's private address and an external interface set up to access the internet.

I am running Ubuntu 14.04 LTS on both machines and I am trying to follow Openstack's image below:

Diagram

I have set static addresses to all three interfaces on the machines.

I hope I am clear enough on this question. Any help or guidance would be greatly appreciated! :)

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    Is there a network path from the internal interface to the external one? I'm assuming not, since its internal, unless your compute1 node is acting as a router.
    – heavyd
    Apr 30, 2014 at 17:37
  • Could you please post the routing table of 10.0.0.31? Most likely, the rub is there.
    – MariusMatutiae
    Apr 30, 2014 at 18:22

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To provide connectivity between two separate IP subnets, you need something to act as an IP router (or a higher-level gateway, such as a NAT gateway) connecting those subnets. If you don't already have an IP router or NAT gateway connecting the two subnets, you could use one of your existing boxes that is connected to both subnets. Since your compute node compute1 is connected to both subnets, you could allow it to be the router by enabling "IP forwarding" on it.

To enable it on the fly (doesn't persist across reboots): 

sudo sysctl -w net.ipv4.ip_forward=1

To enable it at boot, edit /etc/sysctl.conf and add this line:

net.ipv4.ip_forward = 1

Then, you would need to make sure your other machines on the 10.0.0.0/24 management subnet are configured to use the 10.0.0.x address of compute1 (10.0.0.31 in your diagram) as their default router/gateway.

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