Hi, When I send UDP packet (too big for whole path) and close socket right after, ICMP Fragmentation Needed packet is ignored (?) and no entry regarding path MTU is created. When process waits before closing socket (about 1s in my case) entry about path MTU is added to routing table. The result is that when I send single big (bigger than minimal MTU in path) UDP packet very rarely none of them reaches destination. When there is continuous stream of packets and there is always open socket for this destination IP everything (regarding path MTU discovery mechanism) works as expected.
Is there any way to change this behaviour? Or is this some kind of DDoS protection mechanism? I am aware of timeout of table MTU entries but "very rarely" in my case means more often than timeout value. Environment: - Ubuntu 14.04.5 LTS, kernel 4.4.0-104-generic #127~14.04.1-Ubuntu - Intel(R) 2P X520/2P I350 rNDC | Intel Corporation 82599ES 10-Gigabit, driver=ixgbe driverversion=4.2.1-k, 18.3.6 (firmware driver from Dell) Code used for testing and my network architecture: - https://pastebin.com/raw/ECY3Xxtg - https://i.imgur.com/T7SpDyP.png -- Oskar Jagodzinski