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I have a vendor that is sending multicast messages using port 40000. When I watch the traffic using tcpdump the port is reporting as safetynetp as can be seen below. The application that is listening for the traffic on 40000 never receives the messages.

Is this a port conflict that would cause the messages to not be delivered to the application listening for the messages or should everything still work with safetynetp using that port?

The tcp dump traffic looks like 

09:16:16.565887 IP x.x.x.x.33957 > x.x.x.x.safetynetp: UDP, length 263
09:16:16.569960 IP x.x.x.x.57385 > x.x.x.x.safetynetp: UDP, length 263
09:16:17.225545 IP x.x.x.x.39261 > x.x.x.x.safetynetp: UDP, length 50

This is on a server running RHEL 7. Is there a way to allow the application to receive these messages?

Joe W
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1 Answers1

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It seems unlikely that this will be a port conflict. The tcpdump utility is simply reading the port name from the /etc/services file, see services(5) for more info. The /etc/service file maps a name to a port/protocol e.g.

safetynetp 40000/tcp # SafetyNET p
safetynetp 40000/udp # SafetyNET p

Unless you have taken actions to allow a connection on port 40000/udp then the default CentOS 7 firewall configuration will be blocking the connection. You should open the port in your filewall.

user9517
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  • So you would expect no interference with an application listening for those messages on 40000? – Joe W Jan 20 '17 at 15:30
  • Also the firewall explicitly allows the traffic. We're seeing the packets on the server but they don't arrive at the application. – Joe W Jan 20 '17 at 15:49