Cisco Networking Academy's Introduction to Routing Dynamically

This chapter explains multiple routing protocols (particularly dynamic routing protocols) and describes their relative strengths and weaknesses. It also shows how to read a routing table easily and interpret the IPv6 routing information listed within it.

From the Book

Types of Distance Vector Routing Protocols (3.2.2)

There are two main distance vector routing protocols. This section highlights similarities and differences between RIP and EIGRP.

Routing Information Protocol (3.2.2.1)

The Routing Information Protocol (RIP) was a first generation routing protocol for IPv4 originally specified in RFC 1058. It is easy to configure, making it a good choice for small networks.

RIPv1 has the following key characteristics:

• Routing updates are broadcasted (255.255.255.255) every 30 seconds.
• The hop count is used as the metric for path selection.
• A hop count greater than 15 hops is deemed infinite (too far). That 15th hop router would not propagate the routing update to the next router.

In 1993, RIPv1 evolved to a classless routing protocol known as RIP version 2 (RIPv2). RIPv2 introduced the following improvements:

• Classless routing protocol: It supports VLSM and CIDR, because it includes the subnet mask in the routing updates.
• Increased efficiency: It forwards updates to multicast address 224.0.0.9, instead of the broadcast address 255.255.255.255.
• Reduced routing entries: It supports manual route summarization on any interface.
• Secure: It supports an authentication mechanism to secure routing table updates between neighbors.

Table 3-5 summarizes the differences between RIPv1 and RIPv2.

Table 3-5 RIPv1 versus RIPv2

Characteristics and Features

RIPv1

RIPv2

Metric

Both use hop count as a simple metric. The maximum number of hops is 15.

Updates Forwarded to Address

Supports VLSM

Supports CIDR

Supports Summarization

Supports Authentication

RIP updates are encapsulated into a UDP segment, with both source and destination port numbers set to UDP port 520.

In 1997, the IPv6-enabled version of RIP was released. RIPng is based on RIPv2. It still has a 15-hop limitation and the administrative distance is 120.

Enhanced Interior Gateway Routing Protocol (3.2.2.2)

The Interior Gateway Routing Protocol (IGRP) was the first proprietary IPv4 routing protocol, developed by Cisco in 1984. It used the following design characteristics:

• Bandwidth, delay, load, and reliability are used to create a composite metric.
• Routing updates are broadcast every 90 seconds, by default.

In 1992, IGRP was replaced by Enhanced IGRP (EIGRP). Like RIPv2, EIGRP also introduced support for VLSM and CIDR. EIGRP increases efficiency, reduces routing updates, and supports secure message exchange.

Table 3-6 summarizes the differences between IGRP and EIGRP.

Table 3-6 IGRP versus EIGRP

Characteristics and Features

IGRP

EIGRP

Metric

Both use a composite metric based on bandwidth and delay. Reliability and load can also be included in the metric calculation if configured.

Updates Forwarded to Address

Supports VLSM

Supports CIDR

Supports Summarization

Supports Authentication

EIGRP also introduced:

• Bounded triggered updates: It does not send periodic updates. Only routing table changes are propagated, whenever a change occurs. This reduces the amount of load the routing protocol places on the network. Bounded triggered updates means that EIGRP only sends to the neighbors that need it. It uses less bandwidth, especially in large networks with many routes.
• Hello keepalive mechanism: A small Hello message is periodically exchanged to maintain adjacencies with neighboring routers. This means a very low usage of network resources during normal operation, instead of the periodic updates.
• Maintains a topology table: Maintains all the routes received from neighbors (not only the best paths) in a topology table. DUAL can insert backup routes into the EIGRP topology table.
• Rapid convergence: In most cases, it is the fastest IGP to converge because it maintains alternate routes, enabling almost instantaneous convergence. If a primary route fails, the router can use the alternate route identified. The switchover to the alternate route is immediate and does not involve interaction with other routers.
• Multiple network layer protocol support: EIGRP uses Protocol Dependent Modules (PDM), which means that it is the only protocol to include support for protocols other than IPv4 and IPv6, such as legacy IPX and AppleTalk.

Activity 3.2.2.3: Compare RIP and EIGRP

Go to the online course to perform this practice activity.

Packet Tracer Activity 3.2.2.4: Comparing RIP and EIGRP Path Selection

PCA and PCB need to communicate. The path that the data takes between these end devices can travel through R1, R2, and R3, or it can travel through R4 and R5. The process by which routers select the best path depends on the routing protocol. We will examine the behavior of two distance vector routing protocols, Enhanced Interior Gateway Routing Protocol (EIGRP) and Routing Information Protocol version 2 (RIPv2).