Network Tuning UDP (e.g BDP)

[TrevorB]

I've taken the RH442 once in RHLS and once live with a trainer. The student workbook does not have a UDP tuning section, there is no guided excercise or labs for UDP tuning. However it is an exam question on EX442. 

• I've search the RH442v80 student workbook PDF table of contents and performed find for every reference to UDP.
• I've searched the RH KB's, one talks about TCP, it then links to another on Bandwidth Delay Product, and that URL is access denied.
• I've hunted the internet for a discussion which covers UDP tuning in Linux, instead of generic discussion or specific Cisco router threads.
• I backtracked and found my old RH442v7 student workbook and looked through it as well, but not all words appear to be searchable in the PDF, so possible I overlooked something.

Nothing so far has pointed me in the correct direction to find an answer which is explicit in the exact kernel tunables to modify.

My suspicion is that it's max is the net.core _max, and that UDP min would simply be the net.core _default tunables:

• net.core.rmem_max
• net.core.wmem_max
• net.core.rmem_default
• net.core.wmem_default

However there is also which I cannot find discussed during the course content either:

• net.ipv4.udp_rmem_min
• net.ipv4.udp_wmem_min (listed as non effective since UDP has no tx memory accounting)

I'm honestly frustrated. I've always held Red Hat training courses in the highest regards when it comes to actually preparing the student for the examination. I've almost always been able to go back to the training content to find an answer I overlooked or was not discussed in detail during the course. However in this case I feel I have exhausted many directions of investiation and do not feel it was included in ANY of the course content unless it once was and was removed from the course, but not removed from the exam. Am I just missing something or hitting non searchable PDF content?

Thanks in advance to anyone who has suggestions, even if its "you clearly overlooked page XYZ of student guide" etc.

[TrevorB]

I found a Knowledge Base article which I guess should be the "source of truth". It includes a UDP Buffers section. I thought tuning was requested for both read/write, and this article states its only available for read. I could easily be misremembering and only the TCP tuning requirements required both directions.

I cannot find this in my student workbook, or in RHEL 8 Configuring and Managing Networking or Monitoring and Managing System Status and Performance. I do find the same reference in an older RHEL7 Network Performance Tuning PDF. Except it only mentions net.core.rmem_max, nothing about net.core.rmem_default which the KB article does mention, so its potentially conflicting information about what to do.

Too bad its not included in the RH442 student workbook. If the TCP and UDP kernel params were identical I could see leaving this out entirely and just say apply the same logic. That isn't viable and the net.core values to change also impact TCP.

This is one of the very few, and I'd say the worst, omission of one of the Red Hat courses I have taken which they expect a solution during the exam. I would wager a high percentage of students miss by very very few points and require a retake of this exam. I know 5 RHCA's, 2 who worked at Red Hat when they achieved the cert. All 5 state this is the hardest Red Hat exam they ever took, personally I think its because the training content has diverged from the exam tasks more than any other exam I have taken from Red Hat.

This could easily still be the hardest exam, but the content could still better prepare the students to attempt it.

[Trevor]

Hello TrevorB,

You didn't indicate in your post that you had attempted the EX442 exam.  However, I am curious if you did sit for th exam, because of this part in your post - "...there is no guided excercise or labs for UDP tuning. However it is an exam question on EX442."

I've looked at the exam objectives for the EX442 for quite some time now, and just did a drive-by before my post, to see if there had been an update to the objectives.  I didn't see anything new in the objectives.  

I know I"m not providing any info to assist in your query, but if you don't mind assisting me, may I learn where you found that "UDP tuning" is an exam objective for EX442.  You may have gotten some information from your live training that is note worthy to the community at large.

Thanks TrevorB.

[TrevorB]

Hello Trevor,

Yes, I have sat for the EX442, and more than once unfortunately. I highly suggest you and anyone else familiarize yourself with the free retake policy discussion here. My second attempt is the only time I've noticed a retake offered, so I suspect some people (including myself!) may be purchasing their retakes when they could attempt it once for free.

FWIW I have had this UDP tuning question every single time regardless of which "domain" I was testing in. I also believe there was no variation in the task from what I recall. I wish I could elaborate more but with the NDA I am nervous about posting as much as I have already :smile: 

Good luck on your exam,
TrevorB

[Trevor]

Hello TrevorB,

Wow!  Your post is paying multiple dividends.  

By your having taken the EX442 exam, your comment about UDP Tuning being a question on the exam is authoritative!!!  Thank you so very much for that.

Another very beneficial dividend from your post is the announcement of the retake policy.  Your disclosure about this is breaking news.  If that item is published somewhere, it certainly is in fine print. Thanks to you, it's now out in the open!!!

It makes sense, to me anyway, that something related to network tuning would be on the exam each time.  As per the exam objectives, "Tune Network Performance" is one of the seven major sections in the list of objectives.  The nugget that you provided is that specifically, the tunining involves UDP tuning.  I don't think that disclosure is encroaching on violating the NDA.  

Well, after receiving training from two different sources, and then failing to cross the finish line on more than one exam attempt, I can appreciate your frustration as it relates to the challenge in getting clarification on this one item. 

Okay, now that I've used up some of your bandwidth in getting information, let me saddle up to see what information I can find, to be able to contribute to the cause.

Many thanks TrevorB

[TrevorB]

Without encroaching on the NDA I'd also highly suggest investigating PCP Folio's. The guide does cover CLI tools which can be used, but combining with grep and awk and large amounts of data flying up the screen may be a bit hard to correlate or time consuming when already under pressure.

If nothing else the UI could help quickly to visually confirm CLI findings before submitting the answer.

[Trevor]

Gotta give you one more thanks TrevorB on the suggestion to investigate
PCP Folio's.

Many, many, thanks!!!

[AbdulRehman]

Hi @TrevorB 

Thank you for the valuable information you have provided, I'm also planning to attempt EX442 soon.

Apart from the above you mentioned, do you think RHLS 442 course would be enough to pass the exam or we need other trainings too?

Thanks again.

Abdul Rehman