[CentOS] Centos 7: UPD packet checksum verification?

Tue Jan 28 08:00:22 UTC 2020
Nataraj <incoming-centos at rjl.com>

On 1/26/20 5:44 PM, hw wrote:
> On Sunday, January 26, 2020 11:18:36 PM CET Pete Biggs wrote:
>> First of all - disclaimer - I'm no network specialist, I just read and
>> am interested in it.  I may get things wrong!!
>>> Both physical interfaces show the same.  But does this mean it's on as in
>>> "rx- checksumming: on" or off as in "tx-checksum-ipv4: off [fixed]"?
>> As far as I understand it rx-checksum is the underlying wire
>> checksumming - and from what I've read about it, disabling that
>> disables the UDP checksums.
> You mean layer 1 checksumming?  Is there such a thing with ethernet?  I think 
> I read something about encoding, when I was trying to understand what 
> "bandwidth" actually means, being involved in signal transmissions; and I seem 
> to remember that there was no checksumming involved and it had to do with 
> identifying signals as a requirement for the very possibility to transmit 
> something before anything could be transmitted at all.
>>> Assuming that I do not receive packets with invalid UPD checksums, then
>>> the
>>> packages must be somehow altered and their UPD checksums recalculated to
>>> arrive here.  Does bad hardware etc. do that?  Why would the UDP checksums
>>> just happen to get recalculated correctly but like randomly without
>>> intent?
>> I'm not sure I understand what you are asking.
> It is about VOIP calls via SRTP being interrupted at irregular intervals.  The 
> intervals appear to depend on the time of day:  Such phone calls can last for 
> a duration of about 5--25 minutes during the day to up to 1.5 hours at around 
> 3am before being interrupted.

My sense is you may be starting at too low of a level in trying to debug
this.  I have seen the same kind of problems with my voip service when
there is a problem with my Internet connection.  When this happens I
also see high retransmission rates for tcp connections and other signs
of network problem.  If I check the modem for my Internet connection
there are issues with the signal levels and high error rates reported by
the modem.  If you believe your Internet connection is reliable, then if
you run managed switches, check your switch logs for any reported errors.

You could try tools like iperf to check for problems on your internal
network.  You could run some of the basic tools for testing voip
performance of your Inetnet connection and if necessary run iperf to a
cloud hosted system.

I think it is highly unlikely that you are only having issues with srtp
packets and I would look at the broader picture first to try to isolate
some other problem in your network or Internet connection.