Dell BigIron RX Series, Configuration Manual

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436 BigIron RX Series Configuration Guide
53-1002253-01
Configuring optional VSRP parameters
15
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Backup Hello interval
•
Hold-down interval
Each Backup saves the configured timer values to its startup configuration file when you save the
device’s configuration.
NOTE
The Backups always use the value of the timer scale received from the Master, regardless of whether
the timer values that are saved in the configuration are the values configured on the Backup or the
values received from the Master.
VSRP slow start
In a VSRP configuration, if a Master router goes down, the Backup router with the highest priority
takes over. When the Master comes back up again, it takes over from the Backup. By default, this
transition from Backup back to Master takes place immediately. You can configure the VSRP slow
start timer feature, which causes a specified amount of time to elapse between the time the
Master is restored and when it takes over from the Backup (This range is currently set to between 1
to 600 ticks (1/10 second to 60 seconds). This interval allows time for VSRP convergence when
the Master is restored.
To set the VSRP slow start timer to 3 seconds, enter the following command.
BigIron RX(config)# router vsrp
BigIron RX(config-vsrp-router)# slow-start 30
Syntax: slow-start <ticks>
The ticks parameter can range from 1 to 600 ticks (1/10 second to 60 seconds).
When the VSRP slow start timer is enabled, if the Master goes down, the Backup takes over
immediately. If the Master subsequently comes back up again, the amount of time specified by the
VSRP slow start timer elapses (in this example, 3 seconds) before the Master takes over from the
Backup.
Changing the Time-To-Live (TTL)
A VSRP Hello packet’s TTL specifies how many hops the packet can traverse before being dropped.
A hop can be a Layer 3 Switch or a Layer 2 Switch. You can specify from 1 – 255. The default TTL is
2. When a VSRP device (Master or Backup) sends a VSRP Hello packet, the device subtracts one
from the TTL. Thus, if the TTL is 2, the device that originates the Hello packet sends it out with a TTL
of 1. Each subsequent device that receives the packet also subtracts one from the packet’s TTL.
When the packet has a TTL of 1, the receiving device subtracts 1 and then drops the packet
because the TTL is zero.
NOTE
An MRP ring is considered to be a single hop, regardless of the number of nodes in the ring.
To change the TTL for a VRID, enter a command such as the following at the configuration level for
the VRID.
BigIron RX(config-vlan-200-vrid-1)# initial-ttl 5
Syntax: [no] initial-ttl <num>
The <num> parameter specifies the TTL and can be from 1 – 255. The default TTL is 2.