The stack is formed by each node supplying a pair of full-duplex, logical stacking ports.
Summit X460-G2 with VIM-2q option card
Summit X480 switches with VIM3-40G4X option card
Summit X670V switches with VIM4-40G4X option card
Summit X670-G2-48x-4q with ports 57 and 61
128 Gbps: Summit X480 switches with VIM2-SummitStack128 option card
Summit X460 switches with SummitStack V80 option card
Summit X480 switches with VIM2-SummitStack-V80 option card, and VIM3-40G4X option card
Summit X670V switches with VIM4-40G4X option card
Summit X670G2-48x-4q with ports 57 and 61
Summit X440 switches
Summit X460 switches with SummitStack option card
Summit X480 switches with VIM2-SummitStack
Summit X460G2 switches with VIM-2SS option card
Even though two links are available, the links might not be fully utilized. For example, suppose there is a ring of eight nodes and the nodes are numbered clockwise from 1 to 8. The stacking port limit in this example is 10 Gbps in each direction for a total stack throughput of 20 Gbps for each port, or 40 Gbps total. Suppose node 1 wants to send 10 Gbps of unicast traffic to each of node 2 and node 3. The shortest path topology forces all traffic from node 1 over the link to node 2. Traffic from node 1 to node 3 passes through node 2. Thus, there is only 10 Gbps link available. However, if node 1 wanted to send 10 Gbps to node 2 and node 8, there would be 20 Gbps available because both links connected to node 1 would be used.
In a ring of eight nodes, between any two nodes (with one exception), only one link is used. If the devices provide 48 1-Gbps Ethernet ports, the overcommitment ratio between two such nodes is approximately 5:1. The exception is if there is an equal distance between the nodes. In this case, if both nodes are 48-port nodes, the nodes are grouped into two groups of 24 ports (by the hardware architecture), and thus it is possible to use both directions around the stack.
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