We have a vm centos 5.x in a vmware infra that works fine.
It has 2 nics and some traffic coming from outside to one of the nic's ip on port UDP 514 and 516.
I see with tcpdump the traffic coming to the ip/port and netcat shows me that the ip and port receive the packet (those are syslog messages so I can see them).
We wanted to upgrade the VM to Centos 7.1. Same Nic, same IP, no much more hardening, pretty simple.
So we create a new Centos 7.1 vm, same vmware network, same esx.
Now, I still can see the traffic coming from outside the vm to the Nic's ip and port but a netcat on udp 516 shows nothing at all. On udp 514 it works. And I use the exact same commands.
No iptables or selinux.
I use the exact same tcpdump or netcat commands on both vms to do my tests.
If I switch to the old Centos 5 vm, then everything is back to normal: tcpdump show trafic on udp 514 and 516, netcat of udp 514 and 516 show the messages.
This thing driving crazy because I don't see any logical reaason for this. I will test with a vanilla Centos 7.2 but in the meantime I am wondering if someone somewhere in this universe already have this kind of issue.
Thanks for your help!