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Exam 70-740 topic 1 question 165 discussion

Actual exam question from Microsoft's 70-740

Question #: 165
Topic #: 1

HOTSPOT -
You deploy a new Hyper-V host named Server1 that runs Windows Server 2016.
You implement receive side scaling (RSS) on Server1.
The chipset on Server1 does not support NetDMA.
All of the equipment on your network supports 10-Gbps connectivity.
On Server1, you deploy a virtual machine named VM1.
You configure VM1 to aggregate all of the Windows and non-Windows log files for all of the servers on the network.
VM1 has four virtual processors.
You discover that VM1 drops packets.
Which two options should you run? To answer, select the appropriate options in the answer area.
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by coleman at Oct. 7, 2019, 9:04 a.m.

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hkshado

Highly Voted 5 years, 8 months ago

I think the first action is enabling VMQ as vRSS dependent on this.

upvoted 5 times

lbs

5 years ago

The dependency of vRSS on VMQ ties the 2 answers together.

upvoted 4 times

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Dave_Holden

Most Recent 4 years, 6 months ago

Well, according to this page (see below) TCP Chimney Offload doesn't work with Hyper-V, so I don't see how enabling it would help resolve the problem here. See the table under heading "How TCP Chimney Offload coexists with other programs and services" https://support.microsoft.com/en-ca/help/951037/information-about-the-tcp-chimney-offload-receive-side-scaling-and-net

upvoted 1 times

Dave_Holden

4 years, 6 months ago

This page further discourages the use of TCP Chimney Offload, stating that in 2016 it is deprecated. Under Heading Hyper-V Networking Configuration Best Practices. Do not use TCP Chimney Offloading or IPsec Offloading with Windows Server 2016. These technologies have been deprecated in Windows Server 2016 and can impact server and networking performance. To disable TCP Chimney Offload, from an elevated command prompt run the following commands: Netsh int tcp show global – This shows the current TCP settings netsh int tcp set global chimney=disabled – Disables TCP Chimney Offload, if enabled https://www.vembu.com/blog/hyper-v-networking-best-practices/

upvoted 1 times

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Dave_Holden

4 years, 6 months ago

I say that the correct answer is: First Action: Enable virtual machine queue (VMQ) on Server1 and VM1 Second Action: Enable virtual Receive-side Scalling (vRSS) on VM1. I invalidate any SR-IOV options as the solution here because SR-IOV is a very hardware specific solution. We are not given any information, clues or confirmation that SR-IOV is supported with the hardware in this case. We can't just assume that it is. We are however given information that confirms that RSS is supported. >>> "You implement receive side scaling (RSS) on Server1." <<< So with that information and the knowledge that RSS and VMQ are both technologies intended to be used together, they look to be the right answers. By deduction I rule out TCP Chimney Offload by invalidating it as well, (see my other post). By deduction I am also invalidating SR-IOV, again based on the lack of confirmed hardware support.

upvoted 1 times

Dave_Holden

4 years, 6 months ago

I further disqualify SR-IOV because to enable it correctly the first action would have to be to enable it on server1 and then enable it on VM1. Here we are given as first action to enable SR-IOV on VM1 and Second action to enable SR-IOV on Server1. This is not possible. SR-IOV to be enabled first on the server would require that it's turned on in the BIOS and then a new external vSwitch would need to be created, where it would be enabled on the switch. Then SR-IOV would need to be enabled on the vNIC of VM1. So again by deduction SR-IOV is invalidated.

upvoted 1 times

Dave_Holden

4 years, 6 months ago

I do however agree that the optimal solution would be SR-IOV if possible with hardware support and the right steps were provided.

upvoted 1 times

Dave_Holden

4 years, 6 months ago

SR-IOV is rather finicky and only works best in the right situations and workloads. Some more context on this page, as well as further evidence disqualifying TCP Chimney Offload. See Headings: SR-IOV TCP Chimney Offload https://statemigration.com/network-offload-and-optimization-technologies-in-windows-server-2016/

upvoted 1 times

Dave_Holden

4 years, 6 months ago

There is a great feature compatibility table as well in the statemigration.com link. See Heading Feature mutual compatibility at the bottom of the page.

upvoted 1 times

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seriouslyms

4 years, 6 months ago

Well i typed out a full explanation for this question and got timedout. Awesome. The answer is SR-IOV for both. TLDR you have no switch, enabling SR-IOV can be done on both VM1 and Server1, and it's a requirement to do so. You also create the switch in the process of enabling it on Server1, as you can only enable it when you create a new switch. TCP offload is discouraged by MS. It also doesn't help packet loss. VMQ is a requirement for vRSS, it also doesn't help packet loss. It also is enabled by default. Therefore it's impossible to enable it again.

upvoted 1 times

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jam7272

4 years, 11 months ago

I would go for VMQ and RSS - they are both related to offloading to CPU and there are enough vCPUs in this example. VMQ and RSS compliment eachother.

upvoted 3 times

seriouslyms

4 years, 6 months ago

You are WRONG. VMQ AND vRSS ARE ENABLED BY DEFAULT, ALREADY.

upvoted 1 times

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panda

5 years ago

I think the given answers are correct. First action: Enable TCP Chimney Offload on Server1 Second action: Enable virtual Receive-side Scallng (vRSS) on VM1 Since no Net DMA, SR-IOV and DMA can't be used. Since RSS implemented, RSS and TCP Chimney Offload (*1) can be used. (*1)https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/gg162709(v=ws.10)?redirectedfrom=MSDN

upvoted 3 times

panda

4 years, 11 months ago

I made mistake. The first answer is VMQ. Because TCP Chimney isn’t related to packet loss, which takes processing from CPU to network adapter, popca11 said.

upvoted 1 times

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mazintaha

5 years ago

this is what i came up to for the first answer: SR-IOV cannot be enabled for -VM!- only for Server, right, so scratch that option vRSS cannot be enabled for -VM and Server!- only for VM, right, so scratch this option too and now we are left with TCP Chimney Offload on Server1, which is indeed can be enabled on server .. for the second answer: using the same concept, TCP Chimney .... cannot be enabled on VM!, only on Server, right vRSS cannot be enabled on VM!, only on server, right SR-IOV can be enabled on Server1, soit will be the answer

upvoted 2 times

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alexnt

5 years ago

Which is the correct answer for the first action?

upvoted 1 times

alexnt

5 years ago

Is DMA necessary for VMQ?

upvoted 1 times

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popcar11

5 years, 1 month ago

Read Carefully about TCP This feature is designed to take processing of the network such as packet segmentation and reassembly processing tasks, from a computer's CPU to a network adapter that supports TCP Chimney Offload. This has the effect of reducing the workload on the host CPU and moving it to the NIC, allowing both the Host OS to perform quicker and also speed up the processing of network traffic.

upvoted 3 times

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Jake__

5 years, 2 months ago

Got this Q on exam

upvoted 4 times

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rjc

5 years, 5 months ago

Here the link on vmq need dma: https://portal.nutanix.com/#page/kbs/details?targetId=kA0600000008eNTCAY

upvoted 1 times

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rjc

5 years, 5 months ago

The question states: The chipset on Server1 does not support NetDMA. The following articles states: VMQ works by allowing a Network Interface Controller (NIC) to transfer incoming frames directly to the receive buffer of the NIC by using Direct Memory Access (DMA).... Can anyone help me am on the track about VMQ not being an option.

upvoted 1 times

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glukken

5 years, 6 months ago

I agree with both VMQ and vRSS. See hardware requirements in https://docs.microsoft.com/en-us/windows-server/networking/technologies/vrss/vrss-top

upvoted 3 times

glukken

5 years, 5 months ago

I think the main factor is the virtual RSS for the VM. I cannot find anything about NetDMA being necessary for VMQ to work, as VMQ is able to use DMA, but not specifically required. But VMQ IS required for virtual RSS (and not for RSS which is used at the (physical) host level). So if the second option is vRSS, the only possible answer could be VMQ for the first option. Again, this all has to do with the RSS at the VM level (=vRSS) and not at the host level (=RSS).

upvoted 4 times

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coleman

5 years, 8 months ago

anyone can explain why first action is enable TCP......?

upvoted 1 times

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