# 19 Understanding OSPF Concepts

## Comparing Dynamic Routing Protocol Features
**Routers add IP routes to their routing tables using three methods:**
- connected routes
- static routes
- routes learned by using dynamic routing protocols

**Routing protocol:** A set of messages, rules, and algorithms used by routers for the overall purpose of learning routes.
This process includes the exchange and analysis of routing information. Each router chooses the best route to each subnet (path selection) and finally places those best routes in its IP routing table. **Examples include RIP, EIGRP, OSPF, and BGP.**

**Routed protocol and routable protocol:** Both terms refer to a protocol that defines a packet structure and logical addressing, allowing routers to forward or route the packets.
Routers forward packets defined by routed and routable protocols. **Examples include IP Version 4 (IPv4) and IP Version 6 (IPv6).**



### Interior and Exterior Routing Protocols


### Comparing IGPs

#### IGP Routing Protocol Algorithms
The term routing protocol algorithm simply refers to the logic and processes **used by different routing protocols to solve the problem of learning all routes, choosing the best route to each subnet, and converging in reaction to changes in the internetwork.**

Three main branches of routing protocol algorithms exist for IGP routing protocols:

**Metrics**
Routing protocols choose the best route to reach a subnet by choosing the route **with the lowest metric.**