kvm初体验之五：vm连接网络的两种方式：bridge和nat1. 在安装vm时指定网络连接方式
1）bridge
virt-install --name vm1 --ram=1024 --vcpus=1 --disk path=/vm-images/vm1,size=2 --cdrom /root/iso/CentOS-6.6-x86_64-minimal.iso --network bridge:br0
2）nat
virt-install --name vm1 --ram=1024 --vcpus=1 --disk path=/vm-images/vm1,size=2 --cdrom /root/iso/CentOS-6.6-x86_64-minimal.iso --network network:default
若没有指定—network参数，默认为bridge方式
2. 在安装vm之后修改网络连接方式
修改vm网络连接方式之前先将vm关机，修改完成之后启动vm即可生效。
1）通过图形界面修改
用virt-manager打开vm的管理页面，如下图所示
nat：选择”Sourcedevice”为Virtualnetwork 'default': NAT
bridge: 选择”Sourcedevice”为Hostdevice eth0 (Bridge 'br0')
2）通过命令行修改
virsh edit vm1修改vm1的配置文件（vm的配置文件以xml形式存在，如vm1.xml）
<interface>选项用来指定vm的网络连接方式
nat:
<interface type='network'>
<mac address='52:54:00:eb:d7:7d'/>
<source network='default'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
bridge:
<interface type='bridge'>
<mac address='52:54:00:eb:d7:7d'/>
<source bridge='br0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
3. 新增virtual network
1）通过图形界面添加
virt-manager打开vm管理界面，选择Edit->Connection Details，在弹出的localhost Connection Details窗口的Virtual Networks选项卡中显示了当前已经存在virtual network。在host中安装了libvirt之后，会默认创建虚拟网络接口virbr0，它的forwarding方式为nat。
现在我们创建一个虚拟网络nat1，forwarding方式为nat
选择上图左框中的“+”
Forward
Forwad
Forwad
Forwad
Forwad
Finish.
Localhost Connection Details窗口中显示出了新增的nat1网络的信息。
将vm1的虚拟网络接口选为刚刚创建的nat1
将vm1先关机后启动
由下图可以看到，vm1获取到了nat1网络所配地址段中的地址。
2）通过命令行添加
参考：http://wiki.libvirt.org/page/Networking
virsh下的net-xxx命令用来管理虚拟网络
[root@tanghuimin thm]# virsh
Welcome to virsh, the virtualization interactive terminal.
Type: 'help' for help with commands
'quit' to quit
virsh # net-
net-autostart net-define net-dumpxml net-info net-name net-undefine net-uuid
net-create net-destroy net-edit net-list net-start net-update
net-list –all列出当前已经存在的virtualnetwork
virsh # net-list --all
Name State Autostart Persistent
--------------------------------------------------
default active yes yes
nat1 active yes yes
virtual network的配置文件同样是以xml的形式存在，如nat1.xml
[root@tanghuimin thm]# find / -name "nat1.xml"
/etc/libvirt/qemu/networks/nat1.xml
/etc/libvirt/qemu/networks/autostart/nat1.xml
/var/lib/libvirt/network/nat1.xml
以default网络的配置为模板创建虚拟网络nat2的配置文件
[root@tanghuimin thm]# virsh net-dumpxml default >/etc/libvirt/qemu/networks/nat2.xml
修改nat2.xml中参数使与已存在的虚拟网络不重合。
<network>
<name>nat2</name>
<uuid>d8d274ff-fe1f-4e88-94f9-222c1ae11c69</uuid>
<forward mode='nat'/>
<bridge name='virbr2' stp='on' delay='0' />
<mac address='52:54:00:25:90:C2'/>
<ip address='192.168.101.1' netmask='255.255.255.0'>
<dhcp>
<range start='192.168.101.2' end='192.168.101.254' />
</dhcp>
</ip>
</network>
net-define从xml文件定义虚拟网络
virsh # net-list --all
Name State Autostart Persistent
--------------------------------------------------
default active yes yes
nat1 active yes yes
virsh # net-define /etc/libvirt/qemu/networks/nat2.xml
Network nat2 defined from /etc/libvirt/qemu/networks/nat2.xml
virsh # net-list --all
Name State Autostart Persistent
--------------------------------------------------
default active yes yes
nat1 active yes yes
nat2 inactive no yes
将nat2设为自启动，并启动nat2
virsh # net-autostart nat2
Network nat2 marked as autostarted
virsh # net-start nat2
Network nat2 started
virsh # net-list --all
Name State Autostart Persistent
--------------------------------------------------
default active yes yes
nat1 active yes yes
nat2 active yes yes
将vm1的虚拟网络接口选为刚刚创建的nat2
virsh edit vm1
......
......
<interface type='network'>
<mac address='52:54:00:eb:d7:7d'/>
<source network='nat2'/>
<address type='pci' domain='0x0000' bus='0x00'slot='0x03' function='0x0'/>
</interface>
......
......
将vm1先关机后启动
由下图可以看到，vm1获取到了nat2网络所配地址段中的地址。
[root@localhost ~]# ifconfig
eth0 Link encap:Ethernet HWaddr 52:54:00:EB:D7:7D
inet addr:192.168.101.21 Bcast:192.168.101.255 Mask:255.255.255.0
inet6 addr: fe80::5054:ff:feeb:d77d/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:12 errors:0 dropped:0 overruns:0 frame:0
TX packets:16 errors:0 dropped:0 overruns:0carrier:0
collisions:0 txqueuelen:1000
RX bytes:1198 (1.1 KiB) TX bytes:2178 (2.1 KiB)
Interrupt:11 Base address:0x8000
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:65536 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:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
[root@localhost ~]# ping 192.168.1.1
PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
64 bytes from 192.168.1.1: icmp_seq=1 ttl=63 time=5.53 ms
#
--- 192.168.1.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 926ms
rtt min/avg/max/mdev = 5.531/5.531/5.531/0.000 ms
