Dell SmartFabric OS10 User Guide Release 10.5.3

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Configuring BFD session tracking under VRRP group

Consider the following topology:

bfd-session-tracking-under-vrrp-group

Following are the configuration steps for topology in the above figure:

OS10A - VRRP Primary configuration

Create a track object and configure a BFD session.

OS10-A(config)# track 1
OS10-A(conf-track-1)#bfd interface vlan 20 vrf default source-ip-address 11.11.11.1 neighbor-ip-address 11.11.11.2 interval 
50 min_rx 50 multiplier 5 role active

Create a VLAN and a VRRP group under the VLAN. Then, configure a priority value and a track object with a priority cost.

OS10-A(config)# interface vlan 20
OS10-A(conf-if-vl-20)# vrrp-group 1
OS10-A(conf-vlan20-vrid-1)#priority 120
OS10-A(conf-vlan20-vrid-1)# track 1 priority-cost 20

Configure track objects under a VRRP group. You can configure a maximum of four track objects under a VRRP group.

OS10-A(conf-vlan20-vrid-1)# track 2 priority-cost 30
OS10-A(conf-vlan20-vrid-1)# track 3 priority-cost 25
OS10-A(conf-vlan20-vrid-1)# track 4 priority-cost 40
OS10-A(conf-vlan20-vrid-1)# track 5 priority-cost 25

Configure a priority cost value that is less than the configured VRRP group priority value.
```
OS10-A(conf-vlan20-vrid-1)# track 2 priority-cost 254
```
If you change the VRRP group priority value to a value that is less than or equal to the priority cost value at a later point of time, the following error message displays: % Error: VRRP group priority cost cannot be greater than oper priority.
```
OS10-A(conf-vlan20-vrid-1)# priority 200
OS10-A(conf-vlan20-vrid-1)# track 2 priority-cost 190
OS10-A(conf-vlan20-vrid-1)# priority 110
```

Unconfigure the track1 object from the VRRP group and its BFD session.

OS10-A(conf-vlan20-vrid-1)#no track 1
OS10-A(conf-vlan20-vrid-1)# no bfd interface vlan 20 vrf default source-ip-address 11.11.11.1 neighbor-ip-address 11.11.11.2
OS10-A(conf-vlan20-vrid-1)#no track 1

NOTE: OS10 VRRP implementation supports a maximum of four tracking objects inside a VRRP group. These tracking objects can be either an interface or a BFD tracking object, or both. If you try to configure more than four tracking objects, the following error message displays: % Error: max-elements exceeded.

OS10 - VRRP secondary configuration

Create a track object and configure a BFD session.

OS10-B(config)# track 1
OS10-B(conf-track-1)#bfd interface vlan 20 vrf default source-ip-address 12.12.12.1 neighbor-ip-address 12.12.12.2 
interval 50 min_rx 50 multiplier 5 role active

Create a VLAN and a VRRP group under the VLAN. Then, configure a priority value and a track object with a priority cost.

OS10-A(config)# interface vlan 20
OS10-A(conf-if-vl-20)# vrrp-group 1
OS10-A(conf-vlan20-vrid-1)#priority 110
OS10-A(conf-vlan20-vrid-1)# track 1 priority-cost 20

Triggering immediate failover with priority zero packets

When a VRRP priority decrement occurs and it results in a VRRP priority is less than 1, VRRP advertisements with zero priority packets are sent. This activity triggers immediate failover. Immediate failover is faster when compared to the earlier method, where the VRRP backup node has to wait for the time duration of master_down_interval.

Omitting Skew time from master_down_interval calculation formula as defined in RFC5798

You are provided with an option to omit the skew time from the master_down_interval calculation. This option configures a lesser value for the master_down_interval and results in faster failover.

Global configuration

DELL(conf)#vrrp omit-skew-time

VRRP group level configuration

OS10(config)#vrrp-group 1
OS10(vrrp-group-1)#omit-skew-time
OS10(vrrp-group-1)#omit-skew-time disable

Following are the unconfigure commands:

OS10(vrrp-group-1)#no omit-skew-time
OS10(vrrp-group-1)#no omit-skew-time disable

By default, omit-skew-time is disabled both at the Global and VRRP group level.

When you configure group level omit-skew-time this configuration takes precedence over the Global level configuration.

Table 1. VRRP secondary configurationVRRP secondary configuration
Global level configuration	VRRP group level configuration	Expected behavior for this VRRP group
Default configuration or omit skew time disabled	Default configuration	Omit skew time is disabled.
Default configuration or omit skew time disabled	omit-skew-time	Omit skew time is enabled.
Default configuration or omit skew time disabled	omit-skew-time disable	Omit skew time is disabled.
VRRP omit-skew-time	Default configuration	Omit skew time is enabled.
VRRP omit-skew-time	omit-skew-time	Omit skew time is enabled.
VRRP omit-skew-time	omit-skew-time disable	Omit skew time is enabled.

When you enable omit-skew-time globally, it is applicable for all the VRRP groups. You can disable omit-skew-time for a subset of VRRP groups alone, by disabling it at the VRRP group level.

You can enable omit-skew-time only for a few VRRP groups, so that you can enable it at the VRRP group level. These VRRP groups are disabled at the Global level configuration.