Chapter 7. Availability and Redundancy

Terms you'll need to understand:

• Route Processor Redundancy (RPR) and RPR+

• Proxy ARP and ICMP Router Discover Protocol (IRDP)

• Hot Standby Routing Protocol (HSRP)

• Virtual Router Redundancy Protocol (VRRP)

Techniques you'll need to master:

• Knowing the similarities and differences between RPR and RPR+

• Using uplink interfaces for redundant switch connections

• Understanding the different methods of default gateway redundancy

• Knowing the HSRP components, its operation, and configuration

• Understanding the components and operation of VRRP

As you deploy more and more critical services in your network, redundancy and availability become key issues. There are many types of availability and redundancy. This chapter focuses on three: hardware, Layer 2, and Layer 3.

With hardware redundancy, you're concerned with the reliability of your hardware components within a chassis. For example, if your networking device has only one power supply, and it fails, the network device would fail. Depending on your product, you might have several choices of hardware redundancy options: redundant power supplies, redundant supervisor engines, redundant RP cards, and redundant line cards. The first section of this chapter focuses on Cisco solutions for hardware redundancy.

In Layer 2 redundancy, you're concerned about either switching paths or switches in your network failing. This could be problematic if you have only a single path to use between two devices. The second part of this chapter focuses on Layer 2 redundancy solutions.

Recall from Chapter 2, "Designing Switched Networks," that traffic that needs to leave a switch block travels through the distribution layer, where an RP handles the path decisions. The use of a router at the distribution layer contains many networking problems and issues. If you have only a single RP and it fails, networking resources in other parts of the network will not be reachable. Layer 3 redundancy can be accomplished in many ways. Your end stations could use IRDP or Proxy ARP, or they could run a routing protocol that is compatible with the RP distribution devices. However, each of these possibilities presents its own set of problems. Cisco's Hot Standby Routing Protocol (HSRP) solves these problems. It provides a backup solution for default gateways that is transparent to the end stations. Other solutions include the Virtual Router Redundancy Protocol (VRRP), Gateway Load Balancing Protocol (GLBP), Single Router Mode (SRM), and Server Load Balancing (SLB). The third, and most important part of this chapter focuses on these Layer 3 redundancy and availability solutions.