07/27/18

datagram = IP addresses + data
- doesn't include MAC addresses
MAC Address vs. IP address
- PC 1 wants to send something to PC 2 - Here is part of what happens
  - can have many routers between the two PC's
  - each router changes MAC address, but not datagram
Routing tables always match to the longest
- Looks at prefixes
Routing Protocols
- Open Shortest Path First (OSPF) is a nonproprietary link-state routing protocol
  - It is a link-state routing protocol
  - Open statndard routing protocol described in RFC 2328
  - Uses the SPF algorithm to calculate the lowest cost to a destination
  - Routing updates are flooded as topology changes occur
- Border Gateway Protocol (BGF) is an exterior routing protocol
  - It is a path vector exterior routing system
  - Goal: enable business relationships
  - Opts for: flexibility scalability
  - But: Performance optimization is secondary
Autonomous Systems (AS)
- Customer - Provider
  - customer pays provider for service
  - the customer is always right
- Thousands of AS's
- complicated relationships
- Multiple providers for one AS
  - multihoming
- Traffic engineering
  - I want to use multiple paths and load balance
Layer 4: Ports
- Transport
- a number that corresponds to
- e.g. :80 = webpage
- TCP and UDP
Payload
- Our data gets more envelopes at lower layers
Same IP address can still have different ports
- e.g. different Google searches

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