Summary

The main topics covered in this chapter are the following:

• How routers forward traffic through a network based on source and destination IP addresses.

• The sources of route information used to populate a router’s routing table. These sources include directly connected routes, statically configured routes, and dynamically learned routes.

• A distinction was made between routed protocols (for example, IP) and routing protocols (such as OSPF or EIGRP).

• Some routing sources are more trustworthy than other routing sources, based on their administrative distances (AD).

• Different routing protocols use different metrics to select the best route in the presence of multiple routes.

• This chapter distinguished between IGPs (which run within an autonomous system) and EGPs (which run between autonomous systems).

• The behavior of distance-vector and link-state routing protocols were contrasted, and you saw how spilt horizon and poison reverse could prevent a routing loop in a distance-vector routing protocol environment.

• Today’s most popular routing protocols (including RIP, OSPF, IS-IS, EIGRP, and BGP) were presented, along with their characteristics.

• NAT can be used to translate private IP addresses inside a network to publicly routable IP addresses. Additionally, this chapter contrasted variations of NAT: PAT, SNAT, and DNAT.

• This chapter discussed the IGMP and PIM protocols used in multicast networks. These protocols work together to allow a network to only forward multicast traffic over links needing that traffic.