13.1.1 Overview

Gigabit Switch Redundancy Protocol (GSRP) provides redundancy for the Switch by securing a communication path via another switch in the same network even if the primary switch has failed.

In Layer 2, you can use Spanning Tree Protocols to provide redundancy on the network.In Layer 3, you can use VRRP to provide redundancy for the default gateway.However, GSRP can by itself provide redundancy for both Layers 2 and 3.

• Layer 2

  Because the paired switches exchange control frames to check each other's status, the switchover from one switch to another is faster than using a Spanning Tree Protocol. GSRP is also suitable for large-scale configurations in which core switches are used in multiple stages on a network.

• Layer 3

  GSRP provides redundancy for the default gateway by allowing the paired switches to have the same IP addresses and same MAC address. By using GSRP for the default gateway for PCs, you can have redundant communication paths from PCs to the upstream network. If the default gateway device fails, the backup device takes over for the original device by using the same IP addresses and MAC address allowing the PCs to continue sending traffic through the default gateway.

The following table compares the protocols for providing redundancy simultaneously for both Layers 2 and 3.

Table 13-1: Comparison of the functionality that makes Layer 2 and Layer 3 redundant at the same time

Protocol for redundancy	Description
GSRP	Management is easy because one protocol provides redundancy for both Layers 2 and 3. GSRP is specific to the Switch.GSRP switches cannot be connected to switches manufactured by other companies.
Spanning Tree Protocols and VRRP	Both a Spanning Tree Protocol and VRRP must be configured to provide redundancy simultaneously for both Layers 2 and 3. Because these protocols are standards, you can create a network consisting of switches and routers manufactured by different vendors.

The following figure provides an overview of redundancy in Layer 2 provided by GSRP.

Figure 13-1: Introduction to GSRP

The Switches with GSRP are paired to create a group. In normal operation, one switch serves as the master switch and the other serves as the backup switch. The master Switch (Switch A) forwards frames, and the backup Switch (Switch B) blocks frames. If a link or a switch fails, the master/backup relationship between Switches A and B is reversed, allowing communication to continue.