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Understanding VRRP

 

For Ethernet, Fast Ethernet, Gigabit Ethernet, 10-Gigabit Ethernet, and logical interfaces, you can configure the Virtual Router Redundancy Protocol (VRRP) or VRRP for IPv6. 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 routing platform, 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 device can take over a failed default device within a few seconds. This is done with minimum VRRP traffic and without any interaction with the hosts. Virtual Router Redundancy Protocol is not supported on management interfaces.

Devices running VRRP dynamically elect master and backup devices. You can also force assignment of master and backup devices using priorities from 1 through 255, with 255 being the highest priority. In VRRP operation, the default master device sends advertisements to backup devices at regular intervals. The default interval is 1 second. If a backup device does not receive an advertisement for a set period, the backup device with the next highest priority takes over as master and begins forwarding packets.

Note

Priority 255 cannot be set for routed VLAN interfaces (RVIs).

Note

To minimize network traffic, VRRP is designed in such a way that only the device that is acting as the master sends out VRRP advertisements at any given point in time. The backup devices do not send any advertisement until and unless they take over mastership.

VRRP for IPv6 provides a much faster switchover to an alternate default router than IPv6 neighbor discovery procedures. Typical deployments use only one backup router.

Note

Do not confuse the VRRP master and backup routing platforms with the master and backup member switches of a Virtual Chassis configuration. The master and backup members of a Virtual Chassis configuration compose a single host. In a VRRP topology, one host operates as the master routing platform and another operates as the backup routing platform, as shown in Figure 3.

VRRP is defined in RFC 3768, Virtual Router Redundancy Protocol. VRRP for IPv6 is defined in draft-ietf-vrrp-ipv6-spec-08.txt, Virtual Router Redundancy Protocol for IPv6. See also draft-ietf-vrrp-unified-mib-06.txt, Definitions of Managed Objects for the VRRP over IPv4 and IPv6.

Note

Even though VRRP, as defined in RFC 3768, does not support authentication, the Junos OS implementation of VRRP supports authentication as defined in RFC 2338. This support is achieved through the backward compatibility options in RFC 3768.

Note

On EX2300 and EX3400 switches, the VRRP protocol must be configured with a Hello interval of 2 seconds or more with dead interval not less than 6 seconds to prevent flaps during CPU intensive operations events such as routing engine switchover, interface flaps, and exhaustive data collection from the packet forwarding engine.

Figure 1 illustrates a basic VRRP topology. In this example, Routers A, B, and C are running VRRP and together make up a virtual router. The IP address of this virtual router is 10.10.0.1 (the same address as the physical interface of Router A).

Figure 1: Basic VRRP
Basic VRRP

Because the virtual router uses the IP address of the physical interface of Router A, Router A is the master VRRP router, while routers B and C function as backup VRRP routers. Clients 1 through 3 are configured with the default gateway IP address of 10.10.0.1. As the master router, Router A forwards packets sent to its IP address. If the master virtual router fails, the router configured with the higher priority becomes the master virtual router and provides uninterrupted service for the LAN hosts. When Router A recovers, it becomes the master virtual router again.

Note

In some cases, during an inherit session, there is a small time frame during which two routers are in Master-Master state. In such cases, the VRRP groups that inherit the state do send out VRRP advertisements every 120 seconds. So, it takes the routers up to 120 seconds to recover after moving to Master-Backup state from Master-Master state.

ACX series routers can support up to 64 VRRP group entries. These can be a combination of IPv4 or IPv6 families. If either of the family (IPv4 or IPv6) is solely configured for VRRP, then 64 unique VRRP group identifiers are supported. If both IPv4 and IPv6 families share the same VRRP group, then only 32 unique VRRP identifiers are supported.

Note

ACX Series routers support VRRP version 3 for IPv6 addresses.

ACX5448 router supports RFC 3798 VRRP version 2 and RFC 5798 VRRP version 3. ACX5448 router also supports configuring VRRP over aggregated Ethernet and integrated routing and bridging (IRB) interfaces.

The following limitations apply while configuring VRRP on ACX5448 router:

  • Configure a maximum of 16 VRRP groups.

  • Interworking of VRRP version 2 and VRRP version 3 is not supported.

  • VRRP delegate processing is not supported.

  • VRRP version 2 authentication is not supported.

Figure 1 illustrates a basic VRRP topology with EX Series switches. In this example, Switches A, B, and C are running VRRP and together they make up a virtual routing platform. The IP address of this virtual routing platform is 10.10.0.1 (the same address as the physical interface of Switch A).

Figure 2: Basic VRRP on EX Series Switches
Basic VRRP on EX Series
Switches

Figure 3 illustrates a basic VRRP topology using Virtual Chassis configurations. Switch A, Switch B, and Switch C are each composed of multiple interconnected Juniper Networks EX4200 Ethernet Switches. Each Virtual Chassis configuration operates as a single switch, which is running VRRP, and together they make up a virtual routing platform. The IP address of this virtual routing platform is 10.10.0.1 (the same address as the physical interface of Switch A).

Figure 3: VRRP on Virtual Chassis Switches
VRRP on Virtual Chassis
Switches

Because the virtual routing platform uses the IP address of the physical interface of Switch A, Switch A is the master VRRP routing platform, while Switch B and Switch C function as backup VRRP routing platforms. Clients 1 through 3 are configured with the default gateway IP address of 10.10.0.1 as the master router, Switch A, forwards packets sent to its IP address. If the master routing platform fails, the switch configured with the higher priority becomes the master virtual routing platform and provides uninterrupted service for the LAN hosts. When Switch A recovers, it becomes the master virtual routing platform again.