Improving the Convergence Time for VRRP

You can enable faster convergence time for the configured Virtual Router Redundancy Protocol (VRRP), thereby reducing the traffic restoration time to less than 1 second. To improve the convergence time for the VRRP, perform the following tasks:

• Configure the distributed periodic packet management process—When the VRRP process is busy and does not send VRRP advertisements, the backup VRRP routers might assume that the primary router is down and take over as the primary router, causing unnecessary flaps. To address this problem and to reduce the load on the VRRP process, Junos OS uses the distributed periodic packet management (PPM) process to send VRRP advertisements on behalf of the VRRP process.

  To configure the distributed PPM process, include the delegate-processing statement at the [edit protocols vrrp] hierarchy level.

• Disable the skew timer—The skew timer in VRRP is used to ensure that two backup routers do not switch to the primary state at the same time in case of a failover situation. When there is only one primary router and one backup router in the network deployment, you can disable the skew timer, thereby reducing the time required to transition to the primary state.

  To disable the skew timer, include the skew-timer-disable statement at the [edit protocols vrrp] hierarchy level.

• Configure the number of fast advertisements that can be missed by a backup router before it starts transitioning to the master state—The backup router waits until a certain number of advertisement packets are lost after which it transitions to the primary state. This waiting time can be fatal in scenarios such as router failure or link failure. To avoid such a situation and to enable faster convergence time, in Junos OS Release 12.2 and later, you can configure a fast advertisement interval value that specifies the number of fast advertisements that can be missed by a backup router before it starts transitioning to the primary state.

  To configure the fast advertisement interval, include the global-advertisements-threshold statement at the [edit protocols vrrp] hierarchy level.

• Configure inheritance of VRRP groups—Junos OS enables you to configure VRRP groups on the various subnets of a virtual LAN (VLAN) to inherit the state and configuration of one of the groups, which is known as the active VRRP group. When the vrrp-inherit-from statement is included in the configuration, only the active VRRP group, from which the other VRRP groups inherit the state, sends out frequent VRRP advertisements and processes incoming VRRP advertisements. Use inherit groups for scaled configurations. For example, if you have 1000 VRRP groups with an advertisement interval of 100 ms, then use inherit groups.

  To configure inheritance for a VRRP group, include the vrrp-inherit-from statement at the [edit interfaces interface-name unit logical-unit-number family inet address address vrrp-group group-id] hierarchy level.

• Disable duplicate address detection for IPv6 interfaces—Starting with Junos OS Release 15.1, duplicate address detection is a feature of the Neighbor Discovery Protocol for IPv6. Duplicate address detection is enabled by default and determines whether an address is already in use by another node. When detection address detection is enabled, convergence time is high after an IPv6 interface that has been configured for VRRP tracking comes up. To disable duplicate address detection, include the ipv6-duplicate-addr-detection-transmits 0 statement at the [edit system internet-options] hierarchy level. To disable duplicate address detection only for a specific interface, include the dad-disable statement at the [edit interfaces interface-name unit logical-unit-number family inet6] hierarchy level.