ipv4 id is changed by trex (together with checksum)

[PanPaskuda]

Hi, I got strange results while sendig high rate packets, but was able to create simplest reproducible scenario:

it seems that all ids above 0xFBFF are reserved and when they appar, trex silently flip bit no 12

to reproduce: write this snippet as test.py

from trex.stl.api import *

class STLS1(object):
    def get_streams(self, direction = 0, **kwargs):
        streams = []
        packet = (Ether(dst='00:00:00:00:00:01') /·
                  IP(id=0xFFFF,chksum=0xAAAA))

        vm = STLVM()
        stream = STLStream(packet = STLPktBuilder(pkt = packet, vm = vm),
                           mac_src_override_by_pkt = True,
                           mac_dst_override_mode = 1,
                           mode = STLTXSingleBurst(total_pkts = 1, pps = 1.0))
        streams.append(stream)

        return streams

def register():
    return STLS1()

but instead of 0xFFFF as ip id, trex sends 0xEFFF (and changes checksum too to not keep them sane),
so when send by cmd: trex>start -f /path/to/test.py tcpdump shows:

11:52:55.744521 IP 16.0.0.1 > 48.0.0.1:  hopopt 0
        0x0000:  0000 0000 0001 0000 0002 0000 0800 4500  ..............E.
        0x0010:  0014 efff 0000 4000 baaa 1000 0001 3000  ......@.......0.  << here `efff` as ip id and `baaa` as chksum
        0x0020:  0001 0000 0000 0000 0000 0000 0000 0000  ................
        0x0030:  0000 0000 0000 0000 0000 0000            ............

is it bug or maybe just a hidden feature? ;) how to fix it or workaround?

 Version : v3.06                                           
 DPDK version : DPDK 24.03.0                               
 User    : hhaim                                           
 Date    : Sep  9 2024 , 14:24:11                          
 Uuid    : a548d75a-6e9d-11ef-9725-0025b5ff001d            
 Git SHA : 61fb7aead7063d98bf16cd9392e85021193d5584        
                                                           
Compiled with GCC     :   8.3.1 20190311 (Red Hat 8.3.1-3) 
Compiled with glibc   :   2.17 (host: 2.31)                
Sanitized image       :   no