This chapter covers the following subjects:
- Resolving InterVLAN Routing Issues: This section begins by contrasting Layer 3 switches and routers. Troubleshooting procedures are also compared for these platforms. Lastly, this section discusses two approaches for routing packets using Layer 3 switches: routed ports and Switched Virtual Interfaces (SVIs).
- Router Redundancy Troubleshooting: This section discusses three approaches to providing first-hop router redundancy. Options include: Hot Standby Routing Protocol (HSRP), Virtual Router Redundancy Protocol (VRRP), and Gateway Load Balancing Protocol (GLBP). Troubleshooting strategies are discussed for HSRP with suggestions on how to modify those strategies for troubleshooting VRRP and GLBP.
- Cisco Catalyst Switch Performance Tuning: This section examines the architecture of a Cisco Catalyst switch and points out different architectural components that could become troubleshooting targets. Also, you are presented with a series of show commands used to gather information about different aspects of a switch's performance.
- Trouble Ticket: HSRP: This section presents you with a trouble ticket and an associated topology. You are also given show and debug command output (baseline output and output collected after a reported issue occurred). Based on the information provided, you hypothesize an underlying cause for the reported issue and develop a solution. You can then compare your solution with a suggested solution.
This chapter builds on Chapter 4, "Basic Cisco Catalyst Switch Troubleshooting," by continuing to focus on troubleshooting Cisco Catalyst Switch platforms. Although the term switch might conjure up the image of a Layer 2 device, many modern switches can also route. Specifically, many switches can make forwarding decisions based on Layer 3 information (for example, IP address information). Therefore, this chapter starts by discussing a couple of ways to make a Layer 3 (or multilayer) switch perform routing.
Next, because many Layer 3 switches reside in a wiring closet, these switches might very well act as the default gateway for endpoints (for example, user PCs). Rather than having this switch (or perhaps a router at the distribution layer) become a single point of failure for endpoints relying on the IP address maintained by that switch (or router), you can take advantage of a first-hop redundancy protocol. A first-hop redundancy protocol allows clients to continue to reach their default gateway's IP address, even if the Layer 3 switch or router that had been servicing that IP address becomes available. This chapter contrasts three first-hop redundancy protocols and discusses the troubleshooting of first-hop redundancy.
Often a trouble reported by a user comes in some variation of, "The network is slow." Although such a description is less than insightful, troubleshooters are likely to encounter network performance issues resulting in a poor user experience. This chapter focuses on troubleshooting performance problems that originate from a Cisco Catalyst switch.
Finally, this chapter presents another trouble ticket. This trouble ticket describes a first-hop redundancy protocol not operating as expected. Given a collection of show and debug output, you are challenged to determine the underlying cause of the issue and formulate a solution.
"Do I Know This Already?" Quiz
The "Do I Know This Already?" quiz helps you determine your level of knowledge of this chapter's topics before you begin. Table 5-1 details the major topics discussed in this chapter and their corresponding quiz questions.
Table 5-1. "Do I Know This Already?" Section-to-Question Mapping
Foundation Topics Section
Resolving InterVLAN Routing Issues
Router Redundancy Troubleshooting
Cisco Catalyst Switch Performance Troubleshooting
What are two differences between Layer 3 switches and routers? (Choose two.)
- Layer 3 switches do not maintain a routing table.
- Layer 3 switches usually forward traffic faster than routers.
- Layer 3 switches support more interface types than routers.
- Layer 3 switches usually support fewer features than routers.
What type of special memory is used by Layer 3 switches, and not routers, that supports very rapid route lookups?
What type of interface can be created on a Layer 3 switch to support routing between VLANs on that switch?
What is the default priority for an HSRP interface?
What is the name for the router in a VRRP virtual router group that is actively forwarding traffic on behalf of the virtual router group?
- virtual forwarder
- active virtual gateway
- virtual router master
- active virtual forwarder
Which of the following statements is true concerning GLBP?
- GLBP is a Cisco proprietary first-hop redundancy protocol.
- GLBP allows multiple routers to simultaneously forward traffic for the group of GLBP routers.
- The active virtual forwarder in a GLBP group is responsible for responding to ARP requests with different MAC addresses.
- A GLBP group has multiple active virtual gateways.
Which of the following is a Cisco proprietary first-hop router redundancy protocol?
What are two components of a switch's control plane? (Choose two.)
- Forwarding logic
Which three of the following are situations when a switch's TCAM would punt a packet to the switch's CPU? (Choose the three best answers.)
- OSPF sends a multicast routing update.
- An administrator Telnets to a switch.
- An ACL is applied to a switch port.
- A switch's TCAM has reached capacity.
The output of a show processes cpu command on a switch displays the following in the first line of the output:
CPU utilization for five seconds: 10%/7%; one minute: 12%; five minutes: 6%
Based on the output, what percent of the switch's CPU is being consumed with interrupts?
- 10 percent
- 7 percent
- 12 percent
- 6 percent