Connection over 2 stacking cables

[nikolami]

Hello,
In case of using 2 stacking cables to connect 2 AOS switches (OS6850, OS6400 or OS6250) what will be the throughput between these switches? Will connection over 2 stacking cable means that both stacking ports are simultaneosly used or one cable is active and the other cable is standby?

For example if we connect 2 OS6850 over 2 stacking cables what would be the throughput between switches (picture).


According to datasheet, OS6850 has 2 built-in 10 Gb/s full-duplex stacking ports and stacking capacity 40 Gbps. In one case throughput between switches will be 10 Gbps Full Duplex (just one stacking port on switch is active) or in other case 20 Gbps Full Duplex (both stacking port on switch are active)?

Regards,
nikolami

[cedric1]

hello

After reading HW guide, for me only one link pass traffic so you have 10GFullDuplex

Use command

From HW guide :

To check whether a redundant stacking cable connection exists between the top-most and bottom-most
switches in the stack, use the show stack status command. For example:
-> show stack status
Redundant cable status : present
Tokens used : 12
Tokens available : 20

Cedric

[nikolami]

Thank you Cedric.

But I'm not sure that this is a definite answer.

I finally found one Alcatel presentation for older OmniSwitch 6600. One slide is related to aggregate stacking throughput.



"In a configuration of more than two stack elements, the stacking link between elements can only be used up to two Gigabits per second because there is a loop topology that needs to be supported. When there are only two elements in a stack, the stacking link now has four Gigabits per second capacity because the two stacking links can act as an aggregate. This may be an important consideration when deploying the network if there is a need to have the highest possible throughput on the uplink ports. If you need a full four Gigabits per second of throughput on the uplinks and you want all of the ports to be able to take advantage of the potential bandwidth of the uplink ports, this may be a solution. Instead of a stack of four units, you may want to consider two stacks of two elements each. "
But I'm not sure what is the situation in practice? If someone tested this feature (especially on newer stackable OmniSwitches)?

Regards,
nikolami

[silvio]

Hi,
it's 20G FD with both stacklinks. You can find the answer in Boilerplate - search in BPW for it.

Stacking Capacity & Throughput:
Raw Capacity: 24Gbps FD (12Gbps FD “Stack-A” and 12Gbps FD “Stack-B”)
Throughput: The Stacking (Stack “A” & Stack “B” run at 10G) supports 2 x 10-Gigabit Eth ports at wire-speed: 2 * 14,880,952.3 pps = 29,761,904.6pps (approx: 29.8Mpps)


regards Silvio

[cedric1]

Hi all

I got this complete clarification with 2, 3 etc stacks connected wich overlap Silvio answer

Only in case you stack two units, you will use both stacking links (with Hashing algoritme). So you can go up to 20Gig.
In case you have more than two units in a stack, you will use the Shortest Path Algoritm in the ring. In that case between two units Maximum is 10Gig. But in that case you can have other traffic using the other Path in the ring.

Cedric

[nikolami]

Thank you Silvio and Cedric.

So definite answer is that only in case of 2 units (switches) in stack, througput between units will be 20Gbps FD, i.e. both stacking ports on switch are simultaneosly used.
In other cases, 3 and more units in stack, one stackin port on switch is used to send data to other switch in stack (througput between units will be 10Gbps FD).

Nikolami

[cedric1]

hello

you statement is correct

Cedric

[jiggsy72]

Do you get 20Gbps FDX by default when you insert both stack cables or is there a command to activate this?

[jlettinck]

Jiggsy,

It is automatically by default, you can not configure it.

[ram]

Hi Cedric/Slivio,

If i connect only two unit of 6850 stacking like from pri stack A to sec Stack b and sec stack A to Stack B means can i get 20 gbps please let me know...?

Regards,
Ram.