esnet/iperf

DSCP bit appearing in different frame in iperf2 and iperf3-current

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#510 opened on Feb 8, 2017

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Description

Hi , I am using DSCP parameter of iperf for udp packets. I used both iperf2 and iperf3 latset version ie.iperf 3-CURRENT.

Iperf2 sets it n 3rd frame while latest iperf(iperf 3-CURRENT) sets the same in 5th frame.

a. wireshark snippet for iperf 3-CURRENT:

Frame 5: 342 bytes on wire (2736 bits), 342 bytes captured (2736 bits) Ethernet II, Src: fa:16:3e:2c:7c:9a (fa:16:3e:2c:7c:9a), Dst: AristaNe_00:00:a0 (00:1c:73:00:00:a0) Internet Protocol Version 4, Src: 96.118.224.85, Dst: 96.116.32.162 0100 .... = Version: 4 .... 0101 = Header Length: 20 bytes Differentiated Services Field: 0xb8 (DSCP: EF PHB, ECN: Not-ECT) 1011 10.. = Differentiated Services Codepoint: Expedited Forwarding (46) .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)

b. wireshark trace snippet for iperf2:

## Frame 3: 342 bytes on wire (2736 bits), 342 bytes captured (2736 bits) Ethernet II, Src: fa:16:3e:1d:36:fd (fa:16:3e:1d:36:fd), Dst: AristaNe_10:64:4c (00:1c:73:10:64:4c) Internet Protocol Version 4, Src: 96.116.32.162, Dst: 96.118.224.85 0100 .... = Version: 4 .... 0101 = Header Length: 20 bytes ## Differentiated Services Field: 0xb8 (DSCP: EF PHB, ECN: Not-ECT) 1011 10.. = Differentiated Services Codepoint: Expedited Forwarding (46) .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)

So cant we get DSCP bit in the third frame of iperf data in new iperf3 -Current.

Thanks Puru

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Tech stack
c
Domain
cliperformance
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C programmingnetwork socket programmingiperf codebase structure
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate the iperf3 source code, particularly the socket setup and option setting in `iperf api.c` or `iperf udp.c`. Compare with iperf2's approach to setting DSCP/TOS. Look for differences in when the `setsockopt` call is made (before or after connect or first send). The goal is to ensure DSCP is applied to the first packet of the data stream rather than later frames.