Ex2 Chapter 1 - Introduction to Routing and Packet Forwarding

Static and Dynamic Routing
Routers know of networks that are only directly connected to them.  Obviously, routers need some method of learning about distant networks they need to access.  There are two methods of learning about these distant networks, static and dynamic route learning. Static routes are when an administrator adds specific network routes to a router or multiple routers.

•  Router memory
   o  ROM – Basic operations
   o  RAM – Running-config and IOS
   o  NVRAM – Stores startup-config
   o  Flash – Stores IOS
•  Boot Process
•  Static Routing


Static routes can be problematic at times because they are not easily maintained.  They are also prone to  human errors.  They should be used in only specific circumstances.

When to use static routes:
1.  Network consists of only a few routers.
2.  Network is connected to the Internet through only one ISP.
3.  A large network is configured in a hub-and-spoke topology (star).

When using dynamic routing an administrator must choose an autonomous, system widerouting protocol.  A routing protocol is a service that runs on a router that controls how routers communicate routing table information to each other.  There are multiple protocols available on Cisco routers.  The following is a list of routing protocols:

•  RIP – Routing Information Protocol
•  IGRP – Interior Gateway Routing Protocol
•  EIGRP – Enhanced IGRP
•  OSPF – Open Shortest Path First
•  IS-IS – Intermediate System to Intermediate System 
•  BGP – Border Gateway Protocol
 Dynamic routing is very efficient and aides administrators.  When setting up dynamic routing the administrator usually only needs to inform the specific router of the routes it is directly connected to and only those dc routes it wants broadcasted to other routers.

Three setbacks to dynamic routes that do not exist in static routing are:
1.  Routing loops
2.  Process intensive
3.  Bandwidth consumption through configured updates

Each routing protocol attempts to solve the above setbacks in their own manner.

Equal Cost Load Balancing

Equal cost is when two or more routes exist that are all of equal worth to the router (worth is measured by metrics).  A router can be configured to use all n routes instead of only choosing just 1 route.  The process of using multiple equal cost routes is called load balancing and is very beneficial in large network settings. Unequal cost load balancing also exists in some routing protocols and generally uses some epsilon trigger value to define if two routes should load balance.