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Questions and Answers
In a Software Defined Networking (SDN) model, each router independently calculates its own forwarding tables.
False
Routing protocols such as RIP and OSPF are part of the proprietary router operating system.
True
The control plane of a network is traditionally implemented using a centralized approach.
False
BGP is an example of a routing protocol used for routing among ISPs.
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Middleboxes in networking serve a singular purpose within the network layer.
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Centralized programming of routers makes routing tables more difficult to compute.
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Distributed programming eliminates the need for algorithms in each router.
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OpenFlow API allows for easier traffic flow management in networks.
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Link weights are the only mechanism through which control is exerted in traditional routing.
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In traditional routing, it is possible to split traffic among multiple paths for load balancing without any new algorithms.
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The transition from mainframe to PC in SDN is characterized by vertical integration and closed systems.
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Traffic engineering in traditional routing is less flexible due to limited control mechanisms.
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It is possible to define separate routing paths for different types of traffic in traditional routing.
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Destination-based forwarding is the only routing method used in Software Defined Networking (SDN).
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In SDN, data plane switches are typically complex devices that implement specialized forwarding techniques.
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OpenFlow is used to define what is controllable within SDN systems.
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The OpenFlow protocol operates using UDP messages exclusively.
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Controller-to-switch messages include modify-state, which allows the controller to change flow entries.
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Network-control applications in SDN are tightly coupled with the SDN controller.
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Packet-in messages allow the transfer of packets from the switch to the controller.
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SDN network operators directly program switches by creating OpenFlow messages.
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The Internet Control Message Protocol (ICMP) operates at the network layer below IP.
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ICMP messages can be identified by their combination of type and code.
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The SDN approach guarantees improved robustness to failure through a fully decentralized control plane.
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Echo request and reply messages in ICMP can be used for network connectivity checks, such as with ping.
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In SDN, the controller computes congestion levels based on sender rates reported by routers.
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ICMP messages can include the name and IP address of the router when a datagram's TTL expires.
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NETCONF operates using a command line interface only, without any XML format.
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The Simple Network Management Protocol (SNMP) uses a single message type to convey all MIB information.
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The Management Information Base (MIB) is a standardized format for expressing configuration data exclusively from Cisco devices.
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YANG is primarily a programming language used to develop networking hardware.
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A network operator can use SNMP to query device data using a predefined Management Information Base (MIB).
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Timestamp requests and replies in IP protocols help to synchronize clocks between machines.
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UDP segments sent to a destination will continue to be sent indefinitely, regardless of whether they arrive or not.
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Atomic-commit actions in NETCONF allow multiple devices to be updated simultaneously with consistency guarantees.
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The structure of Management Information (SMI) serves as a language for defining operational data but does not include configurations.
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Study Notes
Control Plane in SDN
- SDN (Software Defined Networking) reimagines the network control plane, moving away from distributed, per-router control towards a centralized approach.
- Traditional routers have a monolithic architecture, housing both switching hardware and proprietary implementations of internet protocols (IP, RIP, etc.) within a proprietary OS (e.g., Cisco IOS).
- SDN introduces a remote controller that computes and installs forwarding tables in routers, providing a logical central control point.
- SDN offers advantages like easier network management, flexibility in traffic flows, and open, non-proprietary implementation of control plane, fostering innovation.
- SDN addresses limitations of traditional routing for traffic engineering by enabling fine-grained control over traffic flow and routing policies.
SDN Architecture
- Data plane switches in SDN are fast, simple, and commodity-based, offering generalized data-plane forwarding in hardware.
- The SDN controller acts as a network OS, maintaining network state information and interacting with both network control applications (northbound API) and network switches (southbound API).
- Network-control applications are unbundled, allowing third-party development and separation from routing vendors or SDN controllers.
OpenFlow Protocol
- OpenFlow protocol facilitates communication between the controller and switches.
- It uses TCP for message exchange and supports optional encryption.
- OpenFlow messages are categorized into three classes: Controller-to-switch, Asynchronous (switch-to-controller), and Symmetric (misc.).
- It's distinct from the OpenFlow API, which defines generalized forwarding actions.
- Key controller-to-switch messages include:
-
features: Controller requests switch features. -
configure: Controller queries or sets switch configuration parameters. -
modify-state: Add, delete, or modify flow entries in OpenFlow tables. -
packet-out: Controller sends a packet out of a specific switch port. -
read-state: Collect statistics (counters).
-
- Key switch-to-controller messages include:
-
packet-in: Transfers packet (and its controller) to the controller. -
flow-removed: Flow table entry is deleted at the switch. -
port-status: Informs the controller of a port change. -
error: Error message from the switch.
-
SDN Controllers
- Examples of prominent SDN controllers include:
- OpenDayLight (ODL) controller
- ONOS controller
Challenges in SDN
- Hardening the control plane is crucial, requiring dependable, reliable, scalable, and secure distributed systems. This involves:
- Robustness to failure: Employing reliable distributed system theory for the control plane.
- Dependability and security: Integrating these aspects from the initial development stage.
- Internet-scaling: Extending SDN beyond a single autonomous system.
- SDN is a critical element in 5G cellular networks.
SDN and Future of Traditional Network Protocols
- SDN challenges traditional network protocols by centralizing control plane functions, potentially impacting routing and congestion control mechanisms.
Internet Control Message Protocol (ICMP)
- ICMP facilitates communication of network-level information between hosts and routers.
- It's used for:
- Error reporting (unreachable host, network, port, protocol).
- Echo request/reply (used by
ping).
- ICMP operates at the network layer, above IP.
- ICMP messages are carried within IP datagrams.
- An ICMP message comprises type, code, header, and the first 8 bytes of the IP datagram causing the error.
ICMP Messages
- ICMP messages are identified by a combination of type and code.
- Examples of ICMP message types include:
- Destination unreachable
- Time exceeded
- Source quench (not used)
- Bad parameters (redirection)
- Echo Request/Reply (ping)
- Timestamp Request/Reply
ICMP and traceroute
-
tracerouteutilizes ICMP by sending UDP segments with increasing TTL values to a destination host. - Routers along the path, upon receiving a segment with an expired TTL, discard it and send an ICMP "TTL expired" message back to the source.
- By recording the hop counts and corresponding router information,
traceroutetraces the path to the destination.
Network Management & Configuration
- Network management involves monitoring and controlling a large and complex system composed of thousands of interacting hardware and software components.
Components of Network Management
- Network management encompasses:
- Fault management: Detect and troubleshoot issues in the network.
- Performance management: Monitor network performance and optimize resource utilization.
- Security management: Protect the network from unauthorized access and attacks.
- Configuration management: Manage and automate the configuration of network devices.
- Accounting management: Track network usage and billing.
Network Operator Management Approaches
- Command Line Interface (CLI): Network operators interact directly with individual devices using commands or scripts via SSH.
- SNMP/MIB (Simple Network Management Protocol/Management Information Base): Operators use SNMP to query or set device data within a structured MIB (Management Information Base), providing a standardized mechanism for data exchange.
-
NETCONF/YANG: Offers a more abstract, network-wide perspective with a focus on multi-device configuration management:
- YANG: Data modeling language used to define the structure, syntax, and semantics of NETCONF network management data.
- NETCONF: Facilitates communication of YANG-compatible actions and data to/from/among remote devices.
SNMP Protocol
- SNMP uses two primary methods to convey MIB information and commands:
- Get Request: Retrieves data from the managed device.
- Set Request: Modifies data on the managed device.
- SNMP message types include:
- Get Request: Retrieves specific data from the device.
- Get Next Request: Retrieves data in a sequential manner, starting from a specified point.
- Set Request: Modifies data on the device.
- Trap: Asynchronous notification from the device to the management station.
- The SNMP message format includes:
- Version: SNMP protocol version being used.
- Community String: Access control mechanism to authenticate the management station.
- PDU Type: Type of message, such as Get Request or Set Request.
- Variable Bindings: Contains the data being exchanged.
SNMP: Management Information Base (MIB)
- A managed device's operational (and some configuration) data are organized into a device MIB module.
- There are over 400 MIB modules defined in RFCs, along with many vendor-specific MIBs.
- The Structure of Management Information (SMI) provides a data definition language to structure the MIB.
- Example MIB variables for UDP protocol include:
- udpInDatagrams: Number of UDP datagrams received.
- udpNoPorts: Number of UDP datagrams with no matching port.
- udpInErrors: Number of UDP datagrams received with errors.
NETCONF Overview
- NETCONF focuses on actively managing and configuring devices across a network.
- It operates between a managing server and managed network devices.
- Capabilities of NETCONF include:
- Retrieving, setting, modifying, and activating configurations.
- Atomicity-committing actions across multiple devices.
- Querying operational data and statistics.
- Subscribing to notifications from devices.
- NETCONF uses a Remote Procedure Call (RPC) paradigm using XML-encoded messages exchanged over secure, reliable transport protocols (e.g., TCP with TLS).
NETCONF Initialization, Exchange, Close
- NETCONF communication begins with initialization (establishing a secure session), followed by a series of data exchange (RPC messages), and ultimately termination (session closure).
Selected NETCONF Operations
- Key NETCONF operations include:
- get: Retrieves data from the managed device.
- edit: Modifies the configuration of the managed device.
- copy: Copies configuration data between devices.
- lock: Grants exclusive access to the configuration of the device.
- unlock: Revokes the lock on the device configuration.
- get-schema: Retrieves the schema of the device configuration.
- get-capabilities: Retrieves the management capabilities supported by the device.
Sample NETCONF RPC Message
- A typical NETCONF RPC message is structured as XML, containing the operation type, target device, and data to be exchanged.
YANG
- YANG is a data modeling language designed to define the structure, syntax, and semantics of NETCONF network management data.
- Its features include:
- Built-in data types.
- Generation of XML documents describing device capabilities.
- Expression of constraints among data for a valid NETCONF configuration, ensuring correctness and consistency.
YANG Example
- A YANG example might define the structure of a router configuration, including elements like interfaces, protocols, and security settings.
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Description
This quiz explores the concept of the control plane in Software Defined Networking (SDN). It covers the shift from traditional distributed control methods to a centralized control approach, the architecture of SDN, and its benefits regarding traffic management and innovation. Test your understanding of how SDN improves network efficiency and flexibility.
