CCNA 200-301 Day 25 Study Notes: RIP & EIGRP

Exam Overview

The content presented here outlines the general guidelines for the subjects likely to appear on the CCNA 200-301 exam. It should be noted that other related topics may also appear in a specific delivery of the exam, and these guidelines may be altered without prior notice.

Topics Covered

  • Routing Information Protocol (RIP)

  • Enhanced Interior Gateway Routing Protocol (EIGRP)

Routing Information Protocol (RIP)

RIP, or Routing Information Protocol, is an industry standard distance vector interior gateway protocol (IGP).

Characteristics of RIP

  • Distance Vector IGP: Utilizes routing-by-rumor logic to learn and share routes.

  • Metric: Utilizes hop count; one router constitutes one hop, meaning bandwidth is irrelevant.

  • Maximum Hop Count: The maximum number of hops is 15; any routes exceeding this hop count are deemed unreachable.

Versions of RIP

RIP comprises three versions:

  1. RIPv1:

    • Only advertises classful addresses (Class A, Class B, Class C).

    • Does not support Variable Length Subnet Masking (VLSM) or Classless Inter-Domain Routing (CIDR).

    • Lacks subnet mask information in advertisements. For example:

      • 10.1.1.0/24 would be advertised as 10.0.0.0 (assumed to be /8).

      • 172.16.192.0/18 would be advertised as 172.16.0.0 (assumed to be /16).

      • 192.168.1.4/30 would be advertised as 192.168.1.0 (assumed to be /24).

    • Broadcast messages to 255.255.255.255.

  2. RIPv2:

    • Supports VLSM and CIDR.

    • Includes subnet mask information in advertisements.

    • Messages are multicast to the address 224.0.0.9.

      • Broadcast messages reach all devices on the local network, while multicast messages specifically engage devices that have joined that multicast group.

  3. RIPng (RIP Next Generation):

    • Utilized for IPv6 networks.

RIP Message Types

RIP uses two primary message types for its operations:

  • Request: This message requests that RIP-enabled neighbor routers share their routing tables.

  • Response: This message is used to send the local router’s routing table to its neighboring routers.

Default Behavior

RIP-enabled routers will share their routing tables every 30 seconds by default.

Configuration of RIP

When configuring RIP, routers must utilize the 'network' command to specify which networks should be included in RIP broadcasts.

Example Network Configuration

Consider the following configurations:

  • Router Interfaces: R1, R3, R4, R2 have specific IP addresses configured as follows:

    • R1 Interfaces: 10.0.12.0/30, 10.0.13.0/30, 10.0.24.0/30

    • G0/0 Subnet: 192.168.4.0/24

Network Command Functionality

The network command performs several key functions:

  • Tells the router to look for interfaces with IP addresses within the specified range.

  • Activates RIP on the interfaces that fall under the specified range.

  • Forms adjacencies with connected RIP neighbors in that range.

  • Advertises the network prefix of the interface, not the prefix specified in the network command itself.

Example of Classful Activation

When using a classful approach, a command like network 10.0.12.0 will be interpreted as network 10.0.0.0, meaning the router will activate RIP on any interfaces that fall within that classful range.

  • For instance, both 10.0.12.1 and 10.0.13.1 match the /8 range of 10.0.0.0, thus RIP is activated on G0/0 and G1/0. R1 will then advertise 10.0.12.0/30 and 10.0.13.0/30.

Passive Interface Feature

The passive-interface command instructs a router to cease sending RIP advertisements out of the designated interface while still maintaining the ability to advertise the network prefix of the interface to its RIP neighbors. This command should be applied to interfaces that do not possess RIP neighbors to minimize unnecessary traffic and processing overhead.

Default Route Advertisement in RIP

In scenarios where R1 has a default route leading to the internet, it may be necessary to advertise this route to R2. This is achievable by using the command:

  • default-information originate

The Default-Information Originate Command

This command allows the router to distribute its default route to its RIP neighbors, ensuring that connected networks receive this routing information.

Enhanced Interior Gateway Routing Protocol (EIGRP)

EIGRP, or Enhanced Interior Gateway Routing Protocol, evolved from Cisco's proprietary routing systems and is now an open standard, allowing other hardware vendors to utilize it.

Characteristics of EIGRP

  • Considered an advanced or hybrid distance vector routing protocol.

  • Offers significantly faster convergence than RIP when network changes occur, elaborating the instance of network reliability.

  • Unlike RIP, EIGRP does not impose the 15-hop limit, allowing for larger networks.

  • Uses a multicast address, specifically 224.0.0.10, for route updates.

  • Notable for its ability to perform unequal-cost load balancing, a flexibility that further distinguishes it from RIP which does equal-cost multi-path (ECMP) routing by default.

EIGRP Configuration

When configuring EIGRP, routers must match the Autonomous System (AS) number; otherwise, adjacency formation cannot occur.

  • The network command in EIGRP utilizes wildcard masks in place of standard subnet masks, providing an efficient way to specify routing updates (explained further in forthcoming sections).

Wildcard Masks

Wildcard masks serve as inversions of subnet masks where:

  • 1s in the wildcard mask imply that the corresponding bits need not match.

  • 0s imply that the bits must match.

Determining Wildcard Masks

A shortcut to regenerate a wildcard mask is to subtract each octet of the subnet mask from 255.

Example Calculation

For instance, if the subnet mask is 255.255.248.0, the corresponding wildcard mask would be calculated as follows:

  • 255 - 255 = 0

  • 255 - 255 = 0

  • 255 - 248 = 7

  • 255 - 0 = 255
    Thus, the wildcard mask would be 0.0.7.255.

Understanding EIGRP Network Command

When configuring EIGRP, the network command specifies which interfaces should listen for updates from other devices based on the wildcard masks. A match allows for EIGRP routing protocols to be activated on respective interfaces.

Router ID Determination

The Router ID in EIGRP is thus prioritized in the following order:

  1. Manual configuration

  2. Highest IP address on a loopback interface

  3. Highest IP address on a physical interface

Key Exam Questions

Quiz 1: Default Route Advertisement

Both R1 and R2 utilize RIP to exchange routing information. Given R1's default route to the Internet, which command should be executed?

  • a) R1(config-router)# default-information originate

  • b) R1(config-router)# network 203.0.113.0

  • c) R2(config)# ip route 0.0.0.0 0.0.0.0 10.0.12.1

  • d) R2(config-router)# default-information originate

Quiz 2: Activating EIGRP

R1’s G1/0 interface holds an IP of 172.20.20.17 and the G2/0 interface holds 172.26.20.12. What network command will activate EIGRP on both interfaces?

  • a) R1(config-router)# network 128.0.0.0 127.255.255.255

  • b) R1(config-router)# network 172.16.0.0 0.0.255.255

  • c) R1(config-router)# network 172.20.0.0 0.0.127.255

  • d) R1(config-router)# network 172.20.0.0 0.3.255.255

Quiz 3: EIGRP Router ID Ordering

What is the correct prioritization for determining the EIGRP router ID?

  • a) Highest loopback interface address, then highest physical interface address, then manual configuration.

  • b) Highest physical interface address, then highest loopback interface address, then manual configuration.

  • c) Manual configuration, then highest physical interface address, then highest loopback interface address.

  • d) Manual configuration, then highest loopback interface address, then highest physical interface address.