Information Technology Reference
In-Depth Information
Foundation Topics
This chapter covers the high-level characteristics of routing protocols and their metrics.
Yo u s h o u l d b e c o m e f a m i l i a r w i t h t h e d i f fe r e n t c a t e g o r i e s o f r o u t i n g p r o t o c o l s a n d t h e i r
characteristics for the exam. Understand how each metric is used and, based on the met-
ric, which path is preferred. For example, you need to know that a path with the highest
bandwidth is preferred over a path with lower bandwidth. This chapter also covers dis-
tance vector routing protocols: RIPv2, RIPng, and EIGRP.
Routing Protocol Characteristics
This section discusses the different types and characteristics of routing protocols.
Characteristics of routing-protocol design are
Distance-vector, link-state, or hybrid: How routes are learned
Key
To p i c
Interior or exterior: For use in private net works or the public Internet
Classless (classless interdomain routing [CIDR] support) or classful: CIDR
enables aggregation of network advertisements (supernetting) between routers
Fixed-length or variable-length subnet masks (VLSM): Conserve addresses
within a network
Flat or hierarchical: Addresses scalability in large internetworks
IPv4 or IPv6: Newer routing protocols are used for IPv6 networks
This section also covers the default administrative distance assigned to routes learned
from each routing protocol or from static assignment. Routes are categorized as statically
(manually) configured or dynamically learned from a routing protocol. The following sec-
tions cover all these characteristics.
Static Versus Dynamic Route Assignment
Static routes are manually configured on a router. They do not react to network outages. The
one exception is when the static route specifies the outbound interface: In this situation, if
the interface goes down, the static route is removed from the routing table. Because static
routes are unidirectional, they must be configured for each outgoing interface the router will
use. The size of today's networks makes it impossible to manually configure and maintain all
the routes in all the routers in a timely manner. Human configuration can involve many mis-
takes. Dynamic routing protocols were created to address these shortcomings. They use al-
gorithms to advertise, learn about, and react to changes in the network topology.
The main benefit of static routing is that a router generates no routing protocol overhead.
Because no routing protocol is enabled, no bandwidth is consumed by route advertise-
ments between network devices. Another benefit of static routing protocols is that they
are easier to configure and troubleshoot than dynamic routing protocols. Static routing is
 
 
 
Search WWH ::




Custom Search