Lesson 9 : Intra-AS and Inter-AS Routing

SDN Control Plane

(Software Defined-Network) network-wide logic that controls packet forwarding among a network's SDN-enabled devices and configuration/management of these devices and their services.

SDN controller functionalities (3 layers)

- Communication Layer - Network-wide state-management layer - Interface to network-control application layer

What are the four key characteristics of SDN architecture?

1) Flow based forwarding 2) Separation of data plane and control plane 3) Network control functions: external to data-plane switches 4) a programmable network

SDN control plane divides into what two components?

1) SDN controller 2) SDN network-control applications

Autonomous System (AS)

A group of routers that is under a single administrative authority. - also called domain - Organizing routers (ISP) - An AS is identified by their number (ASN) - Routers with same AS run same routing algorithm and have info about each other.

Management Information Base (MIB)

A virtual database included in an SNMP-compliant device, containing information about configuration and state of the device that can be queried by the SNMP management station.

SNMP (Simple Network Management Protocol) Sec 5.7.2

An Application-layer protocol used to exchange information between network devices. -request/response mode: server sends request to SNMP agent, then agent receives/performs action, and sends reply to the request.

AS-PATH

BGP attribute that contains the list of autonomous systems (AS) that the advertisement has passed. -AS adds its ASN (autonomous system number) to existing list in the AS-PATH.

NEXT-HOP

BGP, provides link between inter-AS and intra-AS routing protocols. - NEXT-HOP is IP address of the router interface that begins the AS-PATH.

External BGP (eBGP)

External BGP (eBGP) is used by BGP to route information between two autonomous systems.

Internal BGP (iBGP)

Internal BGP (iBGP) is used by BGP to exchange information in the autonomous system (AS).

managed device

Networking devices, such as routers and advanced switches, that must be configured to use.

Why do we have different intra-AS and inter-AS routing?

Policy: Admin wants to control how the traffic routes Scale: Save table size in forwarding table Performance: Intra-AS focuses on performance, while inter-AS enforces policies

Intra-autonomous System Routing Protocol

The forwarding/routing algorithm running within same autonomous system (AS) -aka Interior Gateway Protocol (IGP)

Data Plane

The plane on a networking device such as a router or switch that carries user traffic. Also known as the forwarding plane.

Control Plane

The process of decision making, such as routing, blocking, and forwarding, that is performed by protocols. -the brain of the network -SDN manages how network behaves -focus on forwarding only

BGP Attributes

When a router advertises a prefix across a BGP connection, it includes BGP attributes: AS-PATH NEXT-HOP

Inter-autonomous system routing protocol

When routing a packet between a source and destination across multiple AS's.

Route

a prefix along with attributes is called a route in BGP (Border Gateway Protocol). three components NEXT-HOP; AS-PATH; destination

Gateway Router

a router that directly connects to one or more routers in other AS's (router conneted to your local ISP). (advertising reachability)

Interface to Network-control app layer

allows network-controlled apps to read/write network state and flow tables within state management layer. - Northbound interface - controller interacts with network apps - RESTful API, Network graph,

Network forwarding devices

also known as packet switches

SDN Controller - Network -wide State-management layer

configuring flow tables in all switches to achieve the desired end-end forwarding, require controller to have updated network info of SDN controlled devices. - control decisions made by the SDN Controller - Stats, flow tables - link-state info, host info, switch info

Internal Router

connects only to hosts and routers within its own AS.

ICMP messages

contains header and first 8 bytes of IP datagram

managing server

controls collection, processing, analysis, and display network management info. -control network behavior

Network Management Sec 5.7

includes the deployment, integration, and coordination of hardware, software, and human elements to monitor, test, configure, and control the network.

SDN Controller - Communication Layer

is the lowest layer of controller architecture. - communication between controller and controlled device aka Southbound interface. - OpenFlow - SNMP

ICMP (Internet Control Message Protocol) Sec. 5.6

is used by hosts and routers to communicate network-layer info to each other. -error reporting (destination network unreachable)

OSPF (Open Shortest Path First)

most commonly used intra-AS protocol -uses link state algorithm (Dijkstra's) and broadcast all info to routers. - all messages are authenticated

OpenFlow Protocol

operates between SDN controller and an SDN controlled switch, or a device implementing OpenFlow API. - operates over TCP, port# 6653

network management protocol

protocol between managing server and devices. - allows network admin to manage network

hot potato routing

route chosen with least cost to the NEXT-HOP router beginning that route. -selects route with smallest of the least-cost paths

Border Gateway Protocol (BGP)

standard inter-AS routing protocol that supports the exchange of routing information between autonomous networks. -allows subnets to advertise on internet -determines best routes to prefixes