[CentOS] bad udp cksum

Thu Sep 6 12:59:39 UTC 2018
Jürgen Gotteswinter <Juergen.Gotteswinter at financial.com>

Well, it is in general a good idea to disable all the fancy nic feature like tso, gro, rx/tx offload if strange things happen



-----Ursprüngliche Nachricht-----
Von: CentOS <centos-bounces at centos.org> Im Auftrag von Eliezer Croitoru
Gesendet: Donnerstag, 6. September 2018 13:51
An: 'CentOS mailing list' <centos at centos.org>
Betreff: Re: [CentOS] bad udp cksum

I have seen such and issue but it depends on the environment structure.
I have seen it mostly on VM's and it was resolved.
The hardware and software details of the setup might help to understand what's causing it.

Eliezer

----
Eliezer Croitoru
Linux System Administrator
Mobile: +972-5-28704261
Email: eliezer at ngtech.co.il


-----Original Message-----
From: CentOS [mailto:centos-bounces at centos.org] On Behalf Of Laszlo Danielisz
Sent: Thursday, August 9, 2018 9:53 PM
To: centos at centos.org
Subject: [CentOS] bad udp cksum

Hi,

Recently I'm noticing an interesting issue.
My CentOS servers are trying to send logs to a logging server via 514/udp, however I'm not receiving anything.

I did the following on CentOS
*tcpdump -vvv -nn udp -i esn160 port 514*

In another session on the same server:
*nc syslog-server -u 514*

tcpdump started to show me messages like:
*[bad udp cksum 0x3ce9 -> 0xb0f5!] SYSLOG, length: 172*

After some research I disabled TCO (ethtool -K ens160 tx off rx off), now tcpdump shows:
*[udp sum ok] [|syslog]*
And I'm also receiving the logs. Yay!

I have the same issue on multiple servers with CentOS versions 7.3.1611,
7.4.1708 & 7.5.1804. I'm having the issue no matter if it is a physical or virtual server (they also use different hardware and NIC's)

Of course I could run ethtool every time a server starts but I think there should be a better solution. Also I enjoy having TCO giving some rest to the CPUs.

Did anyone find a solution for this?

Thanks!
Laszlo
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