You have been introduced to a number of IP routing concepts and have seen how they relate to static, default, and dynamic routing.
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The routing function requires routers to maintain routing tables. Routing knowledge can be entered into a routing table as static, default, or dynamic routes.

A static route is manually defined as the only path 
to a destination.

A default route is the path to take when no route to the destination is known.

Dynamic routes are automatically entered into a routing table. A dynamic routing algorithm is used 
to analyze incoming routing update messages in real time.

The advantage of dynamic routing over static 
routing is its ability to adapt to topology change.

Internetworks can consist of one or more autonomous systems (ASs).

Interior routing protocols are designed to operate within a single AS. Examples of these include:

^B«»^b Routing Information Protocol (RIP)

^B«»^b Interior Gateway Routing Protocol (IGRP)

^B«»^b Open Shortest Path First (OSPF)

^B«»^b Enhanced IGRP

Exterior routing protocols are specifically designed 
to communicate between Autonomous Systems.

Examples of these include:

^B«»^b Exterior Gateway Protocol (EGP)

^B«»^b Border Gateway Protocol (BGP)
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You have looked at distance vector and link-state protocols and seen how to address scalability concerns.
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A scalable routing protocol should:

^B«»^b minimize update traffic

^B«»^b enable rapid convergence

Distance vector protocols have a simple configuration.

In distance vector routing, routing algorithms periodically send complete routing table updates from one router to the next.

The ability of any routing algorithm to select the optimal route depends on the metrics used in the calculation.

Some of the possible metrics are hop count and delay.

Distance vector's slow convergence results
in routing loops or the count to infinity problem.

The count to infinity problem can be avoided by
using holddowns, poison reverse, split horizons, or assigning infinite cost to a route.

Link-state protocols use

^B«»^b link-state packets (LSPs)

^B«»^b topological databases

^B«»^b shortest path first (SPF) algorithms

^B«»^b SPF trees

^B«»^b routing tables

Link-state routers send updates on the state of their own links to all routers in the area simultaneously.

Link-state routing has the advantage of fast convergence. In terms of scalability, link-state protocols have the following problems:

^B«»^b heavy memory, processing and bandwidth
     requirements

^B«»^b unsynchronized updates and segmentation

Link-state protocols have several sophisticated techniques to address resource and coordination problems.

These techniques are:

^B«»^b dampening LSP distribution frequency

^B«»^b creating multicast groups

^B«»^b setting up area hierarchies

^B«»^b time stamps

^B«»^b sequence numbers

^B«»^b aging schemes
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You have learned about route summarization and compared classful, classless, and prefix routing summarization procedures.
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Route summarization is a way of condensing
multiple IP address routing table entries.

Multiple IP addresses must share the same high order bits, and prefix length needs to be indicated
to routers.

Classful routing protocols such as RIP and IGRP do not use effective methods of route summarization.

With both classless and prefix routing, one routing entry can represent a block of host, subnet, or network addresses.

This has the following advantages:

^B«»^b routing tables can be much shorter

^B«»^b switching performance can be faster

^B«»^b routing protocol traffic is reduced

Prefix routing supports discontiguous subnets and mobile hosts.

Enhanced IGRP and OSPF support prefix routing.
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