Interview Questions.

Question 1. What Is Trex?

Answer :

TRex is speedy sensible open supply site visitors technology device, strolling on wellknown Intel processors, based on DPDK. It helps both stateful and stateless site visitors generation modes.

Question 2. What Are The Common Use Cases For Trex?

Answer :

High scale benchmarks for stateful networking equipment. For instance: Firewall/NAT/DPI.
Generating high scale DDOS attacks.
High scale, flexible checking out for switches (e.G. RFC2544)
Scale checks for huge numbers of customers/servers for controller based testing.
EVENT and manufacturing tests.
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Question three. Who Uses Trex?

Answer :

Cisco systems, Intel, Imperva, Mellanox, Vasona networks and much greater.

Question 4. What Are The Stateful And Stateless Modes Of Operation?

Answer :

“Stateful” mode is meant for trying out networking equipment which saves nation consistent with flow (5 tuple). Usually that is finished by injecting pre-recorded capture files on pairs of interfaces of the tool underneath take a look at, and dynamically changing src/dst IP/port.

“Stateless” mode is meant to test networking tools that doesn't manage any country consistent with go with the flow (as an alternative operating on a in keeping with packet basis). This is commonly performed via injecting custom designed packet streams to the tool below take a look at.

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Question five. Can Trex Run On A Hyper Visor With Virtual Nics?

Answer :

Yes. Currently there's a need for two-three cores and 4GB reminiscence. For VM use case, memory requirement can be extensively reduced if wanted (at the fee of assisting less concurrent flows) by the use of the subsequent configuration.

Limitations:

Using vSwitch will restrict the maximum PPS to round 1MPPS (DPDK-OVS/VPP can remedy this).
Latency effects will not be accurate.
For high overall performance setup (multi-rx-queue), it is better to feature rx_desc: 4096 within the trexd_cfg.Yaml see platform_yaml_cfg_argument and software mode.
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Question 6. Which Nics Are Supported / Why Not All Dpdk Supported Nics Supported By Trex?

Answer :

We are the use of precise NIC capabilities. Not all of the NICs have the skills we need.

We have regression assessments in our lab for every encouraged NIC. We do now not claim to help NICs we do now not have in our lab. You can locate the listing of supported NICs here. Look for “Supported NIcs” desk.

Notice that a few unsupported NICs also can be used the use of --software program command line argument.

Question 7. Is Cisco Vic Supported?

Answer :

Yes. Since model 2.12, with these limitations. Especially notice that a brand new firmware version is needed.

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Question eight. Is 100gbs Nic Sfp+ Supported?

Answer :

Mellanox Connectx 4 is supported. Connect three and five nevertheless have troubles (WIP to restoration). Support for FM10K is below development.

Question 9. What Is The Maximum Number Of Ports Per Trex Application?

Answer :

16 ports.

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Question 10. I Cannot See All sixteen Ports Statistics On Trex Server?

Answer :

We present information best for first 4 ports because there's no console space. Global information (like total TX) is correct, taking into consideration all ports. You can use the GUI/console or Python API, to see records for all ports.

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Question 11. Can I Use Multiple Types Of Ports With The Same Trex Server Instance?

Answer :

No. All ports in the configuration document should be of the same NIC type.

The workaround is to run several TRex times.

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Question 12. What Is Better, Running Trex On Vm With Pci Pass Through Or Trex On Bare Metal?

Answer :

Bare metallic can have lower latency and higher overall performance. VM has the advantages you generally get whilst the usage of VMs.

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Question 13. I Have Intel X710 Nic With four X 10 Gb/sec Ports And I Cannot Get Line Rate.

Answer :

X710da4fh with four 10G ports can reach a maximum of 40MPPS (general for all ports) with sixty four bytes packets. (Can not attain the theoretical 60MPPS restrict). This is still higher than the Intel x520 (82559 based totally) that may reach ~30MPPS for two ports with one NIC.

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Question 14. I Have Xl710 Nic With 2 X forty Gb/sec Ports And I Can Not Get Line Rate?

Answer :

XL710-da2 with 2 40G ports can reach most of forty MPPS/50Gb (general for all ports) and now not 60 MPPS with small packets (64B) Intel had in thoughts redundancy use case after they produced a  port NIC. Card become not intended to reach 80G line charge.

Question 15. I Want To Contribute To The Project?

Answer :

You have several ways you may help:

Download the product, use it, and file problems (If no problems, we can be very glad to also pay attention success testimonies).
If you operate the product and have improvement recommendations (for the product or documentation) we will be glad to listen.
If you restore a trojan horse, or increase new function, you're extra than welcome to create pull request in GitHub.
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Question sixteen. What Is The Release Process? How Do I Know When A New Release Is Available?

Answer :

It is a continuous integration. The ultra-modern inner model is underneath 24/7 regression on few steps in our lab. Once we've enough content we release it to GitHub (Usually every few weeks). We do not send an e-mail for each new launch, as it may be too common for some human beings. We announce huge characteristic releases on the mailing list. You can constantly check the GitHub of course.

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Question 17. During Os Installation, Screen Is Skewed / Error "out Of Range" / Resolution Not Supported Etc?

Answer :

Fedora - in the course of set up, choose "Troubleshooting" → Install in simple graphic mode.
Ubuntu - try Ubuntu server, which has textual installation.
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Question 18. Trex Traffic Does Not Show Up On Wire Shark, So I Can Not Capture The Traffic From The T Rex Port?

Answer :

TRex makes use of DPDK which takes possession of the ports, so the usage of Wire shark isn't viable. You can use transfer with port mirroring to seize the site visitors.

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Question 19. Trex Is Connected To A Switch And I Observe Many Dropped Packets At Trex Startup?

Answer :

A switch might be configured with spanning tree enabled. TRex reset the port at startup, making the transfer reset it aspect as well, and spanning tree can drop the packets until it stabilizes. Disabling spanning tree can help. On Cisco nexus, you can do this the usage of spanning-tree port type edge You also can start TRex with -okay <num> flag. This will ship packets for okay seconds earlier than starting the real test, letting the spanning tree time to stabilize. This trouble can be fixed when we consolidate “Stateful” and “Stateless” RPC.

Question 20. Why The Performance Is Low?

Answer :

TRex overall performance relies upon on many elements:

Make sure trexd_cfg.Yaml is best see "platform" section in manual.
More concurrent flows will lessen the overall performance.
Short flows with one/two packets (e.G. Cap2/dns.Yaml) will supply the worst performance.
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Question 21. Is There A Plan To Add Tcp Stack?

Answer :

Yes. We recognise that is some thing many human beings would really like, and are operating on this. No ETA but. Once a development is made, we will announce it at the T Rex sight and mailing listing.

Question 22. I Want To Have More Active Flows On The Dut, How Can I Do This?

Answer :

After stretching TRex to its most CPS potential, don't forget the following: DUT can have lots greater active flows in case of a UDP flow due to the character of growing older (DUT does not know whilst the flow ends even as TRex knows). In order to artificially growth the length of the energetic flows in TRex, you could config large IPG within the YAML record. This will cause each glide to closing longer. Alternatively, you can boom PH on your PCAP document as properly.

Question 23. Some Of The Incoming Frames Are Of Type Sctp. Why?

Answer :

Default latency packets are SCTP, you may miss the -l <num> from command line, or exchange it to ICMP.

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Question 24. Is Multi-person Supported?

Answer :

Yes. Multiple TRex clients can connect to the identical TRex server.

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Question 25. Can I Create Corrupted Packets?

Answer :

Yes. You can construct any packet you like the usage of Scapy. However, there is no way to create corrupted L1 fields (Like Ethernet FCS), on the grounds that these are typically treated by the NIC hardware.

Question 26. Can I Have A Synchronization Between Different Stream Variable?

Answer :

No. Each circulation has its own, separate subject engine application.

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Question 27. Is There A Plan To Have Luajit As A Field Engine Program?

Answer :

It is a wonderful idea to feature it; we're seeking out someone to contribute this guide.

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Question 28. Are You Recommending Trex Hltapi?

Answer :

TRex has minimal and fundamental guide for HLTAPI. For simple use instances (with out latency and in step with flow statistic) it'll probably paintings. For advanced use cases, there's no substitute for native API that has complete control and in maximum instances is less complicated to apply.

Question 29. Can I Test Qos Using Trex?

Answer :

Yes. Using Field Engine you could build streams with specific TOS and get statistic/latency/jitter consistent with stream.

Question 30. What Are The Supported Routing Protocols Trex Can Emulate?

Answer :

For now, none. You can join your router to a transfer with TRex and a device going for walks routes. Then, inject routes using course, and different visitors the use of TRex.