Computer Networks

Control Plane

Determines routes and computes forwarding tables

Data Plane

Forwards packets using the forwarding table

Per-router control plane

Each router independently runs routing algorithms

SDN control plane

A centralized controller computes and installs forwarding tables in routers

Routing protocol goal

Determine good paths from source to destination

Good path

Lowest cost, fastest, or least congested path

Link-state routing

Each router knows the entire network topology

Dijkstra’s algorithm

Used in link-state routing to compute least-cost paths

Key idea of distance-vector routing

Routers send their distance estimates to neighbors periodically

Distance vector convergence

Occurs when routers’ distance estimates match actual least cost paths

Count-to-infinity problem

Slow convergence when link cost increases in distance-vector routing

Good news travels fast

Distance-vector routing quickly updates when path cost decreases

Bad news travels slow

Distance-vector routing slowly updates when path cost increases

Link-state information

Full network topology

Distance-vector information

Neighbor distances only

Link-state convergence speed

Faster and more predictable

Distance-vector convergence speed

Slower and may form routing loops

Link-state robustness

Errors affect only one router

Distance-vector robustness

Errors can spread across the network

Autonomous system (AS)

A group of routers under a single administrative control

Intra-AS routing

Routing within the same autonomous system

Inter-AS routing

Routing between different autonomous systems

Gateway router

A router connecting one autonomous system to another

Why hierarchical routing is used

Improves scalability and reduces routing table size

RIP

Distance-vector routing protocol exchanging updates every 30 seconds

OSPF

Link-state routing protocol used within an autonomous system

BGP

Inter-domain routing protocol used between autonomous systems

BGP description

The protocol that holds the Internet together

BGP path vector protocol

Advertises routes as sequences of autonomous systems

SNMP

Protocol used to monitor and manage network devices

MIB (Management Information Base)

Database of network device information

NETCONF

Protocol used to configure network devices remotely

YANG

Data modeling language used with NETCONF

Managed device

Network hardware being monitored or configured

Managing server

System used by administrators to control network devices