raspberry pi

add a second fixed IP address:

go to /etc/network/interfaces.d/ and add a new file “eth0-secondIP” with this content:

auto eth0:1
allow-hotplug eth0:1
iface eth0:1 inet static
    vlan-raw-device eth0
    address 192.168.1.101
    netmask 255.255.255.0
    gateway 192.168.1.1

disable the wifi interface:

go to /boot and add this line to the config.txt file:

dtoverlay=disable-wifi

list network connections

netstat -na |awk '{print $5}' |cut -d "." -f1,2,3,4 |sort |uniq -c |sort -nr

ss -4 |awk '{print $6}' |cut -d "." -f1,2,3,4 |sort |uniq -c |sort -nr

These lines both returns all the connections open on the server and the destination:port.
On a proxy, it returns all the connections open towards the back-ends.

nagios manual check

[root@wfprommonp12 plugins]# /usr/lib64/nagios/plugins/check_http -H qa.comet.wfp.org -p 443 -u /implementation/login\#/ -s performance --sni --ssl  
HTTP CRITICAL: HTTP/1.1 400 Bad Request - string 'performance' not found on 'https://qa.comet.wfp.org:443/implementation/login#/' - 540 bytes in 0.221 second response time |time=0.220902s;;;0.000000 size=540B;;;0