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没有使用DVR的场景：
从图中可以明显看到东西向和南北向的流量会集中到网络节点，这会使网络节点成为瓶颈。
如果启用DVR，如下图：
对于东西向的流量， 流量会直接在计算节点之间传递。
VM1 (10.0.1.5 Net1) ping VM2 (10.0.2.5 Net2)
1) VM1 (10.0.1.5) -> qr (10.0.1.1)
VM1 根据默认路由发送arp（广播）请求qr网关的地址，请求到网关地址后，icmp报文走向qr口。
（关于报文格式的一点解释，当VM1 ping VM2时，报文的源/目的IP始终不变，报文的源/目的MAC则会根据不同的路段而变化。）
同时，br-tun网桥会丢弃目的地址是interface_distributed接口的arp广播，不至于让不必要的流量流向外面：
# ovs-ofctl dump-flows br-tun NXST_FLOW reply (xid=0x4): ... cookie=0x0, duration=64720.432s, table=1, n_packets=4, n_bytes=168, idle_age=64607, priority=3,arp,dl_vlan=1,arp_tpa=10.0.1.1 actions=drop ...
2）qr (10.0.1.1) -> qr (10.0.2.1)
进入qrouter namespace后，利用linux内核的高级路由功能，查看路由规则。
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa ip rule 0: from all lookup local 32766: from all lookup main 32767: from all lookup default 32768: from 10.0.1.5 lookup 16 32769: from 10.0.2.3 lookup 16 167772417: from 10.0.1.1/24 lookup 167772417 167772417: from 10.0.1.1/24 lookup 167772417 167772673: from 10.0.2.1/24 lookup 167772673
先查看main表：
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa ip route list table main 10.0.1.0/24 dev qr-ddbdc784-d7 proto kernel scope link src 10.0.1.1 10.0.2.0/24 dev qr-001d0ed9-01 proto kernel scope link src 10.0.2.1 169.254.31.28/31 dev rfp-0fbb351e-a proto kernel scope link src 169.254.31.28
在main表中满足以上路由，因此会从另一个qr口出去。（Q1：不同计算节点的同一子网下qr口ip是相同的吗？）
3）qr -> br-int
之后需要去查询10.0.2.5的MAC地址， MAC是由neutron使用静态ARP的方式设定的，由于Neutron知道所有VM的信息，因此他可以事先设定好静态ARP：
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa ip nei 10.0.1.5 dev qr-ddbdc784-d7 lladdr fa:16:3e:da:75:6d PERMANENT 10.0.2.3 dev qr-001d0ed9-01 lladdr fa:16:3e:a4:fc:98 PERMANENT 10.0.1.6 dev qr-ddbdc784-d7 lladdr fa:16:3e:9f:55:67 PERMANENT 10.0.2.2 dev qr-001d0ed9-01 lladdr fa:16:3e:13:55:66 PERMANENT 10.0.2.5 dev qr-001d0ed9-01 lladdr fa:16:3e:51:99:b8 PERMANENT 10.0.1.4 dev qr-ddbdc784-d7 lladdr fa:16:3e:da:e3:6e PERMANENT 10.0.1.7 dev qr-ddbdc784-d7 lladdr fa:16:3e:14:b8:ec PERMANENT 169.254.31.29 dev rfp-0fbb351e-a lladdr 42:0d:9f:49:63:c6 STALE
此时，报文进入br-int，根据table 0 进行normal转发：
cookie=0x0, duration=16440.644s, table=0, n_packets=1074, n_bytes=104318, idle_age=8917, priority=1 actions=NORMAL
normal动作则表示根据OVS fdb表项匹配目的MAC地址，从而决定该报文要往哪个端口发送。如果没有该MAC的fdb表项记录，则进行泛洪，对除了报文进来的端口以外的所有同属于一个vlan的端口发送该报文。例如：
# ovs-appctl fdb/show br-int port VLAN MAC Age LOCAL 0 da:91:42:cd:fb:44 18 18 0 52:54:00:a9:b8:b0 0 19 0 52:54:00:a9:b8:b1 0
因此如果此时VM2也在该compute node上，则VM2也会直接收到该报文，不需要走br-tun（有了VM2的MAC fdb表项记录后）。否则，继续往br-tun走。
4）br-int -> br-tun -> 出compute node 1
然后报文从br-int进入br-tun匹配流表：
cookie=0x0, duration=66172.51s, table=0, n_packets=58, n_bytes=5731, idle_age=20810, hard_age=65534, priority=1,in_port=3 actions=resubmit(,4) cookie=0x0, duration=67599.526s, table=0, n_packets=273, n_bytes=24999, idle_age=1741, hard_age=65534, priority=1,in_port=1 actions=resubmit(,1) cookie=0x0, duration=64437.052s, table=0, n_packets=28, n_bytes=2980, idle_age=20799, priority=1,in_port=4 actions=resubmit(,4) cookie=0x0, duration=67601.704s, table=0, n_packets=5, n_bytes=390, idle_age=65534, hard_age=65534, priority=0 actions=drop cookie=0x0, duration=66135.811s, table=1, n_packets=140, n_bytes=13720, idle_age=65534, hard_age=65534, priority=1,dl_vlan=1,dl_src=fa:16:3e:66:13:af actions=mod_dl_src:fa:16:3f:fe:49:e9,resubmit(,2) cookie=0x0, duration=64082.141s, table=1, n_packets=2, n_bytes=200, idle_age=64081, priority=1,dl_vlan=2,dl_src=fa:16:3e:69:b4:05 actions=mod_dl_src:fa:16:3f:fe:49:e9,resubmit(,2) cookie=0x0, duration=66135.962s, table=1, n_packets=1, n_bytes=98, idle_age=65301, hard_age=65534, priority=2,dl_vlan=1,dl_dst=fa:16:3e:66:13:af actions=drop cookie=0x0, duration=64082.297s, table=1, n_packets=0, n_bytes=0, idle_age=64082, priority=2,dl_vlan=2,dl_dst=fa:16:3e:69:b4:05 actions=drop cookie=0x0, duration=66136.115s, table=1, n_packets=4, n_bytes=168, idle_age=65534, hard_age=65534, priority=3,arp,dl_vlan=1,arp_tpa=10.0.1.1 actions=drop cookie=0x0, duration=64082.449s, table=1, n_packets=2, n_bytes=84, idle_age=63991, priority=3,arp,dl_vlan=2,arp_tpa=10.0.2.1 actions=drop cookie=0x0, duration=67599.22s, table=1, n_packets=123, n_bytes=10687, idle_age=1741, hard_age=65534, priority=0 actions=resubmit(,2)
先匹配table 0，然后匹配table 1，它会把源MAC地址（另一个qr口）改为全局唯一与计算节点绑定的MAC。
同时，后面的两条table1会丢弃目标ip是interface_distributed接口的ARP和目的MAC是interface_distributed的包，以防止虚机发送给本地IP的包不会被转发到网络中。
然后继续查询table 2，table 2是vxlan表，如果是广播包就会查询表22，如果是单播包就查询table 20
cookie=0x0, duration=67601.554s, table=2, n_packets=176, n_bytes=16981, idle_age=20810, hard_age=65534, priority=0,dl_dst=00:00:00:00:00:00/01:00:00:00:00:00 actions=resubmit(,20) cookie=0x0, duration=67601.406s, table=2, n_packets=92, n_bytes=7876, idle_age=1741, hard_age=65534, priority=0,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00 actions=resubmit(,22)
广播MAC地址是FF:FF:FF:FF:FF:FF，组播MAC地址以01-00-5E开头（具体可查看http://book.51cto.com/art/200904/120471.htm），匹配规则满足CIDR。
ICMP包是单播包，因此会查询表20，由于开启了L2 pop功能，在表20中会事先学习到应该转发到哪个VTEP：
cookie=0x0, duration=64015.308s, table=20, n_packets=0, n_bytes=0, idle_age=64015, priority=2,dl_vlan=2,dl_dst=fa:16:3e:51:99:b8 actions=strip_vlan,set_tunnel:0x3eb,output:4
(Q2：社区br-tun下面的隧道口是如何与物理口建立联系的?)
5）进compute node 2 -> br-tun
在br-tun中，从外面进入的报文将首先匹配以下table0表：
cookie=0x0, duration=66293.658s, table=0, n_packets=31, n_bytes=3936, idle_age=22651, hard_age=65534, priority=1,in_port=3 actions=resubmit(,4) cookie=0x0, duration=69453.368s, table=0, n_packets=103, n_bytes=9360, idle_age=22651, hard_age=65534, priority=1,in_port=1 actions=resubmit(,1) cookie=0x0, duration=66292.808s, table=0, n_packets=20, n_bytes=1742, idle_age=3598, hard_age=65534, priority=1,in_port=4 actions=resubmit(,4) cookie=0x0, duration=69455.675s, table=0, n_packets=5, n_bytes=390, idle_age=65534, hard_age=65534, priority=0 actions=drop
在table 4中，会将对应的vni改为本地vlan id，之后查询表9:
cookie=0x0, duration=65937.871s, table=4, n_packets=32, n_bytes=3653, idle_age=22651, hard_age=65534, priority=1,tun_id=0x3eb actions=mod_vlan_vid:3,resubmit(,9) cookie=0x0, duration=66294.732s, table=4, n_packets=19, n_bytes=2025, idle_age=3598, hard_age=65534, priority=1,tun_id=0x3e9 actions=mod_vlan_vid:2,resubmit(,9) cookie=0x0, duration=69455.115s, table=4, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=0 actions=drop
在表9中，如果发现包的源地址是全局唯一并与计算节点绑定的MAC地址，就将其转发到br-int:
cookie=0x0, duration=69453.507s, table=9, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=1,dl_src=fa:16:3f:fe:49:e9 actions=output:1 cookie=0x0, duration=69453.782s, table=9, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=1,dl_src=fa:16:3f:72:3f:a7 actions=output:1 cookie=0x0, duration=69453.23s, table=9, n_packets=56, n_bytes=6028, idle_age=3598, hard_age=65534, priority=0 actions=resubmit(,10)
6）br-tun -> br-int
进入br-int后，在table 0中，如果是全局唯一并与计算节点绑定的MAC地址就查询table 1，否则就正常转发；
在table 1中，事先设定好了flow，如果目的MAC是发送给VM2，就将源MAC改为Net2的网关MAC地址（qr口）（Q3：修改源MAC的原因）。
cookie=0x0, duration=70039.903s, table=0, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=2,in_port=6,dl_src=fa:16:3f:72:3f:a7 actions=resubmit(,1) cookie=0x0, duration=70039.627s, table=0, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=2,in_port=6,dl_src=fa:16:3f:fe:49:e9 actions=resubmit(,1) cookie=0x0, duration=70040.053s, table=0, n_packets=166, n_bytes=15954, idle_age=4184, hard_age=65534, priority=1 actions=NORMAL cookie=0x0, duration=66458.695s, table=1, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=4,dl_vlan=3,dl_dst=fa:16:3e:51:99:b8 actions=strip_vlan,mod_dl_src:fa:16:3e:69:b4:05,output:12 cookie=0x0, duration=66877.515s, table=1, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=4,dl_vlan=2,dl_dst=fa:16:3e:14:b8:ec actions=strip_vlan,mod_dl_src:fa:16:3e:66:13:af,output:9 cookie=0x0, duration=66877.369s, table=1, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=2,ip,dl_vlan=2,nw_dst=10.0.1.0/24 actions=strip_vlan,mod_dl_src:fa:16:3e:66:13:af,output:9 cookie=0x0, duration=66458.559s, table=1, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=2,ip,dl_vlan=3,nw_dst=10.0.2.0/24 actions=strip_vlan,mod_dl_src:fa:16:3e:69:b4:05,output:12
7）br-int -> VM2
至此，VM2就会收到VM1的包了。从通信的过程可以看到，跨网段的东西向流量没有经过网络节点。
VM1 （local ip：10.0.1.5 , floating ip: 172.24.4.5）ping 8.8.8.8
1）VM1 (10.0.1.5) -> qr (10.0.1.1)
与上面一致
2) qr (10.0.1.1) -> rfp (169.254.31.28) -> fpr (169.254.31.29)
进入qrouter namespace后：
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa ip rule 0: from all lookup local 32766: from all lookup main 32767: from all lookup default 32768: from 10.0.1.5 lookup 16 32769: from 10.0.2.3 lookup 16 167772417: from 10.0.1.1/24 lookup 167772417 167772417: from 10.0.1.1/24 lookup 167772417 167772673: from 10.0.2.1/24 lookup 167772673
在main表中没有合适的路由：
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa ip route list table main 10.0.1.0/24 dev qr-ddbdc784-d7 proto kernel scope link src 10.0.1.1 10.0.2.0/24 dev qr-001d0ed9-01 proto kernel scope link src 10.0.2.1 169.254.31.28/31 dev rfp-0fbb351e-a proto kernel scope link src 169.254.31.28
由于包是从10.0.1.5发来的之后会查看table 16，包会命中这条路由。
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa ip route list table 16 default via 169.254.31.29 dev rfp-0fbb351e-a
路由之后会通过netfilter的POSTROUTING链中进行SNAT：
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa iptables -nvL -t nat ... Chain neutron-l3-agent-float-snat (1 references) pkts bytes target prot opt in out source destination 0 0 SNAT all -- * * 10.0.2.3 0.0.0.0/0 to:172.24.4.7 0 0 SNAT all -- * * 10.0.1.5 0.0.0.0/0 to:172.24.4.5 ...
之后就可以看到包会通过rfp-0fbb351e-a发送给169.254.31.29。
端口rfp-0fbb351e-a和fpr-0fbb351e-a是一对veth pair。在fip namespace中你可以看到这个接口：
3) fpr (169.254.31.29) -> fg (172.24.4.6)
到了fip的namespace之后，会查询路由， 在main表里有通往公网的默认路由：
# ip netns exec fip-fbd46644-c70f-4227-a414-862a00cbd1d2 ip route default via 172.24.4.1 dev fg-081d537b-06 169.254.31.28/31 dev fpr-0fbb351e-a proto kernel scope link src 169.254.31.29 172.24.4.0/24 dev fg-081d537b-06 proto kernel scope link src 172.24.4.6 172.24.4.5 via 169.254.31.28 dev fpr-0fbb351e-a 172.24.4.7 via 169.254.31.28 dev fpr-0fbb351e-a
通过fg-081d537b-06发送到br-ex。这是从虚机发送到公网的过程。(Q4：br-ex上的流表是什么样的？如果没有br-ex，直接走br-int，流表会有什么变化？)
外网 ping VM1 ( floating ip: 172.24.4.5)
1）fip namespace
此时fip的namespace会做arp代理：（Q5：arp代理的作用？）
# ip netns exec fip-fbd46644-c70f-4227-a414-862a00cbd1d2 sysctl net.ipv4.conf.fg-081d537b-06.proxy_arp net.ipv4.conf.fg-081d537b-06.proxy_arp = 1
可以看到接口的arp代理是打开的，对于floating ip 有以下路由：
# ip netns exec fip-fbd46644-c70f-4227-a414-862a00cbd1d2 ip route ... 172.24.4.5 via 169.254.31.28 dev fpr-0fbb351e-a 172.24.4.7 via 169.254.31.28 dev fpr-0fbb351e-a ...
ARP会去通过VETH Pair到IR(Inter Router)的namespace中去查询，在IR中可以看到，接口rfp-0fbb351e-a配置了floating ip:
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa ip addr 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: rfp-0fbb351e-a: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 link/ether ea:5c:56:9a:36:9c brd ff:ff:ff:ff:ff:ff inet 169.254.31.28/31 scope global rfp-0fbb351e-a valid_lft forever preferred_lft forever inet 172.24.4.5/32 brd 172.24.4.5 scope global rfp-0fbb351e-a valid_lft forever preferred_lft forever inet 172.24.4.7/32 brd 172.24.4.7 scope global rfp-0fbb351e-a valid_lft forever preferred_lft forever inet6 fe80::e85c:56ff:fe9a:369c/64 scope link valid_lft forever preferred_lft forever 17: qr-ddbdc784-d7: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default link/ether fa:16:3e:66:13:af brd ff:ff:ff:ff:ff:ff inet 10.0.1.1/24 brd 10.0.1.255 scope global qr-ddbdc784-d7 valid_lft forever preferred_lft forever inet6 fe80::f816:3eff:fe66:13af/64 scope link valid_lft forever preferred_lft forever 19: qr-001d0ed9-01: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default link/ether fa:16:3e:69:b4:05 brd ff:ff:ff:ff:ff:ff inet 10.0.2.1/24 brd 10.0.2.255 scope global qr-001d0ed9-01 valid_lft forever preferred_lft forever inet6 fe80::f816:3eff:fe69:b405/64 scope link valid_lft forever preferred_lft forever
因此fip的namespace会对这个floating ip进行ARP回应。
外部发起目标地址为floating ip的请求后，fip会将其转发到IR中，IR的RPOROUTING链中规则如下：
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa iptables -nvL -t nat ... Chain neutron-l3-agent-PREROUTING (1 references) pkts bytes target prot opt in out source destination 0 0 REDIRECT tcp -- * * 0.0.0.0/0 169.254.169.254 tcp dpt:80 redir ports 9697 0 0 DNAT all -- * * 0.0.0.0/0 172.24.4.7 to:10.0.2.3 0 0 DNAT all -- * * 0.0.0.0/0 172.24.4.5 to:10.0.1.5 ...
这条DNAT规则会将floating ip地址转换为内部地址，之后进行路由查询：
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa ip route 10.0.1.0/24 dev qr-ddbdc784-d7 proto kernel scope link src 10.0.1.1 10.0.2.0/24 dev qr-001d0ed9-01 proto kernel scope link src 10.0.2.1 169.254.31.28/31 dev rfp-0fbb351e-a proto kernel scope link src 169.254.31.28
目的地址是10.0.1.0/24网段的，因此会从qr-ddbdc784-d7转发出去。之后就会转发到br-int再到虚机。
在虚机没有floating ip的情况下，从虚机发出的包会首先到IR，IR中查询路由：
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa ip rule 0: from all lookup local 32766: from all lookup main 32767: from all lookup default 32768: from 10.0.1.5 lookup 16 32769: from 10.0.2.3 lookup 16 167772417: from 10.0.1.1/24 lookup 167772417 167772673: from 10.0.2.1/24 lookup 167772673
会先查询main表，之后查询167772417表。（Q7：不会匹配table 16？）
# ip netns exec qrouter-0fbb351e-a65b-4790-a409-8fb219ce16aa ip route list table 167772417 default via 10.0.1.6 dev qr-ddbdc784-d7
这个表会将其转发给10.0.1.6,而这个IP就是在network node上的router_centralized_snat接口。
在network node的snat namespace中，我们可以看到这个接口。
$ sudo ip netns exec snat-0fbb351e-a65b-4790-a409-8fb219ce16aa iptables -nvL -t nat ... Chain neutron-l3-agent-snat (1 references) pkts bytes target prot opt in out source destination 0 0 SNAT all -- * * 10.0.1.0/24 0.0.0.0/0 to:172.24.4.4 0 0 SNAT all -- * * 10.0.2.0/24 0.0.0.0/0 to:172.24.4.4 ...
这里就和以前的L3类似，会将没有floating ip的包SNAT成一个172.24.4.4(DVR的网关臂)。这个过程是和以前L3类似的，不再累述。
参考：http://www.sxt.cn/u/756/blog/3168
(未完)
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原文地址：http://www.cnblogs.com/xingyun/p/4876083.html
