It may be preferable to run in individual VR mode until VR count exceeds its maximum limit (511 instances), as it gives more flexibility with respect to topology choices and ‘per-VLAN routing control for the same VRID‘. It will allow the VRs configured in different VLANs configured with same VRID to be in different routing states (for example, one VR can be master and that VLAN can do routing, but the other VR can be backup and that VLAN can do Layer 2 forwarding towards the master).
When you try to configure and enable a VR beyond 511 VRs, you are notified to configure VRRP groups and add VRs to appropriate groups. VRs configured on VLANs following the same topology can be grouped together. There can be multiple groups for the same topology for administrative reasons, or for running with different VRRP configurations (like advertisement interval, etc.), or with different Fabric Routing mode.
Alternatively, groups can be configured beforehand and kept for future use. Similarly, VRs can be added to the group beforehand. The groups can be kept in a disabled state (disable vrrp group group_name {configuration | members}) until you are notified to configure VRRP groups (VR count exceeds 511). When groups are in the disabled state, the VRs present in the group configuration run in individual VR mode.
During switchover, it is recommended to execute the commands:
disable vrrp
disable vrrp group group_name members
After adding VRs to group, and enabling group configuration, execute the commands:
enable vrrp
enable vrrp group group_name members
Keeping VRs in disabled state during transition, and then enabling afterwards, ensures that the bulk transfer of VR information across the system occurs more easily.
You can switch to individual VR mode from high-scale mode by disabling all VRRP groups. Since the limit of VRs in individual mode is 511, ensure that greater than 511 VRs are not enabled before disabling the group configuration.
When a group is already operational (the group is enabled, and also its member VRs are enabled), additional VR can be added to the group. It is recommended to disable the VR before adding it to a group that is currently running and forwarding traffic. Enable the VR after it is added to group in all participating routers. This avoids traffic loss during the transition to group mode.
You can have few individual VRs outside of groups. If you are transitioning to high-scale mode when an individual VR is present, disable all VRs (disable vrrp) before the transition and enable all VRs (enable vrrp) after the transition.
For a list of all VRRP group commands, see Configuring VRRP Groups.
Note
If a large number of VRs are added under the same group, the advertisement interval of the primary VR of the group should be increased to multiples of seconds. This reduces the processing load on the VRRP backup router and avoids protocol flaps. For a large IPv6 group, chose an advertisement interval of a greater value than the value of a similarly sized IPv4 group.