1. Routes changes slowly over time
2. Usually manually set by command in router

routes change more quickly

1. periodic update
2. in response to link cost changes
3. Affected by other routers changes and changed itself

1. Each router is responsible for meeting its neighbors and learning their names
   -Sending Hello / Keep-alive messages

2. Each router constructs a packet known as a link state packet (LSP) which contains a list of names of and cost to each of its neighbors
3. The LSP is flooded to all other routers, and each router stores the most recently generated LSP from each other router in the whole network.
4. Each router, now armed with a complete map of the network topology
   -Shortest-path-based route will be used

*If not use shortest-path algorithm, looping will occur

Distance Vector routing Algorithm

1. Each router consider themselves as [Distance 0]
2. Each router saves its own ID and attached links's cost
3. Transmit these data to neighbor routers
4. Form a DV table eventually

1. DV has count to infinity problem - I.E. A dead loop will occur when link cost change suddenly
2. LS: Node may advertise incorrect link cost to other routers and other routers use it to build its own table
3. DV may advertise incorrect path cost
4. LS & DV can be down if just one router in the network not following the rules

1. interconnections of Autonomous Systems (AS)
2. Each of AS undergoes Inter-domain routing

AS

1. There are gateway routers
2. Gateway routers run inter-as routing protocol with other ASes
3. Gateway routers run intra-as routing protocol with other routers in a AS
4. Hierarchical Routing