Interior Gateway Protocols (IGPs), also called Intra-Domain Routing Protocols (IDRP)
- are dynamic routing protocols used by routers to exchange routing information WITHIN a single Autonomous System
- the whole point of these protocols is to allow forwarding IP packets on the “shortest” path possible based on link cost
Interior Gateway Protocol Types
- Distance Vector - each node talks only to its directly connected neighbors, but it tells them everything it has learned (i.e., distance to all nodes)
- Link State - each node talks to all other nodes, but it tells them only what it knows for sure (i.e., only the state of its directly connected links)
- Hybrid - a combination of the 2 above
2 circumstances under which a node decides to send a routing update to its neighbors:
- periodic - each node automatically sends an update message every so often
- triggered - a node sends an update message whenever there is a change to its routing table. This change can be caused by the node detection of a link failure or upon receiving an update from one of its neighbors
Metrics - Determining Link Cost
- conventional wisdom now holds that dynamically changing metrics are too unstable
- static metrics are the norm
- one common approach to setting metrics is to use a constant multiplied by (1/link bandwidth)
- TODO page 262