一般搭建成功了opentack后，都会按照文档的这样创建网络

Scenario 1: one tenant, two networks, one router

Scenario 2: two tenants, two networks, two routers

然而neutron号称软件定义网络，可否创建更复杂的拓扑图

我创建了上面的三个网络，每个网络都运行一个主机，网络1和网络2，并不直接相连，但是通过网络2相连。

对于主机net1，由于网络只有一个路由器，所以gateway只能是它

root@net1:/home/ubuntu# ip addr

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

inet 127.0.0.1/8 scope host lo

inet6 ::1/128 scope host

valid_lft forever preferred_lft forever

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000

link/ether fa:16:3e:f2:68:34 brd ff:ff:ff:ff:ff:ff

inet 10.0.0.2/24 brd 10.0.0.255 scope global eth0

inet6 fe80::f816:3eff:fef2:6834/64 scope link

valid_lft forever preferred_lft forever

root@net1:/home/ubuntu# route -n

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 10.0.0.1 0.0.0.0 UG 100 0 0 eth0

10.0.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

对于主机net3，所在的网络业只有一个路由器，所以gateway也只能是它

root@net3:/home/ubuntu# ip addr

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

inet 127.0.0.1/8 scope host lo

inet6 ::1/128 scope host

valid_lft forever preferred_lft forever

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000

link/ether fa:16:3e:73:2b:1f brd ff:ff:ff:ff:ff:ff

inet 10.0.2.2/24 brd 10.0.2.255 scope global eth0

inet6 fe80::f816:3eff:fe73:2b1f/64 scope link

valid_lft forever preferred_lft forever

root@net3:/home/ubuntu# route -n

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 10.0.2.1 0.0.0.0 UG 100 0 0 eth0

10.0.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

比较纠结的是主机net2，它的网络上有两个路由器，默认gateway只能是一个，那它如何才能ping通两面的主机呢，必须手动添加路由器。

root@net2:/home/ubuntu# ip addr

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN

link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

inet 127.0.0.1/8 scope host lo

inet6 ::1/128 scope host

valid_lft forever preferred_lft forever

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000

link/ether fa:16:3e:3c:65:ad brd ff:ff:ff:ff:ff:ff

inet 10.0.1.4/24 brd 10.0.1.255 scope global eth0

inet6 fe80::f816:3eff:fe3c:65ad/64 scope link

valid_lft forever preferred_lft forever

root@net2:/home/ubuntu# route -n

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

0.0.0.0 10.0.1.1 0.0.0.0 UG 100 0 0 eth0

10.0.0.0 10.0.1.1 255.255.255.0 UG 0 0 0 eth0

10.0.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

10.0.2.0 10.0.1.2 255.255.255.0 UG 0 0 0 eth0

到不同的网络，gateway不一样。

最后的问题是，net1和net3之间怎么通信，如果neutron创建的路由器支持动态路由就好了，一般通过routed或者gated，相邻的路由器router1和router2可以相互同步路由表，这样router1才可能知道，在router2的另一端，还有一个网络，反之亦然。

https://blueprints.launchpad.net/neutron/+spec/bgp-dynamic-routing

然而这个好像还没实现，所以要想net1和net3之间通信，需要手动添加路由表到路由器

我们修改router1的路由表

root@escto-bj-hp-z620:~# ip netns exec qrouter-8fd947fc-2b5b-40a3-b16e-72aabb001f2d route -n

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

10.0.0.0 0.0.0.0 255.255.255.0 U 0 0 0 qr-bbbc67c3-81

10.0.1.0 0.0.0.0 255.255.255.0 U 0 0 0 qr-10b0d153-4c

10.0.2.0 10.0.1.2 255.255.255.0 UG 0 0 0 qr-10b0d153-4c

再来修改router2的路由表

root@escto-bj-hp-z620:~# ip netns exec qrouter-d2c831c9-44ff-43dd-8c9d-2dc42370c2fd route -n

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

10.0.0.0 10.0.1.1 255.255.255.0 UG 0 0 0 qr-ad73f294-6d

10.0.1.0 0.0.0.0 255.255.255.0 U 0 0 0 qr-ad73f294-6d

10.0.2.0 0.0.0.0 255.255.255.0 U 0 0 0 qr-866838bd-d7

这样相互就ping通了

通过API创建路由表

https://blueprints.launchpad.net/neutron/+spec/quantum-l3-routes