Network Layer

Virtual circuits: like telephone circuit. A VC has path, VC number (number for each link along path), entries in forwarding tables.

• not used in today's internet.

Datagram networks:

• no setup
• forward using destination host address.
• internet
• simple inside network

Longest prefix match: when looking for forwarding table entry for given address, use longest address prefix that matches destination address

CIDR: classless interdomain routing

• address format: a.b.c.d/x, where x is # bits in subnet portion of address.

A host gets the IP address via DHCP: dynamic host configuration protocol: dynamically gets address from a server

NAT: network address translation: local network uses one IP from the pov of outside.

ICMP: communicate network level info.

ipv6 because needed more bits.

• tunneling: storing ipv6 inside ipv4 packet.

Routing

Routing algorithms can be:

• global vs decentralized.
  • global: all routers have complete info to the topology, and link cost info. "link state algorithms".
  • decentralized: only knows of neighbor

routing models:

• centralized vs decentralized:
• flow based (every packet has flow), aggregated (group)
• reactive (first packet triggers controller to insert) vs proactive (pre populate)

SDN

OpenFlow protocol:

• match fields, actions, stats

The controller has:

• interface layer (api)
• network-wide state management: store state
• communication: communicate between SDN controller and switches