If I check how many connections serverA (192.168.1.1) has open to serverB (192.168.2.1), I get the following response:
[username@serverA ~] $ netstat -n | grep 192.168.2.1
tcp 0 0 192.168.1.1:51846 192.168.2.1:10001 ESTABLISHED
tcp 0 0 192.168.1.1:50872 192.168.2.1:10001 ESTABLISHED
tcp 0 0 192.168.1.1:51824 192.168.2.1:10001 ESTABLISHED
tcp 0 0 192.168.1.1:51848 192.168.2.1:10001 ESTABLISHED
[username@serverA ~] $ netstat -n | grep 10.79.165.145 | wc -l
4
However, if I do the opposite and check on serverB how many connections it has open to serverA, I get this:
[username@serverB ~] $ netstat -n | grep 192.168.1.1
tcp 0 0 192.168.2.1:10001 192.168.1.1:51846 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:55122 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:59930 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:50352 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:44142 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:57698 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:38268 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:41822 ESTABLISHED
... many more connections ...
tcp 0 0 192.168.2.1:10001 192.168.1.1:43840 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:50870 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:34100 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:34620 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:41126 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:49298 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:50004 ESTABLISHED
tcp 0 0 192.168.2.1:10001 192.168.1.1:51408 ESTABLISHED
[username@serverB ~] $ netstat -n | grep 192.168.1.1 | wc -l
104
I was not expecting there to be a mismatch in the number of the connections between the 2 servers, essentially serverB thinks there are a lot more connections open to serverA and than that serverA does to serverB.
These servers are on different VLANs and the connections do go through a firewall. Both serverA and serverB are RHEL v7 VMs running on ESXI. They don't run any containers or anything that would do NAT.
What could be responsible for the mismatch in open connection numbers
