2019 SDN第三次上机作业

作业要求：

• 利用Mininet仿真平台构建给定的网络拓扑，配置主机h1和h2的IP地址（h1:10.0.0.1，h2:10.0.0.2），测试两台主机之间的网络连通性；
• 利用Wireshark工具，捕获拓扑中交换机与控制器之间的通信数据，对OpenFlow协议类型的各类报文（hello, features_request, features_reply, set_config, packet_in, packet_out等）进行分析，对照wireshark截图写出你的分析内容；
• 作业博客链接：https://edu.cnblogs.com/campus/fzu/fzusdn2019/homework/9968

1. 利用Mininet仿真平台构建如下图所示的网络拓扑，配置主机h1和h2的IP地址（h1:10.0.0.1，h2:10.0.0.2），测试两台主机之间的网络连通性

具体操作步骤与截图说明：

• 打开终端启动wireshark工具,在wireshark中使用any捕获过滤器（避免实验过程中没有捕捉到拓扑网络建立过程中的某些报文）

• 使用miniedit仿真工具创建拓扑，并设置主机h1的IP地址为10.0.0.1，设置主机h2的IP地址为10.0.0.2，勾选start CLI，并支持OpenFlow 1.0 1.1 1.2 1.3，Controller选择默认的openflow reference

2. 利用Wireshark工具，捕获拓扑中交换机与控制器之间的通信数据，对OpenFlow协议类型的各类报文（hello, features_request, features_reply, set_config, packet_in, packet_out等）进行分析，对照wireshark截图写出你的分析内容

报文分析

• hello

交换机56894端口 --> 控制器6633端口（最高支持OpenFlow 1.3协议）

控制器6633端口 --> 交换机56894端口（最高支持OpenFlow 1.0协议）

交换机与控制器并使用OpenFlow 1.0协议（向下兼容）

• Features Request

控制器6633端口（请求发送特征信息）-->交换机56894端口

• Set Config

控制器6633端口（按照控制器发送的flag和max bytes of packet进行配置）-->交换机56894

• Features Reply

交换机56894端口（回复特征信息)-->控制器6633端口

​Features 消息包括 OpenFlow Header 和 Features Reply Message
​ 对照Features Reply Message结构

struct ofp_switch_features{
    struct ofp_header header;
    uint64_t datapath_id; /*唯一标识 id 号*/
    uint32_t n_buffers; /*交缓冲区可以缓存的最大数据包个数*/
    uint8_t n_tables; /*流表数量*/
    uint8_t pad[3]; /*align to 64 bits*/
    uint32_t capabilities; /*支持的特殊功能，具体见 ofp_capabilities*/
    uint32_t actions; /*支持的动作，具体见 ofp_actions_type*/
    struct ofp_phy_port ports[0]; /*物理端口描述列表，具体见 ofp_phy_port*/
};

对应到抓取到的报文，逐项查看报文内容

OpenFlow 1.0
    .000 0001 = Version: 1.0 (0x01)
    Type: OFPT_FEATURES_REPLY (6)
    Length: 176
    Transaction ID: 1249319388
    Datapath unique ID: 0x0000000000000001
        MAC addr: 00:00:00_00:00:00 (00:00:00:00:00:00)
        Implementers part: 0x0001
    n_buffers: 256
    n_tables: 254
    Pad: 000000
    capabilities: 0x000000c7
        .... .... .... .... .... .... .... ...1 = Flow statistics: True
        .... .... .... .... .... .... .... ..1. = Table statistics: True
        .... .... .... .... .... .... .... .1.. = Port statistics: True
        .... .... .... .... .... .... .... 0... = Group statistics: False
        .... .... .... .... .... .... ..0. .... = Can reassemble IP fragments: False
        .... .... .... .... .... .... .1.. .... = Queue statistics: True
        .... .... .... .... .... ...0 .... .... = Switch will block looping ports: False
    actions: 0x00000fff
        .... .... .... .... .... .... .... ...1 = Output to switch port: True
        .... .... .... .... .... .... .... ..1. = Set the 802.1q VLAN id: True
        .... .... .... .... .... .... .... .1.. = Set the 802.1q priority: True
        .... .... .... .... .... .... .... 1... = Strip the 802.1q header: True
        .... .... .... .... .... .... ...1 .... = Ethernet source address: True
        .... .... .... .... .... .... ..1. .... = Ethernet destination address: True
        .... .... .... .... .... .... .1.. .... = IP source address: True
        .... .... .... .... .... .... 1... .... = IP destination address: True
        .... .... .... .... .... ...1 .... .... = IP ToS (DSCP field, 6 bits): True
        .... .... .... .... .... ..1. .... .... = TCP/UDP source port: True
        .... .... .... .... .... .1.. .... .... = TCP/UDP destination port: True
        .... .... .... .... .... 1... .... .... = Output to queue: True
    Port data 1
        Port number: 1
        HW Address: b2:0e:a0:79:55:66 (b2:0e:a0:79:55:66)
        Port Name: s1-eth1
        Config flags: 0x00000000
        State flags: 0x00000000
        Current features: 0x000000c0
        Advertised features: 0x00000000
        Features supported: 0x00000000
        Features advertised by peer: 0x00000000
    Port data 2
        Port number: 65534
        HW Address: 36:4c:9b:3e:44:46 (36:4c:9b:3e:44:46)
        Port Name: s1
        Config flags: 0x00000001
        State flags: 0x00000001
        Current features: 0x00000000
        Advertised features: 0x00000000
        Features supported: 0x00000000
        Features advertised by peer: 0x00000000
    Port data 3
        Port number: 2
        HW Address: 7e:ff:63:0f:59:51 (7e:ff:63:0f:59:51)
        Port Name: s1-eth2
        Config flags: 0x00000000
        State flags: 0x00000000
        Current features: 0x000000c0
        Advertised features: 0x00000000
        Features supported: 0x00000000
        Features advertised by peer: 0x00000000

• Packet_in

交换机56894端口-->控制器6633端口

结合Packet_in的结构

struct ofp_packet_in 
{
    struct ofp_header header;
    uint32_t buffer_id; /*Packet-in消息所携带的数据包在交换机缓存区中的ID*/
    uint16_t total_len; /*data字段的长度*/
    uint16_t in_port; /*数据包进入交换机时的端口号*/
    uint8_t reason; /*发送Packet-in消息的原因，具体见 ofp_packet_in_reason*/
    uint8_t pad;
    uint8_t data[0]; /*携带的数据包*/
};

分析抓取的数据包，可以发现是因为交换机发现此时自己并没有匹配的流表（Reason: No matching flow (table-miss flow entry) (0)），所以要问控制器如何处理

OpenFlow 1.0
    .000 0001 = Version: 1.0 (0x01)
    Type: OFPT_PACKET_IN (10)
    Length: 104
    Transaction ID: 0
    Buffer Id: 0x00000100
    Total length: 86
    In port: 1
    Reason: No matching flow (table-miss flow entry) (0)
    Pad: 00
    Ethernet II, Src: 76:78:c7:38:d0:de (76:78:c7:38:d0:de), Dst: IPv6mcast_ff:38:d0:de (33:33:ff:38:d0:de)
        Destination: IPv6mcast_ff:38:d0:de (33:33:ff:38:d0:de)
        Source: 76:78:c7:38:d0:de (76:78:c7:38:d0:de)
        Type: IPv6 (0x86dd)
    Internet Protocol Version 6, Src: ::, Dst: ff02::1:ff38:d0de
        0110 .... = Version: 6
        .... 0000 0000 .... .... .... .... .... = Traffic Class: 0x00 (DSCP: CS0, ECN: Not-ECT)
            .... 0000 00.. .... .... .... .... .... = Differentiated Services Codepoint: Default (0)
            .... .... ..00 .... .... .... .... .... = Explicit Congestion Notification: Not ECN-Capable Transport (0)
        .... .... .... 0000 0000 0000 0000 0000 = Flow Label: 0x00000
        Payload Length: 32
        Next Header: ICMPv6 (58)
        Hop Limit: 255
        Source: ::
        Destination: ff02::1:ff38:d0de
    Internet Control Message Protocol v6
        Type: Neighbor Solicitation (135)
        Code: 0
        Checksum: 0xf163 [correct]
        [Checksum Status: Good]
        Reserved: 00000000
        Target Address: fe80::7478:c7ff:fe38:d0de
        ICMPv6 Option (Nonce)
            Type: Nonce (14)
            Length: 1 (8 bytes)
            Nonce: 710398f79618

• Packet_out

控制器6633端口-->交换机56894端口
结合Packet_out的结构

struct ofp_packet_out 
{
    struct ofp_header header;
    uint32_t buffer_id; /*交换机缓存区id，如果为-1则指定的为packet-out消息携带的data字段*/
    uint16_t in_port; /*如果buffer_id为‐1，并且action列表中指定了Output=TABLE的动作,in_port将作为data段数据包的额外匹配信息进行流表查询*/
    uint16_t actions_len; /*action列表的长度，可以用来区分actions和data段*/
    struct ofp_action_header actions[0]; /*动作列表*/
    uint8_t data[0]; /*数据缓存区，可以存储一个以太网帧，可选*/
}

告诉输出到交换机的65531端口

OpenFlow 1.0
    .000 0001 = Version: 1.0 (0x01)
    Type: OFPT_PACKET_OUT (13)
    Length: 24
    Transaction ID: 0
    Buffer Id: 0x00000100
    In port: 1
    Actions length: 8
    Actions type: Output to switch port (0)
    Action length: 8
    Output port: 65531
    Max length: 0

h1 ping h2

• packet_in

• flow_mod

结合flow_mod结构

struct ofp_flow_mod 
{
    struct ofp_header header;
    struct ofp_match match; /*流表的匹配域*/ 
    uint64_t cookie; /*流表项标识符*/
    uint16_t command; /*可以是ADD,DELETE,DELETE-STRICT,MODIFY,MODIFY-STRICT*/
    uint16_t idle_timeout; /*空闲超时时间*/
    uint16_t hard_timeout; /*最大生存时间*/
    uint16_t priority; /*优先级，优先级高的流表项优先匹配*/
    uint32_t buffer_id; /*缓存区ID ,用于指定缓存区中的一个数据包按这个消息的action列表处理*/  
    uint16_t out_port; /*如果这条消息是用于删除流表则需要提供额外的匹配参数*/
    uint16_t flags; /*标志位，可以用来指示流表删除后是否发送flow‐removed消息，添加流表时是否检查流表重复项，添加的流表项是否为应急流表项。*/
    struct ofp_action_header actions[0]; /*action列表*/
};

分析抓取的flow_mod数据包，控制器通过6633端口向交换机56894端口、交换机56896端口下发流表项，指导数据的转发处理

把控制器从openflow reference改成ovs controller

• hello

在hello报文中可以发现控制器支持的OpenFlow版本从1.0变成了1.3，因此，经过协商交换机和控制器之间将通过1.3版本的OpenFlow协议进行通信

• flow_mod

双方协商使用OpenFlow 1.3进行通信

3.实验总结：

​通过这次实验，进一步熟悉了wireshark这一抓包工具的使用，捕获OpenFlow协议中的各类报文（hello,features_request,features_reply,set_config, packet_in, packet_out等等）。对在openflow协议下交换机和控制器的工作原理有了一定的了解。