netdev - Re: cascaded switch

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Date:   Fri, 18 May 2018 23:40:35 +0300
From:   Ran Shalit <ranshalit@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org
Subject: Re: cascaded switch

On Fri, May 18, 2018 at 11:29 PM, Andrew Lunn <andrew@...n.ch> wrote:
>> Hi,
>>
>> I mean the same terminology used in marvell's switch.(I don't think
>> there is more than one terminology for this, please correct me if
>> wrong).
>> Anyway, I can see examples how it is done, but I don't understand the
>> benefit of this constellation, and why device tree needs to be
>> familiar with it.
>>
>> <   switch 1  >---port10--------port10- <  switch 2 >
>>  | ....|         |                                             | ....|    |
>> port 1-9     |                                      port 1-9     |
>>                  |                                                        |
>>                  |                                                        |
>> <cpu>--mdio----------------------------------------------
>
> Your ASCII art is all messed up, but i get what you mean.
>
> This is the D in DSA. You would use this when a single switch does not
> have enough ports for your use case. So you use two switches.
>
> You need to tell each switch what links are used to get to other
> switches. There is an internal routing table. So you need to describe
> these links in device tree.
>

I understand, thanks,
So, it is used so that the 2 switch will behave as if it is one big switch.

Yet, how does it change the way the ports appears in "ifconfig" ?
Is it that if they were separate switch I wouldn't see incremental
numbers in "lanX" in ifconfig  (as is probably the result in cascaded
switch) ?

Regards,
ranran

>       Andrew