https://www.networkworld.com/article/2224654/cisco-subnet/mtu-size-issues.html

the GRE header is 24 bytes and an IP header is 20 bytes.

شما باید این مقادیر رو از مقدار کلی MTU کانکشن کم کنید

https://elifulkerson.com/projects/mturoute.php

1500 <-- Starting MTU
- 20 <-- Subtract 20 bytes for the IP headers (EoIP)
-  8 <-- Subtract GRE protocol header (EoIP)
- 14 <-- Subtract the encapsulated Ethernet header (sans checksum)

http://packetlife.net/blog/2008/aug/18/path-mtu-discovery

http://www.tp-link.com/us/FAQ-190.html

IP MTU and TCP MSS Missmatch – an evil for network performance

ping Ipaddress -f -l size of packet

http://blog.ipspace.net/2013/01/tcp-mss-clamping-what-is-it-and-why-do.html

      MSS = MTU – sizeof(TCPHDR) – sizeof(IPHDR)” 

MSS = MTU – 20(IP header) – 20(TCP Header) = 1460

https://stackoverflow.com/questions/22705314/how-to-calculate-mss

For MTU 1500 MSS1460

MSS (maximum segment size) typ. MTU-40B (TCP/IP header)

https://www.sonicwall.com/en-us/support/knowledge-base/170504812146650

https://www.iea-software.com/products/mtupath