本文介绍怎样在kvm的虚拟环境下，部署实验LVS的DR模式。包含网络结构图，怎样配置。以及使用tcpdump分析ip包。
网络结构图
kvm节点（client）
192.168.7.2 （CIP）
|
br_e网桥
/ \
（VIP）
eth7：192.168.7.33 eth14: 192.168.7.99
lvs虚拟主机 server虚拟主机
（DIP） （RIP）
eth8：192.168.88.10 eth12: 192.168.88.20
\ /
br_lvs网桥
实验步骤
1.创建bridge：br_e和br_lvs，并分别设置ip
# kvm节点
$ ifconfig br_e 192.168.7.2 netmask 255.255.255.0
2.lvs配置
$ ipvsadm -A -t 192.168.7.33:8000 -s rr
$ ipvsadm -a -t 192.168.7.33:8000 -r 192.168.88.20 -g
3.server配置
# 让主机处理dst为192.168.7.33的ip包
# 子网掩码必须是255.255.255.255，假设是255.255.255.0则不会处理ip包
$ ifconfig lo:0 192.168.7.33 netmask 255.255.255.255 up
/etc/sysctl.conf配置（好像不须要设置？）
ip_forward=0 # 不须要配置为1
rp_filter = 0 # 默认配置
# 解决arp问题
# 官方文档说lo不须要设置arp
# 注销后没问题
# net.ipv4.conf.lo.arp_ignore = 0
# net.ipv4.conf.lo.arp_announce = 0
# eth14是br_e上的网卡
# 仅仅有当arp请求的目标ip和eth14上绑定ip同样时，eth14才会处理
# 否则lvs的vip会和server的vip冲突
# 在本例中，br_e网络中会存在两个192.168.7.33
net.ipv4.conf.eth14.arp_ignore = 1
# 用于eth14发送arp请求时src ip？
net.ipv4.conf.eth14.arp_announce = 2
# net.ipv4.conf.all.arp_ignore = 1
# net.ipv4.conf.all.arp_announce = 2
4.在server虚拟主机上开启web服务
# 默认监听8000port
$ python -m SimpleHTTPServer
5.在kvm节点（client）上
$ curl http://192.168.7.33:8000
tcpdump分析IP包
[kvm send: br_e] 发出ip包（syn）
00:1a:a0:21:21:65 > de:ad:be:ef:24:46, 192.168.7.2.51091 > 192.168.7.33.8000: Flags [S], seq 3773377896
[lvs recv: br_e]lvs收到ip包
00:1a:a0:21:21:65 > de:ad:be:ef:24:46, 192.168.7.2.51091 > 192.168.7.33.8000: Flags [S], seq 3773377896,
[lvs send: br_lvs] lvs改动ip包的mac，目标mac改成server的mac
00:16:3e:5d:a6:b3 > 52:54:00:ba:3d:b9, 192.168.7.2.51091 > 192.168.7.33.8000: Flags [S], seq 3773377896,
[server recv: br_lvs] server接收ip包（mac同样）
00:16:3e:5d:a6:b3 > 52:54:00:ba:3d:b9, 192.168.7.2.51091 > 192.168.7.33.8000: Flags [S], seq 3773377896
[server send: br_e] server发出ip包（ack） 。ip包的src是lvs的ip。 dst是client的ip
52:54:00:c1:a7:5e > 00:1a:a0:21:21:65, 192.168.7.33.8000 > 192.168.7.2.51091: Flags [S.], seq 3629588945, ack 3773377897
[kvm recv: br_e] client收到ip包（ack）
52:54:00:c1:a7:5e > 00:1a:a0:21:21:65, 192.168.7.33.8000 > 192.168.7.2.51091: Flags [S.], seq 3629588945, ack 3773377897
arp_ignore和arp_announce
arp_announce - INTEGER
Define different restriction levels for announcing the local
source IP address from IP packets in ARP requests sent on
interface:
0 - (default) Use any local address, configured on any interface
1 - Try to avoid local addresses that are not in the target‘s
subnet for this interface. This mode is useful when target
hosts reachable via this interface require the source IP
address in ARP requests to be part of their logical network
configured on the receiving interface. When we generate the
request we will check all our subnets that include the
target IP and will preserve the source address if it is from
such subnet. If there is no such subnet we select source
address according to the rules for level 2.
2 - Always use the best local address for this target.
In this mode we ignore the source address in the IP packet
and try to select local address that we prefer for talks with
the target host. Such local address is selected by looking
for primary IP addresses on all our subnets on the outgoing
interface that include the target IP address. If no suitable
local address is found we select the first local address
we have on the outgoing interface or on all other interfaces,
with the hope we will receive reply for our request and
even sometimes no matter the source IP address we announce.
The max value from conf/{all,interface}/arp_announce is used.
Increasing the restriction level gives more chance for
receiving answer from the resolved target while decreasing
the level announces more valid sender‘s information.
arp_ignore - INTEGER
Define different modes for sending replies in response to
received ARP requests that resolve local target IP addresses:
0 - (default): reply for any local target IP address, configured
on any interface
1 - reply only if the target IP address is local address
configured on the incoming interface
2 - reply only if the target IP address is local address
configured on the incoming interface and both with the
sender‘s IP address are part from same subnet on this interface
3 - do not reply for local addresses configured with scope host,
only resolutions for global and link addresses are replied
4-7 - reserved
8 - do not reply for all local addresses
The max value from conf/{all,interface}/arp_ignore is used
when ARP request is received on the {interface}
