Can anyone say me what is MLAG ?

[Visconti]

Do anyone say me what is MLAG or LAG ?

[Eric_Burke]

In simple terms, mlag allows two core switches to look and act like a single redundant core. It helps to provide redundancy by allowing for one core to be taken offline (planned or unplanned) while maintaining connectivity to downstrean lag'd devices. It helps overcome the loss of connections to a core that would occur if it were stacked instead (firmware updates cause an entire stack to reboot - if your redundancy was via 2 stack members, you'd lose it during an update).

[Eric_Burke]

I should note, it can be used anywhere (not just the core), but it's more commonly seen there...

[Largetrousers]

LAG = link aggregate group, typically using LACP, a bond of 2 or more links to form an aggregated link. In EXOS terms this would be done using the sharing command

MLAG = Multi (Chassis) Link Aggregation Group. A configuration that is typically applied to 2x devices that from a layer 2 perspective act as one logical path for a LAG'd device to connect to. Probably better explained with images:

http://4.bp.blogspot.com/-NTp1ZGn-m3U/ULu7HIwXv0I/AAAAAAAAAJM/TUYSqyOYsdU/s1600/mlag_2.jpg