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From: Thomas Huth <thuth@redhat.com>
Message-ID: <572093EB.8030502@redhat.com>
Date: Wed, 27 Apr 2016 12:26:51 +0200
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Subject: Re: [Qemu-devel] Is anyone able to load a web page from a guest
 operating system?
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To: Laszlo Ersek <lersek@redhat.com>, Programmingkid <programmingkidx@gmail.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>, qemu-devel qemu-devel <qemu-devel@nongnu.org>

On 27.04.2016 12:05, Laszlo Ersek wrote:
> On 04/26/16 22:12, Thomas Huth wrote:
>> On 26.04.2016 21:25, Programmingkid wrote:
>>> On Apr 26, 2016, at 3:00 PM, Dr. David Alan Gilbert wrote:
> 
>>>> Does ping work?
>>> I can ping the virtual router at 10.0.2.2. Any other ip address fails. 
>>
>> That's normal for user-mode / slirp networking. You can't ping external
>> hosts with this mode.
> 
> Side note: yes, you can.
> 
> I do it whenever I want to check network connectivity from within ad-hoc
> OVMF guests, using the PING command of the UEFI shell. ("Ad-hoc guest"
> implies user-mode / slirp.)
> 
> It can be enabled with the following steps:
> 
> (1) Determine the main group ID (or one supplementary group ID) of the
> user that will run QEMU with slirp.
> 
> (2) In /etc/sysctl.conf (or whatever is appropriate for your host
> distro), make sure that the whitespace separated inclusive group ID
> range in the "net.ipv4.ping_group_range" sysctl includes the above group ID.

Wow, thanks for that hint, I just tried by temporarily enabling it with

 sudo sysctl net.ipv4.ping_group_range=...

and indeed it works!

Maybe we should document that somewhere?
For example  http://qemu-project.org/Documentation/Networking currently
only says: "ICMP traffic does not work (so you cannot use ping within a
guest)" ...

 Thomas