MTU

on

Change Window  NIC 


 1.Show current MTU size


netsh interface ipv4 show subinterfaces

2. Run commands

netsh
interface
ipv4

set subinterface “Ethernet0” mtu=1400 store=persistent



===============

MTU 1500 is IP packet size, doens't include Ethernet Header (14 bytes), either Frame check sequence (FCS) (4bytes)

Wireshark capture Length column is MTU + Ethernet Header (14 bytes) = 1514

ASA packet capture by default is 1518.


ping -f 192.168.2.1 -l 1472

1472 + 8 byes ICMP Header + 20 bytes IP Header = 1500, in Wireshark capture, Length is 1514.

C:\Users\jliu>ping -f 192.168.2.1 -l 1473

Pinging 192.168.2.1 with 1473 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.

Ping statistics for 192.168.2.1:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

C:\Users\jliu>ping -f 192.168.2.1 -l 1472

Pinging 192.168.2.1 with 1472 bytes of data:
Reply from 192.168.2.1: bytes=1472 time=4ms TTL=64
Reply from 192.168.2.1: bytes=1472 time=4ms TTL=64
Reply from 192.168.2.1: bytes=1472 time=4ms TTL=64
Reply from 192.168.2.1: bytes=1472 time=6ms TTL=64

Ping statistics for 192.168.2.1:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 4ms, Maximum = 6ms, Average = 4ms


https://www.dasblinkenlichten.com/the-basics-mtu-mss-gre-and-pmtu/

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