Router

Joins two or more networks
Passes packets from one network to another
Can do the following:
- Connect dissimilar networks (LANs and WANs)
- Interpret layer 3 (network layer) and layer 4 (transport layer) addressing
- Determine the best path for data to follow from point A to point B
- Reroute traffic if the path of first choice is down but another path is available
May perform any of the following:
- Filter broadcast transmissions
- Prevent certain types of traffic from getting to a network
- Support local/remote connectivity simultaneously
- Provide high network fault tolerance through redundant components
  - Such as power supplies
- Monitor network traffic and report stats
- Diagnose internal connectivity problems and trigger alarms
Act as a broadcast boundary
- Don't forward broadcast traffic

Routing Table

Routers and routing tables

Database maintaining information about where hosts are located and the most efficient way to reach them
- Routers rely on them to identify which router is the next hop to reach a particular destination host
Contain IP addresses and network masks that identify a network that a host or another router belongs to

Static routing
- Network admins configure a routing table to direct messages along specific paths
Dynamic routing
- Automatically calculated paths between two networks
- Maintains information in a routing table
- Router can detect problems with failed/congested routes and reroutes messages through a different path

Routing protocols
- Used by routers to communicate with each other to determine the best path
Routers rate reliability and priority of a routing protocol's data based on:
- Administrative distance (AD)
  - Number indicating protocol's reliability
- Convergence time
  - Time it takes to recognize a best path in event of a change or outage
- Overhead
  - Burden places on underlying network to support the protocol