[j-nsp] QSA adapters and MTU

[Chris Wopat]

We use them on MX304 at 10g, primarily to get DWDM SFP+ to work. MTU is
fine, it's 9k as a part of LACP on a recent deployment. The adapter simply
passes through lane :0 to the port when configured as QSFP+. If you insert
the adapter and no optic, the device is unaware of its existence - you only
see the SFP+ info.

We haven't tested in prod on 1g but i think we did in the lab. can probably
toss something in there if you're really curious. I think the juniper
supported optic page lists QSA adapter support or not. I thought it was
generally supported with Junos 20+ nowadays.

me at mx304> show chassis pic fpc-slot 0 pic-slot 1 | match 14
  14   10GBASE ZR        SM    FLEXOPTIX          P.1596.80         1550 nm
                  0.0           1550nm   SFF-8472 ver 10.2


me at mx304> show interfaces terse | match xe-0/0/14
xe-0/0/14:0             up    up
xe-0/0/14:0.0           up    up   aenet    --> ae5.0


me at mx304> show interfaces ae5 | match mtu | match roto
    Protocol inet, MTU: 9000
    Protocol inet6, MTU: 9000
    Protocol mpls, MTU: 9166, Maximum labels: 3
    Protocol multiservice, MTU: Unlimited

Cheers
Chris


On Fri, Nov 3, 2023 at 8:01 AM Ola Thoresen via juniper-nsp <
juniper-nsp at puck.nether.net> wrote:

> Hi all,
>
> I am currently investigating the use of 1G and 10G optics on the MX304.
>
> This requires a QSA adapter -
>
> https://mellanox.my.site.com/mellanoxcommunity/s/article/all-about-qsa-adapter
> - That is fine.
>
> But then I hear people telling me that there is a known limitation when
> using these adapters that you can not have a higher MTU than ~2000 Bytes
> at _least_ when using 1G SFPs, but possibly also with 10G.  However, I
> can not find _any_ information about that anywhere.  Not from Juniper,
> not from Mellanox (Nvidia), nor from any user guides or datasheets I
> have found for the adapter from various vendors, and not from any mail
> archives, forums or anywhere else my Google-foo is taking me.
>
> Those who raised the issue are quite insistent that it is real, but they
> don't have any links or documents backing them up.  Is it just FUD?
>
> * Has anyone ever used these adapters?
>
> * In a Juniper device (they are supported on different platforms)?
>
> * With 1G or 10G SFPs?
>
> * With (or without) adjusting the MTU?
>
>
> /Ola (T)
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