[CentOS] bad udp cksum

Thu Sep 6 11:51:29 UTC 2018
Eliezer Croitoru <eliezer at ngtech.co.il>

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 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
Sent: Thursday, August 9, 2018 9:53 PM
To: centos at centos.org
Subject: [CentOS] bad udp cksum


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?

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