Dell PowerSwitch S4128F-ON OS10 Enterprise Edition User Guide Release 10.4.3.0 - Page 1046

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 differentiate 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. Configure the VLT backup link using the backup destination {ip-address | ipv6 ipv6-address} [vrf management] [interval interval-time] Example configuration: 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 different 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 flooding of traffic instead of unicast. Due to wrong hashing, ARP learning might fail leading to traffic 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 traffic from Host1 is hashed to VLT peer2, then the VLT peer2 floods the traffic. Yet, the traffic would not reach Host2 as the VLT port between VLT peer 2 and Swicth 3 is down. 1046 Virtual Link Trunking