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From: Blue Swirl <blauwirbel@gmail.com>
Date: Wed, 15 Jun 2011 22:37:06 +0300
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Subject: Re: [Qemu-devel] user-mode networking not allowing internet traffic
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To: Amitava Shee <amitava.shee@gmail.com>
Cc: qemu-devel@nongnu.org

On Wed, Jun 15, 2011 at 9:12 PM, Amitava Shee <amitava.shee@gmail.com> wrot=
e:
> My ubuntu 11.04 guest is not able to connect to the internet when launche=
d
> as -net user. Any help is much appreciated.
>
> qemu command line
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> amitava@bonjovi:/var/vms$ qemu-system-x86_64 -m 512 -drive
> index=3D0,media=3Ddisk,if=3Dvirtio,file=3Dub2.qcow2,boot=3Don -vnc :0 -mo=
nitor stdio
> -net nic,model=3Dvirtio,vlan=3D1 -net user,vlan=3D1,hostname=3Dubuntu2
>
> ifconfig output in guest
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> amitava@ubuntu2:~$ ifconfig eth0
> eth0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Link encap:Ethernet=C2=A0 HWaddr 52:54=
:00:12:34:56
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 inet addr:10.0.2.1=
5=C2=A0 Bcast:10.0.2.255=C2=A0 Mask:255.255.255.0
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 inet6 addr: fe80::=
5054:ff:fe12:3456/64 Scope:Link
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 UP BROADCAST RUNNI=
NG MULTICAST=C2=A0 MTU:1500=C2=A0 Metric:1
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 RX packets:11 erro=
rs:0 dropped:0 overruns:0 frame:0
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 TX packets:16 erro=
rs:0 dropped:0 overruns:0 carrier:0
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 collisions:0 txque=
uelen:1000
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 RX bytes:1984 (1.9=
 KB)=C2=A0 TX bytes:1748 (1.7 KB)
>
> amitava@ubuntu2:~$ nslookup google
> Server:=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 10.0.2.3
> Address:=C2=A0=C2=A0=C2=A0 10.0.2.3#53
>
> Non-authoritative answer:
> Name:=C2=A0=C2=A0=C2=A0 google.com
> Address: 74.125.115.104
> Name:=C2=A0=C2=A0=C2=A0 google.com
> Address: 74.125.115.106
> Name:=C2=A0=C2=A0=C2=A0 google.com
> Address: 74.125.115.105
> Name:=C2=A0=C2=A0=C2=A0 google.com
> Address: 74.125.115.147
> Name:=C2=A0=C2=A0=C2=A0 google.com
> Address: 74.125.115.103
> Name:=C2=A0=C2=A0=C2=A0 google.com
> Address: 74.125.115.99

This and the IP address of the eth0 show that the connection is working.

> amitava@ubuntu2:~$ traceroute google.com
> traceroute to google.com (74.125.115.99), 30 hops max, 60 byte packets
> =C2=A01=C2=A0 10.0.2.2 (10.0.2.2)=C2=A0 0.469 ms=C2=A0 0.457 ms=C2=A0 0.4=
53 ms
> =C2=A02=C2=A0 * * *
> =C2=A03=C2=A0 * * *
> =C2=A04=C2=A0 * * *
> =C2=A05=C2=A0 * * *
> =C2=A06=C2=A0 * * *
> =C2=A07=C2=A0 * * *
> =C2=A08=C2=A0 * * *
> =C2=A09=C2=A0 * * *
> 10=C2=A0 * * *
> 11=C2=A0 * * *
> 12=C2=A0 * * *
> 13=C2=A0 * * *
> 14=C2=A0 * * *
> 15=C2=A0 * * *
> 16=C2=A0 * * *
> 17=C2=A0 * * *
> 18=C2=A0 * * *
> 19=C2=A0 * * *
> 20=C2=A0 * * *
> 21=C2=A0 * * *
> 22=C2=A0 * * *
> 23=C2=A0 * * *
> 24=C2=A0 * * *
> 25=C2=A0 * * *
> 26=C2=A0 * * *
> 27=C2=A0 * * *
> 28=C2=A0 * * *
> 29=C2=A0 * * *
> 30=C2=A0 * * *

User mode network (SLIRP) only supports plain TCP and UDP, traceroute
and ping (which need ICMP) do not work.