Fix MTU problems..

MTU_improvements.txt

### Ping tool

## LINUX ##
#prohibit fragmentation even local one
 ping -s 1462 -M do 195.175.39.49
 
#do PMTU discovery, fragment locally when packet size is large
 ping -s 1472 -M want 195.175.39.49
 
========================================= 
 ## FreeBSD TCP improvements ##
 https://freebsdfoundation.org/wp-content/uploads/2016/10/TCP-Improvements-in-FreeBSD.pdf
 
 ### Path MTU Discovery for Blackhole Detection ###
 
#Use the following sysctls to configure this feature:

```
net.inet.tcp.pmtud_blackhole_detection - Enable/Disable
net.inet.tcp.pmtud_blackhole_mss - Lowered MSS for IPv4
net.inet.tcp.v6pmtud_blackhole_mss - Lowered MSS for IPv6
```

#Use the following sysctls to monitor this feature:

net.inet.tcp.pmtud_blackhole_activated - How many times we detected a blackhole and activated MSS down-probing.
net.inet.tcp.pmtud_blackhole_activated_min_mss - How many times we detected a blackhole and went down to minimum MSS configured during MSS down-probing.
net.inet.tcp.pmtud_blackhole_failed - How many times we detected a blackhole incorrectly

SOURCES:

#When To Use Adjust MSS
https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000PN0gCAG
https://www.javatpoint.com/what-is-mss