Use the VIM1-SummitStack512 Module

The VIM1-SummitStack512 versatile interface module allows you to connect two Summit X650 series switches in a cross-over or back-to-back configuration, using SummitStack 128G cables.

This configuration provides two bidirectional links operating at 256 Gbps between the two switches.
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Stacking Connections Using VIM1-SummitStack512 Modules and SummitStack 128G Cables
Unlike other stacking configurations, with the VIM1-SummitStack512 modules, ports are connected in pairs of matching port numbers. When you connect stacking cables to installed VIM1-SummitStack512 modules, match the stacking ports as listed in Using the V1M1-SummitStack512 Module: Connections.
Table 1. Using the V1M1-SummitStack512 Module: Connections
Connect this slot and port . . . . . . To this slot and port
Slot 1 Stack Port 1 Slot 2 Stack Port 1
Slot 1 Stack Port 2 Slot 2 Stack Port 2
Slot 1 Stack Port 3 Slot 2 Stack Port 3
Slot 1 Stack Port 4 Slot 2 Stack Port 4