Ryu控制器深入实践：SDN网络管理

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"Ryu控制器是SDN（Software-Defined Networking，软件定义网络）领域中的一个开源控制器，它提供了一个框架来实现各种网络服务。这本书籍详细介绍了如何使用Ryu来构建网络元素，如交换机、流量监控器、REST API集成、链路聚合以及生成树协议等。" 在SDN架构中，Ryu控制器扮演着核心角色，它负责处理来自网络设备（如OpenFlow交换机）的数据流，并做出相应的决策。以下是基于标题和描述中涉及的关键知识点的详细解释： 1. **Ryu控制器**：Ryu是基于事件驱动的SDN控制器，支持OpenFlow 1.3及以上版本，提供了模块化的结构，允许开发者轻松创建新的网络应用。Ryu的核心特性包括高性能、可扩展性和灵活性。 2. **OpenFlow协议**：OpenFlow是SDN的基础，它定义了控制器与数据平面设备之间的通信协议。在Ryu中，OpenFlow协议用于控制流表项，通过`Match`字段指定匹配条件，`Instructions`字段定义匹配后的动作，如转发、丢弃或修改数据包。 3. **SwitchingHub**：这部分内容讲述了如何使用Ryu实现基本的交换机功能。SwitchingHub是一个简单的网络元素，可以接收并转发数据包。通过OpenFlow，Ryu能够动态配置交换机的行为，如设置流表规则。 4. **TrafficMonitor**：Ryu可以用来实现网络流量监控，这有助于识别网络的瓶颈和异常。通过编程，可以收集并分析网络的流量统计，提供实时的网络健康状况报告。 5. **RESTLinkage**：Ryu支持REST API集成，这意味着可以通过HTTP请求来控制网络，增加了网络管理的便捷性。这部分描述了如何使用Ryu实现带REST API的交换机，使得网络操作可以远程进行。 6. **LinkAggregation**：链路聚合是提高网络带宽和冗余的一种方法，Ryu提供了实现链路聚合的功能。通过结合多条物理链路，可以创建逻辑上的更高速度的连接，同时增强网络的可靠性。 7. **SpanningTree**：生成树协议（如IEEE 802.1D）用于防止网络中的循环路径，确保数据包的正确传输。Ryu能够实现OpenFlow版本的生成树协议，通过配置网络拓扑来避免环路，同时保持网络的连通性。这本书籍的每一章节都深入浅出地介绍了Ryu控制器在不同场景下的应用，对于理解和掌握SDN的实践具有很高的价值。通过学习这些内容，读者不仅可以理解Ryu的基本工作原理，还能掌握如何开发自己的SDN应用程序。

RYU SDN Framework, Release 1.0

# install a flow to avoid packet_in next time.

if out_port != ofproto.OFPP_FLOOD:

match = parser.OFPMatch(in_port=in_port, eth_dst=dst)

self.add_flow(datapath, 1, match, actions)

# ...

If the destination MAC address is found, an entry is added to the ﬂow table of the OpenFlow switch.

As with addition of the Table-miss ﬂow entry, specify match and action, and execute add_ﬂow() to add a ﬂow

entry.

Unlike the Table-miss ﬂow entry, set conditions for match this time. Implementation of the switching hub this

time, the receive port (in_port) and destination MAC address (eth_dst) have been speciﬁed. For example, packets

addressed to host B received by port 1 is the target.

For the ﬂow entry this time, the priority is speciﬁed to 1. The greater the value, the higher the priority, therefore,

the ﬂow entry added here will be evaluated before the Table-miss ﬂow entry.

Based on the summary including the aforementioned actions, add the following entry to the ﬂow table.

Transfer packets addressed to host B (the destination MAC address is B) received by port 1 to port 4.

Hint: With OpenFlow, a logical output port called NORMAL is prescribed in option and when NORMAL is speciﬁed for the

output port, the L2/L3 function of the switch is used to process the packets. That means, by instructing to output all packets

to the NORMAL port, it is possible to make the switch operate as a switching hub. However, we implement each processing

using OpenFlow.

Adding Processing of Flow Entry

Processing of the Packet-In handler has not been done yet but here take a look at the method to add ﬂow entries.

def add_flow(self, datapath, priority, match, actions):

ofproto = datapath.ofproto

parser = datapath.ofproto_parser

# construct flow_mod message and send it.

inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,

actions)]

# ...

For ﬂow entries, set match that indicates the target packet conditions, and instruction that indicates the operation

on the packet, entry priority level, and effective time.

In the switching hub implementation, Apply Actions is used for the instruction to set so that the speciﬁed action

is immediately used.

Finally, add an entry to the ﬂow table by issuing the Flow Mod message.

def add_flow(self, datapath, priority, match, actions):

# ...

mod = parser.OFPFlowMod(datapath=datapath, priority=priority,

match=match, instructions=inst)

datapath.send_msg(mod)

The class corresponding to the Flow Mod message is the OFPFlowMod class. The instance of the OFPFlowMod

class is generated and the message is sent to the OpenFlow switch using the Datapath.send_msg() method.

There are many arguments of constructor of the OFPFlowMod class. Many of them generally can be the default

as is. Inside the parenthesis is the default.

datapath

This is the Datapath class instance supporting the OpenFlow switch subject to ﬂow table operation.

Normally, specify the one acquired from the event passed to the handler such as the Packet-In mes-

sage.

12 Chapter 2. Switching Hub

RYU SDN Framework, Release 1.0

cookie (0)

An optional value speciﬁed by the controller and can be used as a ﬁlter condition when updating or

deleting entries. This is not used for packet processing.

cookie_mask (0)

When updating or deleting entries, if a value other than 0 is speciﬁed, it is used as the ﬁlter of the

operation target entry using the cookie value of the entry.

table_id (0)

Speciﬁes the table ID of the operation target ﬂow table.

command (ofproto_v1_3.OFPFC_ADD)

Specify whose operation is to be performed.

Value Explanation

OFPFC_ADD Adds new ﬂow entries.

OFPFC_MODIFY Updates ﬂow entries.

OFPFC_MODIFY_STRICT Update strictly matched ﬂow entries

OFPFC_DELETE Deletes ﬂow entries.

OFPFC_DELETE_STRICT Deletes strictly matched ﬂow entries.

idle_timeout (0)

Speciﬁes the validity period of this entry, in seconds. If the entry is not referenced and the time

speciﬁed by idle_timeout elapses, that entry is deleted. When the entry is referenced, the elapsed

time is reset.

When the entry is deleted, a Flow Removed message is sent to the controller.

hard_timeout (0)

Speciﬁes the validity period of this entry, in seconds. Unlike idle_timeout, with hard_timeout, even

though the entry is referenced, the elapsed time is not reset. That is, regardless of the reference of the

entry, the entry is deleted when the speciﬁed time elapsed.

As with idle_timeout, when the entry is deleted, a Flow Removed message is sent.

priority (0)

Speciﬁes the priority order of this entry. The greater the value, the higher the priority.

buffer_id (ofproto_v1_3.OFP_NO_BUFFER)

Speciﬁes the buffer ID of the packet buffered on the OpenFlow switch. The buffer ID is notiﬁed in

the packet-In message and when the speciﬁed processing is the same as when two messages are sent,

i.e., the Packet-Out message for which OFPP_TABLE is speciﬁed for the output port and Flow Mod

message. This is ignored when the command is OFPFC_DELETE or OFPFC_DELETE_STRICT.

When the buffer ID is not speciﬁed, set OFP_NO_BUFFER.

out_port (0)

If the command is OFPFC_DELETE or OFPFC_DELETE_STRICT, the target entry is ﬁltered by the

output port. If the command is OFPFC_ADD, OFPFC_MODIFY, or OFPFC_MODIFY_STRICT, it

is ignored.

To disable ﬁltering by the output port, specify OFPP_ANY.

out_group (0)

As with out_port, ﬁlters by the output group.

To disable, specify OFPG_ANY.

ﬂags (0)

2.3. Implementation of Switching Hub Using Ryu 13

RYU SDN Framework, Release 1.0

You can specify the following combinations of ﬂags.

Value Explanation

OFPFF_SEND_FLOW_REM Issues the Flow Removed message to the controller when this

entry is deleted.

OFPFF_CHECK_OVERLAP When the command is OFPFC_ADD, checks duplicated entries.

If duplicated entries are found, Flow Mod fails and an error is

returned.

OFPFF_RESET_COUNTS Resets the packet counter and byte counter of the relevant entry.

OFPFF_NO_PKT_COUNTS Disables the packet counter of this entry.

OFPFF_NO_BYT_COUNTS Disables the byte counter of this entry.

match (None)

Speciﬁes match.

instructions ([])

Speciﬁes a list of instructions.

Packet Transfer

Now we return to the Packet-In handler and explain about ﬁnal processing.

Regardless whether the destination MAC address is found from the MAC address table, at the end the Packet-Out

message is issued and received packets are transferred.

def _packet_in_handler(self, ev):

# ...

# construct packet_out message and send it.

out = parser.OFPPacketOut(datapath=datapath,

buffer_id=ofproto.OFP_NO_BUFFER,

in_port=in_port, actions=actions,

data=msg.data)

datapath.send_msg(out)

The class corresponding to the Packet-Out message is OFPPacketOut class.

The arguments of the constructor of OFPPacketOut are as follows:

datapath

Speciﬁes the instance of the Datapath class corresponding to the OpenFlow switch.

buffer_id

Speciﬁes the buffer ID of the packets buffered on the OpenFlow. If not buffered, OFP_NO_BUFFER

is speciﬁed.

in_port

Speciﬁes the port that received packets. if it is not the received packet, OFPP_CONTROLLER is

speciﬁed.

actions

Speciﬁes the list of actions.

data

Speciﬁes the binary data of packets. This is used when OFP_NO_BUFFER is speciﬁed for buffer_id.

When the OpenFlow switch’s buffer is used, this is omitted.

In the switching hub implementation, buffer_id of the Packet-In message has been speciﬁed for buffer_id. If the

buffer-id of the Packet-In message has been disabled, the received packet of Packet-In is speciﬁed for data to send

the packets.

14 Chapter 2. Switching Hub

RYU SDN Framework, Release 1.0

flows: 0

port 0: ovs-system (internal)

port 1: s1 (internal)

port 2: s1-eth1

port 3: s1-eth2

port 4: s1-eth3

Switch (bridge) s1 has been created and three ports corresponding to hosts have been added.

Next, set 1.3 for the OpenFlow version.

switch: s1:

# ovs-vsctl set Bridge s1 protocols=OpenFlow13

Let’s check the empty ﬂow table.

switch: s1:

# ovs-ofctl -O OpenFlow13 dump-flows s1

OFPST_FLOW reply (OF1.3) (xid=0x2):

The ovs-ofctl command needs to specify the OpenFlow version to be used as an option. The default is Open-

Flow10.

2.4.1 Executing the Switching Hub

Preparation is now done and we will run the Ryu application.

From the xterm for which the window title is “controller: c0 (root)”, execute the following commands.

controller: c0:

# ryu-manager --verbose ryu.app.example_switch_13

loading app ryu.app.example_switch_13

loading app ryu.controller.ofp_handler

instantiating app ryu.app.example_switch_13 of ExampleSwitch13

instantiating app ryu.controller.ofp_handler of OFPHandler

BRICK ExampleSwitch13

CONSUMES EventOFPPacketIn

CONSUMES EventOFPSwitchFeatures

BRICK ofp_event

PROVIDES EventOFPPacketIn TO {'ExampleSwitch13': set(['main'])}

PROVIDES EventOFPSwitchFeatures TO {'ExampleSwitch13': set(['config'])}

CONSUMES EventOFPErrorMsg

CONSUMES EventOFPHello

CONSUMES EventOFPEchoRequest

CONSUMES EventOFPEchoReply

CONSUMES EventOFPPortStatus

CONSUMES EventOFPSwitchFeatures

CONSUMES EventOFPPortDescStatsReply

connected socket:<eventlet.greenio.base.GreenSocket object at 0x7f1239937a90> address

:('127.0.0.1', 37898)

hello ev <ryu.controller.ofp_event.EventOFPHello object at 0x7f1239927d50>

move onto config mode

EVENT ofp_event->ExampleSwitch13 EventOFPSwitchFeatures

switch features ev version=0x4,msg_type=0x6,msg_len=0x20,xid=0xea43ed30,OFPSwitchFeatures(

auxiliary_id=0,capabilities=79,datapath_id=1,n_buffers=256,n_tables=254)

move onto main mode

It may take time to connect to OVS but after you wait for a while, as shown above...

connected socket:<....

hello ev ...

...

move onto main mode

16 Chapter 2. Switching Hub

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