While brought up your guest OS, If you didn't specify any nic interface, by default QEMU will create one and assign the IP 10.0.2.15. but it will not have any connectivity. so guest OS will not able to ping host OS.
(For more details about QEMU networking refer http://wiki.qemu.org/Documentation/Networking).
Better way I would suggest is bridge->tap configuration. All you have to do is:
- Install ethernet bridge administration(brctl) ->
sudo apt-get install bridge-utils
- Install tunctl to create and manage persistent TUN/TAP interfaces ->
sudo apt-get install uml-utilities
- Install libvirt-visualization management system. This will automatically setup a DHCP server and a bridge(virbr0) ->
sudo apt-get install qemu-kvm libvirt-bin
Verify whether DHCP server is runing:
root@unknown:~# ps -ef | grep dns
121 1377 1 0 Dec13 ? 00:00:00 /usr/sbin/dnsmasq -u libvirt-dnsmasq --strict-order --bind-interfaces --pid-file=/var/run/libvirt/network/default.pid --conf-file= --except-interface lo --listen-address 192.168.122.1 --dhcp-range 192.168.122.2,192.168.122.254 --dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases --dhcp-lease-max=253 --dhcp-no-override
Verify bridge interface is created, and it is configured to DHCP gateway:
root@unknown:~# ifconfig virbr0
virbr0 Link encap:Ethernet HWaddr 62:80:41:0f:0b:56
inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:619 errors:0 dropped:0 overruns:0 frame:0
TX packets:685 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:44276 (44.2 KB) TX bytes:51576 (51.5 KB)
4. Bind eth0 to virbr0 -> brctl addif virbr0 eth0
5.Create a tap interface and make it up -> tunctl -t tap0 && ifconfig tap0 up
6.Bind tap0 to virbr0 -> brctl addif virbr0 tap0
7.Make sure tap0ð0 are binded:
root@unknown:~# brctl show
bridge name bridge id STP enabled interfaces
virbr0 8000.1a9819c54ba8 yes eth0
tap0
8.My configuration:
root@unknown:~# ifconfig
eth0 Link encap:Ethernet HWaddr 48:84:3c:c6:33:34
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:20070 errors:0 dropped:0 overruns:0 frame:0
TX packets:20070 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1697375 (1.6 MB) TX bytes:1697375 (1.6 MB)
tap0 Link encap:Ethernet HWaddr 1a:98:19:c5:4b:a8
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:500
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
virbr0 Link encap:Ethernet HWaddr 78:84:3c:e6:38:98
inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:619 errors:0 dropped:0 overruns:0 frame:0
TX packets:685 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:44276 (44.2 KB) TX bytes:51576 (51.5 KB)
wlan0 Link encap:Ethernet HWaddr cd:af:76:c4:6d:99
inet addr:192.168.1.5 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: ff70::ceff:78dd:fdc1:6d95/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1338984 errors:0 dropped:0 overruns:0 frame:0
TX packets:997145 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1521507128 (1.5 GB) TX bytes:142971835 (142.9 MB)
9. Brought qemu with NIC -
qemu-system-arm -kernel kernel-qemu -cpu arm1176 -m 256 -M versatilepb -no-reboot -serial stdio -append "root=/dev/sda2 panic=1 rootfstype=ext4 rw" -hda 2014-09-09-wheezy-raspbian.img -net nic,macaddr=00:16:3e:00:00:01 -net tap,ifname=tap0,script=no,downscript=no

Refer this