[j-nsp] MX routers and DAC cables?

[aaron at digitalcrossroad.org]

Seconding Eric's point, depending on the version of Junos and transceiver, fec will be auto-configured, can be turned off, but depending on the transceiver, for example CWDM4, fec must be enabled on both sides to get link-up.

Along with disabling auto-negotiation on one side or both can sometimes help.

Just make sure to wait 1min after committing as  changes to take effect can be delayed.

-Aaron

Jun 12, 2020, 13:55 by eric at telic.us:

> That's what I was going to chime in on.  Behaviour differences between
> software versions have done different defaults. 
>
> ekrichbaum at atl-bdr1> show interfaces et-0/0/1 | grep FEC 
>  Active defects : None
>  Ethernet FEC Mode  :                   NONE
>
> eric at cht-bdr2> show interfaces et-0/0/1 | grep FEC 
>  Active defects : None
>  Ethernet FEC Mode  :                  FEC91
>
> These are 204s with a difference in default from 17.4 to 18.2 somewhere.
> Manually setting FEC on both ends seems to correct and bring up the links.
>
>
> -----Original Message-----
> From: juniper-nsp <juniper-nsp-bounces at puck.nether.net> On Behalf Of Tobias
> Heister
> Sent: Friday, June 12, 2020 2:03 PM
> To: juniper-nsp at puck.nether.net
> Subject: Re: [j-nsp] MX routers and DAC cables?
>
> Hi,
>
> On 12.06.2020 20:39, Chris Adams wrote:
>
>> Is anybody using DAC cables on MX routers?  We have a customer with an
>> MX10003 connected to EX4600 switches with 40G DAC cables (Juniper 
>> parts, not third-party).  Upon upgrading the router JUNOS to 
>> 18.2R3-S3, none of the interfaces with a DAC cable would come up on the
>>
> router end.
>
>>
>> JTAC's response was that no DAC cables are supported on any MX routers.
>>
>> That seems a little odd to me... I thought DAC cables are a part of 
>> the various specs, so saying they're not supported is saying those 
>> aren't actually Ethernet ports to me.
>>
>
> DAC and AOC are transceivers, and officially only a specific set of
> transceivers are supported per platform.
>
> For MX10003 you can check here: 
> https://apps.juniper.net/hct/product/#prd=MX10003
>
> There are 40GE AOC supported for that box, but not 40GE DAC. For 100GE DAC
> are actually supported in later Junos version.
>
> That being said typically DAC worked in MX for 10G and even 40G on most
> noxes, but on MX10003 we had a lot of problems with 40G DACs and eventually
> replaced most/all of of them with optical transceivers.
>
> Even on 100GE you might need to set the FEC config depending on what and
> where you connect the other DAC end.
>
> While 10G mostly worked everywhere we had a fair share of trouble on 40 and
> 100GE on various vendors and platforms.
>
> --
> regards
> Tobias
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