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# Overview

VRRP can prevent loss of network connectivity to end hosts if the static default IP gateway fails. By implementing VRRP, you can designate a number of routers as backup routers in the event that the default master router fails. VRRP fully supports Virtual Local Area Networks (VLANs) and stacked VLANs (S-VLANs).

| Note: The term virtual router as defined in Configuring Virtual Routers in JUNOSe System Basics Configuration Guide, is different from what is implied by VRRP. In this chapter, the term virtual router always refers to a VRRP router; that is, a router that has enabled VRRP.

In case of a failure, VRRP dynamically shifts the packet-forwarding responsibility to a backup router. VRRP creates a redundancy scheme which enables hosts to keep a single IP address for the default gateway but maps the IP address to a well-known virtual MAC address. VRRP provides this redundancy without user intervention or additional configuration at the end hosts.

## VRRP Terms

Table 19 provides definitions for the basic VRRP terms used in this chapter.

Table 19: VRRP Definitions

Term | Definition
--- | ---
VRRP router | A router that is running VRRP. It might participate in one or more virtual router IDs (VRIDs). An IP redundancy instance can: Act as a master with associated addresses it owns at an IP interface Act simultaneously as a backup for other routers with additional VRID mappings and priorities for those routers
Master router | The VRRP router that takes the responsibility of forwarding packets sent to the IP addresses associated with the virtual router, and that answers ARP requests for these IP addresses. If the IP address owner is available, it always becomes the master.
Backup router | The VRRP router available to take forwarding responsibility if the current master router fails.
IP address owner | The IP interface–VRID pair instance that has the associated IP addresses as real interface addresses. This router, when up, responds to packets addressed to one of these IP addresses for Internet Control Message Protocol (ICMP) pings or Transmission Control Protocol (TCP) connections. The IP address owner is the primary router.
Primary IP address | An IP address configured as primary from the set of real interface addresses. VRRP advertisements are always sent (by the master router) using the primary IP address as the source of the IP packet.

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