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I have already given a non-technical synopsis on VLT in one of my previous posts here https://hasanmansur.com/2012/10/15/force10-s4810-stacking-vs-vlt/
As mentioned, VLT Is a 
Dual Active Control Plane implementation, of a Multi System LAG. Cisco vPC is a similar technology.
VLT is beneficial in environments where the downstream devices like servers or access/distribution switches need to build port channels/LAGs across two separate upstream switches. in this context, VLT resembles what stacking offers. The other benefit is that due to distinct control planes, it is possible to perform maintenance one switch at a time without taking the entire fabric down. This is unlike stacking, where the entire fabric must be taken down for upgrades etc.
Here, i will provide a quick configuration sample on getting VLT operational between two VLT peer (S4810) switches.
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| VLT | ||||
| VLT – Backup Link | FTOS(conf)# | interface TenGigabitEthernet | 0/xx | You must configure the backup link before you can configure the VLT trunk interconnect. Here, i am connecting an in-band L3 link back-to-back between the peers. |
| description To VLT peer – backup link | ||||
| ip address | x.x.x.x/24 | |||
| no shutdown | ||||
| exi | ||||
| Port-Channel (VLTi) | ||||
| FTOS(conf)# | interface Port-channel | 100 | Enter the same port-channel number configured with the peer-link port-channel command in the Enable VLT and create a VLT Domain steps |
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| description VLTi To | peer-switch | |||
| channel-member fortyGigE | 0/48 | |||
| channel-member fortyGigE | 0/56 | |||
| vlt-peer-lag port-channel | 100 | |||
| no shutdown | ||||
| exi | ||||
| VLTi member ports | FTOS(conf)# | interface fortyGigE | 0/48 | |
| FTOS(conf-if-fe-0/48)# | description To VLT peer – VLTi | |||
| FTOS(conf-if-fe-0/48)# | no ip address | |||
| FTOS(conf-if-fe-0/48)# | no shutdown | |||
| FTOS(conf-if-fe-0/56)# | exi | |||
| FTOS(conf)# | interface fortyGigE | 0/56 | ||
| FTOS(conf-if-fe-0/56)# | description To VLT peer – VLTi | |||
| FTOS(conf-if-fe-0/56)# | no ip address | |||
| FTOS(conf-if-fe-0/56)# | no shutdown | |||
| FTOS(conf-if-fe-0/56)# | exi | |||
| VLT Domain | FTOS(conf)# | vlt domain | 1 | |
| peer-link port-channel | 100 | IP address of the interface on the remote VLT peer to be used as the endpoint of the VLT backup link for sending out-of-band hello messages. | ||
| back-up destination | x.x.x.x | |||
| primary-priority | 1 | |||
| unit-id | 0 | |||
| exi | ||||
| VLT Downstream clients | FTOS(conf)# | interface port-channel | 1 | Port-Channels to Servers |
| no ip address | ||||
| Servers | switchport | |||
| spanning-tree rstp | edge-port | |||
| channel-member tenGigE | 0/1 | |||
| no shutdown | Associate the port channel to the corresponding port channel in the VLT peer for the VLT connection to an attached device. | |||
| vlt-peer-lag port-channel | 1 | |||
| exi | ||||
| FTOS(conf)# | interface TenGigabitEthernet | 0/1 | ||
| description To downstream | Server xyz | |||
| no ip address | ||||
| port-channel-protocol | LACP | |||
| port-channel | 2 mode active | Channel # 2 is the downstream PoCH to the server, on each peer. | ||
| no shutdown | ||||
| exi | ||||
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This ofcourse, will need to be repeated on the VLT peer Switch as well, and the values that need changing will have to changed.
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Hasan Mansur 
Reblogged this on staniislaus.