[j-nsp] QSA adapters and MTU

[Eduardo Lopes de Haro]

Hi,
Here is the public documentation of MX304 mentioning the MTU limitation for 1G:
https://www.juniper.net/documentation/us/en/software/junos/interfaces-ethernet/topics/ref/statement/speed-gigether-options.html


  *   On MX304 for 1G interface, the maximum MTU supported is 2000 bytes. Hence, the maximum MRU supported is 2008 bytes.

Br.,
--
Eduardo Haro



Juniper Business Use Only

From: juniper-nsp <juniper-nsp-bounces at puck.nether.net> on behalf of Ola Thoresen via juniper-nsp <juniper-nsp at puck.nether.net>
Date: Friday, 3 November 2023 12:16
To: juniper-nsp at puck.nether.net <juniper-nsp at puck.nether.net>
Subject: Re: [j-nsp] QSA adapters and MTU
[External Email. Be cautious of content]


On 03.11.2023 16:04, Chris Wopat wrote:

> 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.
>
This is the same use case as for us, and my understanding is exactly
that they are just passing a single lane through, and should not really
know anything about packets or ethernet frames or anything.

But still - people more knowledgeable than me - assure me that there is
a limit of 2008 Bytes MTU - at least for 1G.

I just can't find this documented anywhere, and I would have thought
that more people would have made more fuss about it when they start
using it if this is a real issue.


> 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.
>
Yes. They list QSA adapter as supported, also for 1G optics, and don't
write anything about any MTU limitations in the Hardware Compatibility Tool.


/Ola (T)

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