Saturday, May 12, 2012

Setting Up a CCIE Switching Lab


Layer 2 Ethernet switching is a very important part of a network engineer's job and is a critical component to successfully passing the CCIE written and practical exams. Setting up a switching lab is different from setting up a routing lab because switches cannot be effectively emulated in GNS3/Dynamips. In order to work with a switch IOS, the physical hardware is required because of the specialized ASICs involved. Some switch features can be configured on the Ethernet switching modules available on specific platforms.

The CCIE Routing and Switching exam uses Cisco 3560 switches running a 12.2 IP Services IOS release. In lieu of having access to one or more 3560s, Catalyst 3750 switches are a reasonable substitute and support many of the same features in a similar way. The Cisco 2960 platform is unsuitable for CCIE preparation because the universal image that is used does not support routing. Chassis based switches (4500 and 6500) can also be used, but in many cases the features supported are different from the standalone models.

So, now that we know more about the models that are suitable for preparation, two questions arise: "How many?" and "How should I connect them?" The answer lies in one of the subtleties of the CCIE exam. The goal of the exam is to develop an "internetwork model" according to a set of specifications. The goal of an internetwork model is to develop a scaled-down representation of a complex enterprise network. This gives rise to a lot of the patterns presented in Cisco's Service Oriented Network Architecture (SONA) and the traditional "core-distribution-access" approach. When dealing with these models, there are a couple of useful reference topologies, what I call the "3-switch topology," "core-distribution topology," and "distribution-access topology."

The simple 3-switch topology is a good starting pattern for learning spanning-tree protocol (STP) concepts and how the different forms of STP (STP, Multiple STP [MSTP], and Rapid STP [RSTP]) work together. Generalizing from a 3 switch model to a more complex topology is extremely simple once an individual understands the port roles and transitions that can occur in each type of STP. Utilizing multiple connections between the switches can also demonstrate port aggregation and link-level fault tolerance concepts.

The distribution-access topology provides a fault tolerant layout for many access scenarios. Each of the access layer switches (located at the bottom of the topology) have redundant connections to the distribution layer switches (the top two), a lot of scenarios involving access-layer routing and first-hop redundancy protocols (FHRP) can be demonstrated. Effective demonstrations of the PortFast and UplinkFast features are also possible using this topology.

The distribution-core topology can be used to work with a 4 switch core or redundant connections between the distribution and core layers of an area of the network. This topology can be configured to effectively demonstrate the UplinkFast and BackboneFast features of the switch IOS.

Additional topologies can be created to show activity in specific scenarios, but variations on the above topologies are all that is needed to demonstrate the configuration and behavior of most of the IOS switch features tested on the Cisco certification exams (CCNA, CCNP, and CCIE).

See Also,
The Road to the CCIE

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