OpenFlow link capacity

在 Openflow 1.0中，對於每個Port的定義如下

/* Description of a physical port */
struct ofp_phy_port {
    uint16_t port_no;
    uint8_t hw_addr[OFP_ETH_ALEN];
    char name[OFP_MAX_PORT_NAME_LEN]; /* Null-terminated */
    uint32_t config; /* Bitmap of OFPPC_* flags. */
    uint32_t state; /* Bitmap of OFPPS_* flags. */
    /* Bitmaps of OFPPF_* that describe features. All bits zeroed if
    * unsupported or unavailable. */
    uint32_t curr; /* Current features. */
    uint32_t advertised; /* Features being advertised by the port. */
    uint32_t supported; /* Features supported by the port. */
    uint32_t peer; /* Features advertised by peer. */
};

從這個定義之中，可以注意到有ㄧ個欄位叫做curr,他是一個bitmaps的表達式，由ofp_port_features所組成

/* Features of physical ports available in a datapath. */
    enum ofp_port_features {
    OFPPF_10MB_HD = 1 << 0, /* 10 Mb half-duplex rate support. */
    OFPPF_10MB_FD = 1 << 1, /* 10 Mb full-duplex rate support. */
    OFPPF_100MB_HD = 1 << 2, /* 100 Mb half-duplex rate support. */
    OFPPF_100MB_FD = 1 << 3, /* 100 Mb full-duplex rate support. */
    OFPPF_1GB_HD = 1 << 4, /* 1 Gb half-duplex rate support. */
    OFPPF_1GB_FD = 1 << 5, /* 1 Gb full-duplex rate support. */
    OFPPF_10GB_FD = 1 << 6, /* 10 Gb full-duplex rate support. */
    OFPPF_COPPER = 1 << 7, /* Copper medium. */
    OFPPF_FIBER = 1 << 8, /* Fiber medium. */
    OFPPF_AUTONEG = 1 << 9, /* Auto-negotiation. */
    OFPPF_PAUSE = 1 << 10, /* Pause. */
    OFPPF_PAUSE_ASYM = 1 << 11 /* Asymmetric pause. */
};

這樣看起來我們可以透過features request的方式來取得switch上每一個port的capacity，因此做了下列實驗

環境建置

Controller: Floodlight
Network environment: mininet or OVS on PC

Expr 1

mn --controller=remote,ip=127.0.0.1, --topo tree,1
curl http://127.0.0.1:8080/wm/core/switch/all/features/json

{
  "00:00:00:00:00:00:00:01": {
    "actions": 4095,
    "buffers": 256,
    "capabilities": 199,
    "datapathId": "00:00:00:00:00:00:00:01",
    "length": 176,
    "ports": [
      {
        "advertisedFeatures": 0,
        "config": 0,
        "currentFeatures": 192,
        "hardwareAddress": "32:38:53:8a:27:42",
        "name": "s1-eth1",
        "peerFeatures": 0,
        "portNumber": 1,
        "state": 0,
        "supportedFeatures": 0
      },
      {
        "advertisedFeatures": 0,
        "config": 0,
        "currentFeatures": 192,
        "hardwareAddress": "8a:5d:09:2f:cf:06",
        "name": "s1-eth2",
        "peerFeatures": 0,
        "portNumber": 2,
        "state": 0,
        "supportedFeatures": 0
      },
      {
        "advertisedFeatures": 0,
        "config": 0,
        "currentFeatures": 0,
        "hardwareAddress": "7e:00:4e:66:4d:45",
        "name": "s1",
        "peerFeatures": 0,
        "portNumber": 65534,
        "state": 0,
        "supportedFeatures": 0
      }
    ],
    "tables": -2,
    "type": "FEATURES_REPLY",
    "version": 1,
    "xid": 7
  }
}

從回傳的訊息中可以看到，除了lo以外的currentFeatures都是192，192就是2^7+2^6,所以對應到ofp_port_features就是OFPPF_10GB_FD以及OFPPF_COPPER

Expr 2

這次使用了traffic control link可調整頻寬的link來使用，看看是否會有所變化
mn --controller=remote,ip=140.113.214.95,port=6633 --topo tree,1 --link tc,bw=100.0
curl http://127.0.0.1:8080/wm/core/switch/all/features/json

{
  "00:00:00:00:00:00:00:01": {
    "actions": 4095,
    "buffers": 256,
    "capabilities": 199,
    "datapathId": "00:00:00:00:00:00:00:01",
    "length": 176,
    "ports": [
      {
        "advertisedFeatures": 0,
        "config": 0,
        "currentFeatures": 192,
        "hardwareAddress": "32:38:53:8a:27:42",
        "name": "s1-eth1",
        "peerFeatures": 0,
        "portNumber": 1,
        "state": 0,
        "supportedFeatures": 0
      },
      {
        "advertisedFeatures": 0,
        "config": 0,
        "currentFeatures": 192,
        "hardwareAddress": "8a:5d:09:2f:cf:06",
        "name": "s1-eth2",
        "peerFeatures": 0,
        "portNumber": 2,
        "state": 0,
        "supportedFeatures": 0
      },
      {
        "advertisedFeatures": 0,
        "config": 0,
        "currentFeatures": 0,
        "hardwareAddress": "7e:00:4e:66:4d:45",
        "name": "s1",
        "peerFeatures": 0,
        "portNumber": 65534,
        "state": 0,
        "supportedFeatures": 0
      }
    ],
    "tables": -2,
    "type": "FEATURES_REPLY",
    "version": 1,
    "xid": 7
  }
}

可以看到完全沒有變化，不管有沒有設定tc link,這個currentFeatures的值依然是固定在10G，因此就很好奇會不會是這個featureRequest本身並沒有實作出來，因此換一個網路環境再試試看

Expr 3

這次就不使用mininet而是直接用一台實體PC配上OVS來跑跑看
curl http://127.0.0.1:8080/wm/core/switch/all/features/json

{
  "00:00:a0:36:9f:00:ed:04": {
    "actions": 4095,
    "buffers": 256,
    "capabilities": 199,
    "datapathId": "00:00:a0:36:9f:00:ed:04",
    "length": 272,
    "ports": [
      {
        "advertisedFeatures": 1711,
        "config": 0,
        "currentFeatures": 672,
        "hardwareAddress": "a0:36:9f:00:ed:06",
        "name": "eth3",
        "peerFeatures": 0,
        "portNumber": 3,
        "state": 0,
        "supportedFeatures": 1711
      },
      {
        "advertisedFeatures": 1711,
        "config": 0,
        "currentFeatures": 640,
        "hardwareAddress": "a0:36:9f:00:ed:05",
        "name": "eth2",
        "peerFeatures": 0,
        "portNumber": 2,
        "state": 1,
        "supportedFeatures": 1711
      },
      {
        "advertisedFeatures": 1711,
        "config": 0,
        "currentFeatures": 640,
        "hardwareAddress": "a0:36:9f:00:ed:07",
        "name": "eth4",
        "peerFeatures": 0,
        "portNumber": 4,
        "state": 1,
        "supportedFeatures": 1711
      },
      {
        "advertisedFeatures": 0,
        "config": 1,
        "currentFeatures": 0,
        "hardwareAddress": "a0:36:9f:00:ed:04",
        "name": "br0",
        "peerFeatures": 0,
        "portNumber": 65534,
        "state": 1,
        "supportedFeatures": 0
      },
      {
        "advertisedFeatures": 1711,
        "config": 0,
        "currentFeatures": 640,
        "hardwareAddress": "a0:36:9f:00:ed:04",
        "name": "eth1",
        "peerFeatures": 0,
        "portNumber": 1,
        "state": 1,
        "supportedFeatures": 1711
      }
    ],
    "tables": -1,
    "type": "FEATURES_REPLY",
    "version": 1,
    "xid": 4
  }
}

採用真正的網卡後，就會發現currentFeatures的值是有變化的，這代表OVS的確有實作這個功能，於是我就開始好奇，為什麼Mininet中得到的數值都是10G,tc link到底是什麼

Mininet

在仔細研究mininet的source code後，大致瞭解了整個運作流程
當mininet要在兩個switch間創造一條link的時候，是透過下列手段達成的
- ip link add name s1-eth1 type veth peer name s2-eth1 這種系統指令創造一個特殊的裝置veth，這兩個裝置的封包會彼此互通，因此就達成了link的功用
- 此時透過ethtool s1-eth1可以觀察到其中 Speed: 10000Mb/s這樣的設定，他的速度就是設定成10G
- 在OVS中會使用 struct ethtool_cmd這種結構來獲取port的相關資訊，這時候他會根據speed這個欄位來設定currentFeautres的數值
- 因此mininet創造出來的link預設都是10G，所以OVS那邊都會抓到10G的資訊
traffic control的部分則是透過系統的tc指令來做到速度限制的功能，所以不會動到每個port的設定

環境建置​

Expr 1​

Expr 2​

Expr 3​

Mininet​

環境建置

Expr 1

Expr 2

Expr 3

Mininet