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CCDE Study Guide: Enterprise Campus Architecture Design

Chapter Description

In this chapter from CCDE Study Guide, Marwan Al-shawi discusses issues related to enterprise campus architecture design, including hierarchical design models, modularity, access-distribution design model, layer 3 routing design considerations, EIGRP versus link state as a campus IGP, and enterprise campus network virtualization.

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EIGRP Versus Link State as a Campus IGP

As discussed in Chapter 2, each protocol has its own characteristics, especially when applied to different network topologies. For example, Enhanced Interior Gateway Routing Protocol (EIGRP) offers a more flexible, scalable, and easier-to-control design over “hub-and-spoke” topology compared to link state. In addition, although EIGRP is considered more flexible on multitiered network topologies such as three-tier campus architecture, link-state routing protocols have still proven to be powerful, scalable, and reliable protocols in this type of network, especially OSPF, which is one of the most commonly implemented protocols used in campus networks. Furthermore, in large-scale campus networks, if EIGRP is not designed properly with regard to information hiding and EIGRP query scope containment (discussed in Chapter 2), any topology change may lead to a large floods of EIGRP queries. In addition, the network will be more prone to EIGRP stuck-in-active (SIA) impacts, such as a longer time to converge following a failure event and as a SIA timer puts an upper boundary on convergence times.

Consequently, each design has its own requirements, priorities, and constraints; and network designers must evaluate the design scenario and balance between the technical (protocol characteristics) and nontechnical (business priorities, future plans, staff knowledge, and so on) aspects when making design decisions.

Table 3-2 provides a summarized comparison between the two common and primary IGPs (algorithms) used in large-scale hierarchal enterprise campus networks.

Table 3-2 Link State Versus EIGRP in the Campus

Design Consideration

EIGRP (DUAL)

Link State (Dijkstra)

Architecture flexibility

High (natively supports multitier architectures with routes summarization)

High, with limitations (The more tiers the network has, the less flexible the design can be.)

Scalability

High

High

Convergence time (protocol level)*

Fast (ideally with route summarization)

Fast (ideally with topology hiding, route summarization, and timers tuning)

MPLS-TE support

No

Yes

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