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L2Switch Developer Guide

Overview

The L2Switch project provides Layer2 switch functionality.

L2Switch Architecture

  • Packet Handler
    • Decodes the packets coming to the controller and dispatches them appropriately
  • Loop Remover
    • Removes loops in the network
  • Arp Handler
    • Handles the decoded ARP packets
  • Address Tracker
    • Learns the Addresses (MAC and IP) of entities in the network
  • Host Tracker
    • Tracks the locations of hosts in the network
  • L2Switch Main
    • Installs flows on each switch based on network traffic

Key APIs and Interfaces

  • Packet Handler
  • Loop Remover
  • Arp Handler
  • Address Tracker
  • Host Tracker
  • L2Switch Main

Packet Dispatcher

Classes

  • AbstractPacketDecoder
    • Defines the methods that all decoders must implement
  • EthernetDecoder
    • The base decoder which decodes the packet into an Ethernet packet
  • ArpDecoder, Ipv4Decoder, Ipv6Decoder
    • Decodes Ethernet packets into the either an ARP or IPv4 or IPv6 packet

Further development

There is a need for more decoders. A developer can write

  • A decoder for another EtherType, i.e. LLDP.
  • A higher layer decoder for the body of the IPv4 packet or IPv6 packet, i.e. TCP and UDP.

How to write a new decoder

  • extends AbstractDecoder<A, B>
    • A refers to the notification that the new decoder consumes
    • B refers to the notification that the new decoder produces
  • implements xPacketListener
    • The new decoder must specify which notification it is listening to
  • canDecode method
    • This method should examine the consumed notification to see whether the new decoder can decode the contents of the packet
  • decode method
    • This method does the actual decoding of the packet

Loop Remover

Classes

  • LoopRemoverModule
    • Reads config subsystem value for is-install-lldp-flow
      • If is-install-lldp-flow is true, then an InitialFlowWriter is created
    • Creates and initializes the other LoopRemover classes
  • InitialFlowWriter
    • Only created when is-install-lldp-flow is true
    • Installs a flow, which forwards all LLDP packets to the controller, on each switch
  • TopologyLinkDataChangeHandler
    • Listens to data change events on the Topology tree
    • When these changes occur, it waits graph-refresh-delay seconds and then tells NetworkGraphImpl to update
    • Writes an STP (Spanning Tree Protocol) status of “forwarding” or “discarding” to each link in the Topology data tree
      • Forwarding links can forward packets.
      • Discarding links cannot forward packets.
  • NetworkGraphImpl
    • Creates a loop-free graph of the network

Configuration

  • graph-refresh-delay
    • Used in TopologyLinkDataChangeHandler
    • A higher value has the advantage of doing less graph updates, at the potential cost of losing some packets because the graph didn’t update immediately.
    • A lower value has the advantage of handling network topology changes quicker, at the cost of doing more computation.
  • is-install-lldp-flow
    • Used in LoopRemoverModule
    • “true” means a flow that sends all LLDP packets to the controller will be installed on each switch
    • “false” means this flow will not be installed
  • lldp-flow-table-id
    • The LLDP flow will be installed on the specified flow table of each switch
  • lldp-flow-priority
    • The LLDP flow will be installed with the specified priority
  • lldp-flow-idle-timeout
    • The LLDP flow will timeout (removed from the switch) if the flow doesn’t forward a packet for x seconds
  • lldp-flow-hard-timeout
    • The LLDP flow will timeout (removed from the switch) after x seconds, regardless of how many packets it is forwarding

Further development

No suggestions at the moment.

Validating changes to Loop Remover

STP Status information is added to the Inventory data tree.

  • A status of “forwarding” means the link is active and packets are flowing on it.
  • A status of “discarding” means the link is inactive and packets are not sent over it.

The STP status of a link can be checked through a browser or a REST Client.

http://10.194.126.91:8080/restconf/operational/opendaylight-inventory:nodes/node/openflow:1/node-connector/openflow:1:2

The STP status should still be there after changes are made.

Arp Handler

Classes

  • ArpHandlerModule
    • Reads config subsystem value for is-proactive-flood-mode
      • If is-proactive-flood-mode is true, then a ProactiveFloodFlowWriter is created
      • If is-proactive-flood-mode is false, then an InitialFlowWriter is created
  • ProactiveFloodFlowWriter
    • Only created when is-proactive-flood-mode is true
    • Installs a flood flow on each switch. With this flood flow, a packet that doesn’t match any other flows will be flooded/broadcast from that switch.
  • InitialFlowWriter
    • Only created when is-proactive-flood-mode is false
    • Installs a flow, which sends all ARP packets to the controller, on each switch
  • ArpPacketHandler
    • Only created when is-proactive-flood-mode is false
    • Handles and processes the controller’s incoming ARP packets
    • Uses PacketDispatcher to send the ARP packet back into the network
  • PacketDispatcher
    • Only created when is-proactive-flood-mode is false
    • Sends packets out to the network
    • Uses InventoryReader to determine which node-connector to a send a packet on
  • InventoryReader
    • Only created when is-proactive-flood-mode is false
    • Maintains a list of each switch’s node-connectors

Configuration

  • is-proactive-flood-mode
    • “true” means that flood flows will be installed on each switch. With this flood flow, each switch will flood a packet that doesn’t match any other flows.
      • Advantage: Fewer packets are sent to the controller because those packets are flooded to the network.
      • Disadvantage: A lot of network traffic is generated.
    • “false” means the previously mentioned flood flows will not be installed. Instead an ARP flow will be installed on each switch that sends all ARP packets to the controller.
      • Advantage: Less network traffic is generated.
      • Disadvantage: The controller handles more packets (ARP requests & replies) and the ARP process takes longer than if there were flood flows.
  • flood-flow-table-id
    • The flood flow will be installed on the specified flow table of each switch
  • flood-flow-priority
    • The flood flow will be installed with the specified priority
  • flood-flow-idle-timeout
    • The flood flow will timeout (removed from the switch) if the flow doesn’t forward a packet for x seconds
  • flood-flow-hard-timeout
    • The flood flow will timeout (removed from the switch) after x seconds, regardless of how many packets it is forwarding
  • arp-flow-table-id
    • The ARP flow will be installed on the specified flow table of each switch
  • arp-flow-priority
    • The ARP flow will be installed with the specified priority
  • arp-flow-idle-timeout
    • The ARP flow will timeout (removed from the switch) if the flow doesn’t forward a packet for x seconds
  • arp-flow-hard-timeout
    • The ARP flow will timeout (removed from the switch) after arp-flow-hard-timeout seconds, regardless of how many packets it is forwarding

Further development

The ProactiveFloodFlowWriter needs to be improved. It does have the advantage of having less traffic come to the controller; however, it generates too much network traffic.

Address Tracker

Classes

  • AddressTrackerModule
    • Reads config subsystem value for observe-addresses-from
    • If observe-addresses-from contains “arp”, then an AddressObserverUsingArp is created
    • If observe-addresses-from contains “ipv4”, then an AddressObserverUsingIpv4 is created
    • If observe-addresses-from contains “ipv6”, then an AddressObserverUsingIpv6 is created
  • AddressObserverUsingArp
    • Registers for ARP packet notifications
    • Uses AddressObservationWriter to write address observations from ARP packets
  • AddressObserverUsingIpv4
    • Registers for IPv4 packet notifications
    • Uses AddressObservationWriter to write address observations from IPv4 packets
  • AddressObserverUsingIpv6
    • Registers for IPv6 packet notifications
    • Uses AddressObservationWriter to write address observations from IPv6 packets
  • AddressObservationWriter
    • Writes new Address Observations to the Inventory data tree
    • Updates existing Address Observations with updated “last seen” timestamps
      • Uses the timestamp-update-intervval configuration variable to determine whether or not to update

Configuration

  • timestamp-update-interval
    • A last-seen timestamp is associated with each address. This last-seen timestamp will only be updated after timestamp-update-interval milliseconds.
    • A higher value has the advantage of performing less writes to the database.
    • A lower value has the advantage of knowing how fresh an address is.
  • observe-addresses-from
    • IP and MAC addresses can be observed/learned from ARP, IPv4, and IPv6 packets. Set which packets to make these observations from.

Further development

Further improvements can be made to the AddressObservationWriter so that it (1) doesn’t make any unnecessary writes to the DB and (2) is optimized for multi-threaded environments.

Validating changes to Address Tracker

Address Observations are added to the Inventory data tree.

The Address Observations on a Node Connector can be checked through a browser or a REST Client.

http://10.194.126.91:8080/restconf/operational/opendaylight-inventory:nodes/node/openflow:1/node-connector/openflow:1:1

The Address Observations should still be there after changes.

Developer’s Guide for Host Tracker

Validationg changes to Host Tracker

Host information is added to the Topology data tree.

  • Host address
  • Attachment point (link) to a node/switch

This host information and attachment point information can be checked through a browser or a REST Client.

http://10.194.126.91:8080/restconf/operational/network-topology:network-topology/topology/flow:1/

Host information should still be there after changes.

L2Switch Main

Classes

  • L2SwitchMainModule
    • Reads config subsystem value for is-install-dropall-flow
      • If is-install-dropall-flow is true, then an InitialFlowWriter is created
    • Reads config subsystem value for is-learning-only-mode
      • If is-learning-only-mode is false, then a ReactiveFlowWriter is created
  • InitialFlowWriter
    • Only created when is-install-dropall-flow is true
    • Installs a flow, which drops all packets, on each switch. This flow has low priority and means that packets that don’t match any higher-priority flows will simply be dropped.
  • ReactiveFlowWriter
    • Reacts to network traffic and installs MAC-to-MAC flows on switches. These flows have matches based on MAC source and MAC destination.
    • Uses FlowWriterServiceImpl to write these flows to the switches
  • FlowWriterService / FlowWriterServiceImpl
    • Writes flows to switches

Configuration

  • is-install-dropall-flow
    • “true” means a drop-all flow will be installed on each switch, so the default action will be to drop a packet instead of sending it to the controller
    • “false” means this flow will not be installed
  • dropall-flow-table-id
    • The dropall flow will be installed on the specified flow table of each switch
    • This field is only relevant when “is-install-dropall-flow” is set to “true”
  • dropall-flow-priority
    • The dropall flow will be installed with the specified priority
    • This field is only relevant when “is-install-dropall-flow” is set to “true”
  • dropall-flow-idle-timeout
    • The dropall flow will timeout (removed from the switch) if the flow doesn’t forward a packet for x seconds
    • This field is only relevant when “is-install-dropall-flow” is set to “true”
  • dropall-flow-hard-timeout
    • The dropall flow will timeout (removed from the switch) after x seconds, regardless of how many packets it is forwarding
    • This field is only relevant when “is-install-dropall-flow” is set to “true”
  • is-learning-only-mode
    • “true” means that the L2Switch will only be learning addresses. No additional flows to optimize network traffic will be installed.
    • “false” means that the L2Switch will react to network traffic and install flows on the switches to optimize traffic. Currently, MAC-to-MAC flows are installed.
  • reactive-flow-table-id
    • The reactive flow will be installed on the specified flow table of each switch
    • This field is only relevant when “is-learning-only-mode” is set to “false”
  • reactive-flow-priority
    • The reactive flow will be installed with the specified priority
    • This field is only relevant when “is-learning-only-mode” is set to “false”
  • reactive-flow-idle-timeout
    • The reactive flow will timeout (removed from the switch) if the flow doesn’t forward a packet for x seconds
    • This field is only relevant when “is-learning-only-mode” is set to “false”
  • reactive-flow-hard-timeout
    • The reactive flow will timeout (removed from the switch) after x seconds, regardless of how many packets it is forwarding
    • This field is only relevant when “is-learning-only-mode” is set to “false”

Further development

The ReactiveFlowWriter needs to be improved to install the MAC-to-MAC flows faster. For the first ping, the ARP request and reply are successful. However, then the ping packets are sent out. The first ping packet is dropped sometimes because the MAC-to-MAC flow isn’t installed quickly enough. The second, third, and following ping packets are successful though.

API Reference Documentation

Further documentation can be found by checking out the L2Switch project.

Checking out the L2Switch project

git clone https://git.opendaylight.org/gerrit/p/l2switch.git

The above command will create a directory called “l2switch” with the project.

Testing your changes to the L2Switch project

Running the L2Switch project

To run the base distribution, you can use the following command

./distribution/base/target/distributions-l2switch-base-0.1.0-SNAPSHOT-osgipackage/opendaylight/run.sh

If you need additional resources, you can use these command line arguments:

-Xms1024m -Xmx2048m -XX:PermSize=512m -XX:MaxPermSize=1024m'

To run the karaf distribution, you can use the following command:

./distribution/karaf/target/assembly/bin/karaf

Create a network using mininet

sudo mn --controller=remote,ip=<Controller IP> --topo=linear,3 --switch ovsk,protocols=OpenFlow13
sudo mn --controller=remote,ip=127.0.0.1 --topo=linear,3 --switch ovsk,protocols=OpenFlow13

The above command will create a virtual network consisting of 3 switches. Each switch will connect to the controller located at the specified IP, i.e. 127.0.0.1

sudo mn --controller=remote,ip=127.0.0.1 --mac --topo=linear,3 --switch ovsk,protocols=OpenFlow13

The above command has the “mac” option, which makes it easier to distinguish between Host MAC addresses and Switch MAC addresses.

Generating network traffic using mininet

h1 ping h2

The above command will cause host1 (h1) to ping host2 (h2)

pingall

pingall will cause each host to ping every other host.

Miscellaneous mininet commands

link s1 s2 down

This will bring the link between switch1 (s1) and switch2 (s2) down

link s1 s2 up

This will bring the link between switch1 (s1) and switch2 (s2) up

link s1 h1 down

This will bring the link between switch1 (s1) and host1 (h1) down