[Openstack] instance cannot access external network (folsom quantum)

Gary Kotton gkotton at redhat.com
Thu Dec 13 12:38:24 UTC 2012

On 12/13/2012 12:07 PM, ZhiQiang Fan wrote:
> i can ping and ssh into instance with private ip and floating ip
> instance can ping the control node ip, but cannot ping the compute 
> node and any external network

In order to be able to help would it be possible that you provide IP 
addresses and maybe a bit of understanding about your topology.

Basically is there a route from the VM ip address to the IP address of 
the compute node?

In addition to this can you please let us know which plugin you are using?

> i have installed quantum in the control node host, and it only got 1 
> nic (same as compute node), and use eth0:0 and eth0:1 to vitualize 2 
> other nic (eth0:0 on compute node)
> i use tcpdump on control node and compute node to monitor package from 
> instance, actually compute node will reply the icmp package but with 
> destination of instance private ip, since compute node has no route to 
> that network, it failed and no package receive on control node nic. 
> but when i add route via control node, it can reply to insance as expected
> then i use tcpdump on control node and instance to monitor package to 
> the floating ip, instance got nothing but control node captured the 
> package and reply it instead of instance
> so i think the problem may be that the control node will not modify 
> the source ip when forwad the icmp package, more exactly, the nat 
> functionality is not enabled?
> and i try some other command such as "iptables -t nat -A POSTROUTING 
> -o eth0 -j MASQUERADE" but it is not working
> i'll paste some output if anyone needs
> thanks
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