Network layer: Control plane¶

How to initiate/manage forwarding table?

Traditional / per-router: individual routing algorithm components in each and every router interact

SDN(Software Defined Networking) / logically centralized control: Remote controller computes, installs forwarding tables in routers

• control agent

Routing algorithm/protocol¶

Classification¶

Third way: load-sensitive / load-insensittive

Dijkstra / link state¶

(for node u)

Algorithm complexity: \(O(n^2)\) or \(O(n \log n)\)

Message complexity: \(O(n^2)\) if a broadcast is only \(O(n)\)

Bellman-Ford / Distance Vector¶

Bellman-Ford Equation: \(d_x(y) = \min_v\{c(x,v) + d_v(y)\}\)

can have problem: after link cost change, bad message spread slow(maybe lots of iteration)

Solution: adding Poisoned Reverse

• Tell small little white lie to avoid attempting looping in the network

converge slowly

errors can diffuse in whole network

Intra-ISP routing: OSPF¶

• scale

• administrative autonomy

==> Autonomous systems (ASs)

Open: indicates that the routing protocol specification is publicly available

link-state protocol

Advances:

1. security
2. multiple same-cost paths
3. integrated support for unicast and multicast routing
4. support for hierarchy within a single AS.

Routing among ISPs: BGP¶

glues thousands of ISPs in the Internet together

Basics

Advertisement¶

Messages¶

Hot-potato routing¶

choose local gateway that has least intra-domain cost

Route Selection¶

Router may learn about more than one route to destination AS, selects route based on:

1. local preference value attribute: policy decision
2. shortest AS-PATH
3. closest NEXT-HOP router: hot potato routing
4. additional criteria

SDN control plane¶

Characteristics:

• Flow-based forwarding
• Separation of data plane and control plane
• Network control functions: external to data-plane switches
• Programmable

Logically centralized control plane

• easy management
  • avoid router misconfiguations
  • greater flexibility of traffic flows
• centralize programming is easier
• open implementation of control plane

Solve problems:

• prefer route
• load balancing

Data-plane switches¶

API for table-based switch control (e.g. Openflow)

physical machine

SDN controller(network OS)¶

maintain network state information

interacts with

• network control applications "above" via northbound API

• network switches "below" via southbound API

implemented as distributed system for

• performance
• scalability
• fault-tolerance
• robustness

Network-control apps¶

"brains" of control: implement control functions using lower level services

Problems¶

harden the control plane

internet scaling can be hard

5G cellular networks

OpenFlow¶

Protocol¶

operates between controller and switch, over TCP, default port 6653

three types of messages

• controller-to-switch

  • configuration
  • read-state: query [feature]
  • modify-state: in flow table
  • send-packet

• switch-to-controller (asynchronous)

  • packet-in
  • flow-removed: flow table entry deleted
  • port-status: change in port status

ICMP(Internet Control Message Protocol)¶

Communicate network-level information

network-layer "above" IP

used by trace route

Network management¶

Network management includes:

• deployment

• integration

• coordination

of

• hardware
• software
• human elements

to

• monitor
• test
• poll
• configure
• analyze
• evaluate
• control

the network and element resources to meet:

• real-time
• operational performance
• Quality of Service requirements

at a reasonable cost.

Components¶

CLI:

SNMP/MIB: operator queries/sets devices data(MIB) using SNMP

NETCONF/YANG:

• more abstract, network-wide, holistic

• emphasis on multi-device configuration management

• YANG: Data modeling language
• NETCONF: communicate Yang-compatible actions/data to/from/among remote devices

SNMP¶

Application Layer protocol

convey network-management control and information messages

• request-response mode: get data/return data
• trap mode: inform manager of exceptional event

Message format:

MIB: managed device's operational (and config) data

• Language: SMI(Structure of Management Information)

NETCONF¶

actively manage/configure devices network-wide, operates between managing server and managed network devices

• Actions: retrieve, set, modify, activate configurations
• Atomic-commit actions over multiple devices
• query operational data and statisitics
• subscribe to notifications from devices

RPC paradigm

• messages are encoded in XML
• tunnels are secure, reliable transport (e.g. TLS) protocol

Operations:

Yang¶

data modeling language used to specify structure syntax, semantics of NETCONF network management data