Connectivity Guide

Delay restore timer
When a VLT node boots up, restoration of VLT port status is deferred for a certain amount of time to enable VLT peers to complete the
control data information exchange.
If the peer VLT device was up at the time the VLTi link failed, the system allows a delay in bringing up of VLT ports after reload or peer-link
restoration between the VLT peer switches..
When both the VLT peers are up and running, and if VLTi fails, the secondary peer brings down the VLT ports. When the VLTi port comes
up, secondary peer does not bring up VLT ports immediately. The VLT ports are brought up only after the VLT port restoration timer, to
allow both the VLT peers to sync up the control information with each other.
By default, the system allows 90 seconds. You can use the delay-restore timer command to modify the duration of the timer.
Example:
OS10(config)# vlt-domain 1
OS10(conf-vlt-1)# delay-restore 100
VLT backup
VLT backup link is an additional link used to check the availability of the peer nodes in the VLT domain.
When VLTi interface goes down, the backup link helps to dierentiate the VLTi link failure from peer node failure. If the VLTi link fails, all the
VLT nodes exchange node liveliness information through the backup link.
Based on the node liveliness information, the VLT LAG/port is in up state in the primary VLT peer and in down state in the secondary VLT
peer. When only the VLTi link fails, but the peer is alive, the secondary VLT peer shuts down the VLT ports. When the node in primary peer
fails, the secondary becomes the primary peer.
Congure the VLT backup link using the backup destination {ip-address | ipv6 ipv6–address} [vrf management]
[interval interval-time]
Example conguration:
OS10(config)# vlt-domain 1
OS10(conf-vlt-1)# backup destination 10.16.151.110 vrf management interval 30
OS10(config)# vlt-domain 1
OS10(conf-vlt-1)# backup destination ipv6 1::1 vrf management interval 30
The following examples describe dierent cases where VLT backup link can be used:
Support for new streams during VLTi failure
When VLTi fails, MAC address learnt after the failure is not synchronized with VLT peers. This leads to continuous ooding of trac instead
of unicast.
Due to wrong hashing, ARP learning might fail leading to trac being dropped.
In the following illustration, after VLTi is down VLT peer1 learns MAC address of Host2.
As VLTi link fails, the VLT peer2 is not synched up with the MAC address of Host2 . Due to this, if the trac from Host1 is hashed to VLT
peer2, then the VLT peer2 oods the trac. Yet, the trac would not reach Host2 as the VLT port between VLT peer 2 and Swicth 3 is
down.
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Virtual Link Trunking