As for ephemeral ports:
The Internet Assigned Numbers Authority (IANA) suggests the range
49152 to 65535 (215+214 to 216−1) for dynamic or private ports. Many
Linux kernels use the port range 32768 to 61000
Looking at the destination on the TCP/IP tuple as in the example you ask:
udp 0 0 192.168.1.25:41136 188.8.131.52:123
You can see it is the current machine using an NTP service UDP/123 on a remote server.
Or else, it is your machine doing an NTP request to an NTP server in China.
Actually, all those 4 lines are connections to NTP servers in China.
Usually, with the majority of protocols, when the known port service is on your side (first), you usually are the server receiving the connection, and the ephemeral port is on the right side; when it is the contrary, often it is your server that is using a remote service.
(Is your server in China? If not I would worry about possible malware)
You can also take the out
-n, for resolving IP addresses/DNS and service names, however be aware that it introduces a noticeable lag in a machine/server with many connections (and/or with a slow DNS service). To have a feel of the difference try, I adapted your original
netstat output for a possible output without
$netstat -a | grep ESTABLISHED
udp 0 0 mylinux:41136 vns1.hinet.net:ntp ESTABLISHED
udp 0 0 mylinux:59141 DNS1.SYNET.EDU.CN:ntp ESTABLISHED
udp 0 0 mylinux:53680 rdns1.alidns.com:ntp ESTABLISHED
udp 0 0 mylinux:34255 ns1.htudns.com:ntp ESTABLISHED