NAT interface on Proxmox VE3.0 does NOT work!

[Masateru KUWATA]

Dear Sir,

I have created several VMs on proxmox VE3.0 (2 for Windows, 3 for Linux). At the first time, I configured all virtual network as NAT mode.

It has been running without a problem for about two weeks. Then I noticed that this NAT definition is problematic. A Guest OS was given an dhcp address by KVM (e.g. 10.0.2.10) where the default gateway was 10.0.2.2 and DNS server was 10.0.2.3. A guest OS can access to 10.0.2.2 and 10.0.2.3, but it could not access to outisde NAT. I am not sure when this problem occured (because every VMs were working after initial setup).

However once happened, there is no way to recover -- even after rebooting KVM kernel, a Guest OS cannot go out of NAT.


Then I modified all virtual network cards of VM to the bridge definition. The problem was eliminated and everything works fine.

How can I diagnose this problem in more detail? I can reproduce this problem by using NAT mode, but don't know how to debug.

Any suggestions and advices are appreciated.
best regards

 

[udo]

Hi,
you can try to use "tcpdump" to find the issue.

Udo

 

[Masateru KUWATA]

Thank you sir,

I tried to trace by using "tcpdump -i eth0". However, what I got is a trace of ICMP echo request from guest OS, and of course no ICMP echo reply (when using NAT mode".

Can you please tell me how to get more detailed information about the inside of NAT?


Regards

 

[spirit]

Dear Sir,

I have created several VMs on proxmox VE3.0 (2 for Windows, 3 for Linux). At the first time, I configured all virtual network as NAT mode.

It has been running without a problem for about two weeks. Then I noticed that this NAT definition is problematic. A Guest OS was given an dhcp address by KVM (e.g. 10.0.2.10) where the default gateway was 10.0.2.2 and DNS server was 10.0.2.3. A guest OS can access to 10.0.2.2 and 10.0.2.3, but it could not access to outisde NAT. I am not sure when this problem occured (because every VMs were working after initial setup).

However once happened, there is no way to recover -- even after rebooting KVM kernel, a Guest OS cannot go out of NAT.


Then I modified all virtual network cards of VM to the bridge definition. The problem was eliminated and everything works fine.

How can I diagnose this problem in more detail? I can reproduce this problem by using NAT mode, but don't know how to debug.

Any suggestions and advices are appreciated.
best regards

current kvm nat mode (in proxmox) use userland qemu network with integrated dhcp inside qemu
http://wiki.qemu.org/Documentation/Networking#User_Networking_.28SLIRP.29
performance is lower than bridge.
you need to an iptables postrouting rules to do the nat
http://pve.proxmox.com/wiki/Network_Model#Masquerading_.28NAT.29



I think the plan for next proxmox releases is to migrate to a bridge with nat (without eth0 plugged, using the bridge ip as gateway + nat).
And that need to add guest ip management in proxmox + dhcp, etc...

 

[Masateru KUWATA]

Dear Sir,

Thanks for your notice.

Maybe it is better for me to wait until the next release for NAT support.

Thanks and Regards

current kvm nat mode (in proxmox) use userland qemu network with integrated dhcp inside qemu
http://wiki.qemu.org/Documentation/Networking#User_Networking_.28SLIRP.29
performance is lower than bridge.
you need to an iptables postrouting rules to do the nat
http://pve.proxmox.com/wiki/Network_Model#Masquerading_.28NAT.29



I think the plan for next proxmox releases is to migrate to a bridge with nat (without eth0 plugged, using the bridge ip as gateway + nat).
And that need to add guest ip management in proxmox + dhcp, etc...