Are TCP/UDP IP packets with a source port below 1024 possible - tcp

Question

I am analyzing some events against dns servers running unbound. In the course of this investigation I am running into traffic involving queries to the dns servers that are reported as having in some cases a source port between 1 and 1024. As far as my knowledge goes these are reserved for services so there should never be traffic originating / initiated from those to a server.
Since I also know this is a practice, not a law, that evolved over time, I know there is no technical limitation to put any number in the source port field of a packet. So my conclusion would be that these queries were generated by some tool in which the source port is filled with a random value (the frequency is about evenly divided over 0-65535, except for a peak around 32768) and that this is a deliberate attack.
Can someone confirm/deny the source port theory and vindicate my conclusion or declare me a total idiot and explain why?
Thanks in advance.
Edit 1: adding more precise info to settle some disputes below that arose due to my incomplete reporting.
It's definitely not a port scan. It was traffic arriving on port 53 UDP and unbound accepted it apparently as an (almost) valid dns query, while generating the following error messages for each packet:
notice: remote address is <ipaddress> port <sourceport>
notice: sendmsg failed: Invalid argument
$ cat raw_daemonlog.txt | egrep -c 'notice: remote address is'
256497
$ cat raw_daemonlog.txt | egrep 'notice: remote address is' | awk '{printf("%s\n",$NF)}' | sort -n | uniq -c > sourceportswithfrequency.txt
$ cat sourceportswithfrequency.txt | wc -l
56438
So 256497 messages, 56438 unique source ports used
$ cat sourceportswithfrequency.txt | head
5 4
3 5
5 6
So the lowest source port seen was 4 which was used 5 times
$ cat sourceportswithfrequency.txt | tail
8 65524
2 65525
14 65526
1 65527
2 65528
4 65529
3 65530
3 65531
3 65532
4 65534
So the highest source port seen was 65534 and it was used 4 times.
$ cat sourceportswithfrequency.txt | sort -n | tail -n 25
55 32786
58 35850
60 32781
61 32785
66 32788
68 32793
71 32784
73 32783
88 32780
90 32791
91 32778
116 2050
123 32779
125 37637
129 7077
138 32774
160 32777
160 57349
162 32776
169 32775
349 32772
361 32773
465 32769
798 32771
1833 32768
So the peak around 32768 is real.
My original question still stands: does this traffic pattern suggest an attack or is there an logical explanation for, for instance, the traffic with source ports < 1024?

Answer 1

As far as my knowledge goes these are reserved for services so there should never be traffic originating / initiated from those to a server.
It doesn't matter what the source port number is, as long as it's between 1 and 65,535. It's not like a source port of 53 means that there is a DNS server listening on the source machine.
The source port is just there to allow multiple connections / in-flight datagrams from one machine to another machine on the same destination port.
See also Wiki: Ephemeral port:
The Internet Assigned Numbers Authority (IANA) suggests the range 49152 to 65535 [...] for dynamic or private ports.[1]

Answer 2

That sounds like a port scan.
There are 65536 distinct and usable port numbers. (ibid.)
FYI: The TCP and UDP port 32768 is registered and used by IBM FileNet TMS.