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Preface

Floodlight中，最基本用來轉送封包的module就是Forwarding Module,這邊稍為介紹一下心得:

Architecture

Forwarding 擴充了 ForwardingBase, ForwardingBase位於/routing/底下，之後會再詳細介紹這個module. 其主要功能就是幫忙把一個route給送到對應的switches，透過flow-modify的封包來寫入flow-entry到每個路徑上的switch。 當有封包近來的時候就會呼叫processPacketInMessage此function ForwardingBase本身並沒有實作該function，把這判斷的部分交給其他的module處理，這邊就是由forwarding modules來處理。

Hight-Level Overview

當有一個PacketIn event送到controller時，Forwarding中會根據ㄧ些已經決定的decision (如firewall)來決定如何處理 如果沒有決定的話，就採用預設的行為處理

  1. Drop
  2. Flood (default for broadcast or multicast in Ethernet header)
  3. Forward (default)

Low-Level implementation

Drop​

  • Create Openflow Flow-Modify Packet with no action ( no action means drop)
  • Send Flow-Modify Packet to switch.

得到一個Openflow Flow-Modify類型的封包 OFFlowMod fm =(OFFlowMod) floodlightProvider.getOFMessageFactory().getMessage(OFType.FLOW_MOD);

設定一個Actions,然後不增加任何action,這樣就會事drop的行為 List<OFAction> actions = new ArrayList<OFAction>();

設定Flow-Modify Packet的ㄧ些欄位，譬如HardTimeout,IdleTimeout...,這邊沒有設定Command預設就是flow_add

fm.setCookie(cookie)
  .setHardTimeout((short) 0)
  .setIdleTimeout((short) 5)
  .setBufferId(OFPacketOut.BUFFER_ID_NONE)
  .setMatch(match)
  .setActions(actions)
  .setLengthU(OFFlowMod.MINIMUM_LENGTH);

把訊息藉由messageDamper送給switch messageDamper.write(sw, fm, cntx);

Flood​

  • Check the ingress port is allowed broadcast ( according broadcast tree)
  • Create Packout packet with Flood action
  • Send Packout to switch.

根據BroadCast Tree判斷發送PacketIn Event的{swtich,port}是否能夠廣播，避免造成broadcast storm

if (topology.isIncomingBroadcastAllowed(sw.getId(),
    pi.getInPort()) == false) {
    return;
}

創造一個Packet Out的封包 OFPacketOut po =(OFPacketOut) floodlightProvider.getOFMessageFactory().getMessage(OFType.PACKET_OUT)

創造actions,放入一個flood的action,根據ㄧ些property來決定要送到哪個logical port

List<OFAction> actions = new ArrayList<OFAction>();
if (sw.hasAttribute(IOFSwitch.PROP_SUPPORTS_OFPP_FLOOD)) {
    actions.add(new OFActionOutput(OFPort.OFPP_FLOOD.getValue(),
    (short)0xFFFF));
} else {
    actions.add(new OFActionOutput(OFPort.OFPP_ALL.getValue(),
    (short)0xFFFF));
}
po.setActions(actions);
po.setActionsLength((short) OFActionOutput.MINIMUM_LENGTH);

把封包的資料一併傳下去，然後flood 如果PacketIn是送bufferID而不是packetData的話，這邊是否要額外判斷???

byte[] packetData = pi.getPacketData();
poLength += packetData.length;
po.setPacketData(packetData);

把訊息藉由messageDamper送給switch messageDamper.write(sw, po, cntx);

Forward​

  • check we know the desination device
  • check source device and destination device are same cluseter
  • find all attach switch
  • find route between souce device and destination device
  • use forwardingBase's method to push a route to all swith which on route.

先取得source 跟 destination device 每個device 是用IP、MAC、VLAN來做為區別的 IDevice dstDevice = IDeviceService.fcStore.get(cntx, IDeviceService.CONTEXT_DST_DEVICE); IDevice srcDevice = IDeviceService.fcStore.get(cntx, IDeviceService.CONTEXT_SRC_DEVICE);

接下來根據pkacetIN進來的switch取得其所屬的cluster. Long srcIsland = topology.getL2DomainId(sw.getId());

去探訪destination device所連接到的switch,看看是否有跟發生PacketIn的switch是在同一個Cluster, 是的話才有辦法轉送，否則就Flood出去

for (SwitchPort dstDap : dstDevice.getAttachmentPoints()) {
    Long dstSwDpid = dstDap.getSwitchDPID();
    Long dstIsland = topology.getL2DomainId(dstSwDpid);`

if ((dstIsland != null) && dstIsland.equals(srcIsland))
on_same_island = true;

取得source / destination device所連接到的所有switch 目前還不是很清楚怎樣的情形下，可以一個device連接到多個switch 也許用hub吧

SwitchPort[] srcDaps = srcDevice.getAttachmentPoints(); SwitchPort[] dstDaps = dstDevice.getAttachmentPoints();`

利用routingEngine來取得兩個switch間的最短路徑 (dijstra) Route route = routingEngine.getRoute(srcDap.getSwitchDPID(),(short)srcDap.getPort(),dstDap.getSwitchDPID(), (short)dstDap.getPort(), 0);

接者透過ForwardingBase的pushRoute,會把路徑上所有的switch都發送一個Flow-Modify的封包 pushRoute(route, match, wildcard_hints, pi, sw.getId(), cookie,cntx, requestFlowRemovedNotifn, false, OFFlowMod.OFPFC_ADD);

處理完這組switch後，繼續嘗試其他連接的switch iSrcDaps++; iDstDaps++;

結論

Forwarding是個很基本的module,原始的情況下就是把封包給forward或是flood的而已， 目前裡面的設計是希望能夠取得多個attach points,但是我目前嘗試各種拓樸，都沒有辦法讓一個device連接到多個switch,不知道是否要使用hub之類的東西來完成，這部分要再嘗試看看。