• Supported Platforms
• EX Series

• Related Topics
• For more information on high availability features, see the Junos OS High Availability Configuration Guide at http://www.juniper.net/techpubs/software/junos/index.html.
• Virtual Chassis Overview
• Understanding Virtual Chassis Components
• Understanding Virtual Chassis Configurations and Link Aggregation
• Understanding VRRP on EX Series Switches

High Availability Features for EX Series Switches Overview

VRRP

You can configure the Virtual Router Redundancy Protocol (VRRP) or VRRP for IPv6 on Gigabit Ethernet interfaces, 10-Gigabit Ethernet interfaces, and logical interfaces on EX Series switches. When VRRP is configured, the switches act as virtual routing platforms. VRRP enables hosts on a LAN to make use of redundant routing platforms on that LAN without requiring more than the static configuration of a single default route on the hosts. The VRRP routing platforms share the IP address corresponding to the default route configured on the hosts. At any time, one of the VRRP routing platforms is the master (active) and the others are backups. If the master routing platform fails, one of the backup routing platforms becomes the new master, providing a virtual default routing platform and enabling traffic on the LAN to be routed without relying on a single routing platform. Using VRRP, a backup EX Series switch can take over a failed default switch within a few seconds. This is done with minimum loss of VRRP traffic and without any interaction with the hosts.

For more information on VRRP, see Understanding VRRP on EX Series Switches.

Graceful Protocol Restart

With standard implementations of routing protocols, any service interruption requires an affected switch to recalculate adjacencies with neighboring switches, restore routing table entries, and update other protocol-specific information. An unprotected restart of a switch can result in forwarding delays, route flapping, wait times stemming from protocol reconvergence, and even dropped packets. Graceful protocol restart allows a restarting switch and its neighbors to continue forwarding packets without disrupting network performance. Because neighboring switches assist in the restart (these neighbors are called helper switches), the restarting switch can quickly resume full operation without recalculating algorithms from scratch.

On EX Series switches, graceful protocol restart can be applied to aggregate and static routes and for routing protocols (BGP, IS-IS, OSPF, and RIP).

Graceful protocol restart works similarly for the different routing protocols. The main benefits of graceful protocol restart are uninterrupted packet forwarding and temporary suppression of all routing protocol updates. Graceful protocol restart thus allows a switch to pass through intermediate convergence states that are hidden from the rest of the network. Most graceful restart implementations define two types of switches—the restarting switch and the helper switch. The restarting switch requires rapid restoration of forwarding state information so that it can resume the forwarding of network traffic. The helper switch assists the restarting switch in this process. Individual graceful restart configuration statements typically apply to either the restarting switch or the helper switch.

Redundant Routing Engines

Two to ten EX4200 switches can be interconnected to create a Virtual Chassis configuration that operates as a single network entity. Every Virtual Chassis configuration has a master and a backup. The master acts as the master Routing Engine and the backup acts as the backup Routing Engine. The Routing Engine provides the following functionality:

• Runs various routing protocols
• Provides the forwarding table to the Packet Forwarding Engines (PFEs) in all the member switches of the Virtual Chassis configuration
• Runs other management and control processes for the entire Virtual Chassis configuration

The master Routing Engine, which is in the master of the Virtual Chassis configuration, runs Juniper Networks Junos operating system (Junos OS) in the master role. It receives and transmits routing information, builds and maintains routing tables, communicates with interfaces and Packet Forwarding Engine components of the member switches, and has full control over the Virtual Chassis configuration.

The backup Routing Engine, which is in the backup of the Virtual Chassis configuration, runs Junos OS in the backup role. It stays in sync with the master Routing Engine in terms of protocol states, forwarding tables, and so forth. If the master becomes unavailable, the backup Routing Engine takes over the functions that the master Routing Engine performs.

Graceful Routing Engine Switchover

You can configure graceful Routing Engine switchover (GRES) in a Virtual Chassis configuration, allowing the configuration to switch from the master Routing Engine in the master to the backup Routing Engine in the backup with minimal interruption to network communications. When you configure GRES, the backup Routing Engine automatically synchronizes with the master Routing Engine to preserve kernel state information and forwarding state. Any updates to the master Routing Engine are replicated to the backup Routing Engine as soon as they occur. If the kernel on the master Routing Engine stops operating, the master Routing Engine experiences a hardware failure, or the administrator initiates a manual switchover, mastership switches to the backup Routing Engine.

When the backup Routing Engine assumes mastership in a redundant failover configuration (that is, when graceful Routing Engine switchover is not enabled), the Packet Forwarding Engines initialize their state to boot up state before they connect to the new master Routing Engine. In contrast, in a graceful switchover configuration, the Packet Forwarding Engines do not reinitialize their state, but resynchronize their state with the new master Routing Engine. The interruption to the traffic is minimal.

GRES on EX4200 switches supports software features in Junos OS Release 9.2 or later for EX Series switches.

Virtual Chassis Software Upgrade and Failover Features

EX4200 switches provide these features for increased resiliency in Virtual Chassis configurations:

• Virtual Chassis atomic software upgrade—When you upgrade software in a Virtual Chassis configuration, the upgrade will either succeed or fail on all member switches, preventing the situation in which only some of the Virtual Chassis member switches are upgraded.
• Virtual Chassis fast failover—A hardware-assisted failover mechanism that automatically reroutes traffic and reduces traffic loss in the event of a link failure.
• Virtual Chassis split and merge—If there is a disruption to the Virtual Chassis configuration due to member switches failing or being removed from the configuration, the Virtual Chassis configuration splits into two separate Virtual Chassis.

Link Aggregation

You can combine multiple physical Ethernet ports to form a logical point-to-point link, known as a link aggregation group (LAG) or bundle. A LAG provides more bandwidth than a single Ethernet link can provide. Additionally, link aggregation provides network redundancy by load-balancing traffic across all available links. If one of the links should fail, the system automatically load-balances traffic across all remaining links.

You can select up to eight Ethernet interfaces and include them within a LAG. In an EX4200 Virtual Chassis configuration, the interfaces that form a LAG can be on different members of the Virtual Chassis. See Understanding Virtual Chassis Configurations and Link Aggregation.