ScreenOS Cookbook

Chapter 18. High Availability with NSRP

18.0. Introduction

The NetScreen Redundancy Protocol (NSRP) is a proprietary protocol originally developed by NetScreen Technologies Inc. The goal of NSRP is to ensure that the firewall and virtual private network (VPN) services are available at all times. There are three primary components of NSRP: gateway failover, session synchronization, and failure detection. The first component is relatively straightforward. Much like the Internet Engineering Task Force (IETF) standard protocol, the Virtual Router Redundancy Protocol (VRRP), NSRP provides a virtual Media Access Control (MAC) address and IP address to the network so that hosts and routers can point statically to a gateway IP. In NSRP terms, a virtual interface is known as a Virtual Security Interface (VSI). When a failure condition is detected, the MAC/IP pair for each interface is “migrated” from one device to the other via the use of gratuitous Address Resolution Protocol (ARP) messages. These ARP messages update the switch’s forwarding database so that traffic destined to the virtual MAC is forwarded to the port to which the new “master” is connected. From the network’s point of view, VRRP and NSRP in most cases use identical mechanisms to signal failover to the rest of the network. At this point, the similarities between the two protocols disappear.

Some of the key differentiators between VRRP and NSRP include the following:

• NSRP typically utilizes dedicated links for heartbeat traffic, ...