1. ping

https://changineer.info/network/cisco_ios/cisco_ios_security/cisco_ios_security_icmp.html

https://milestone-of-se.nesuke.com/nw-basic/ip/icmp/

Echo Request (Type 8) / Echo Reply (Type 0)

指定した宛先 IP まで到達できない場合
Destination Unreachable (Type 3)

【Destination Unreachable】は Network Unreachable (code 0) や Host Unreachable (code 1) など、詳細原因毎に個別の Code を持っています。

port-unreach (Port Unreachable) desired port is unreacheable to destination host.

2. frag needed

• FEfLrbpVkAUj5fs.png

Path MTU Discovery http://ipnetwork.web.fc2.com/pmtud.html

DF on で送る: ICMPのタイプOx03/コードOx04 (Destination Unreachable/Fragmentation needed and Don't Fragment was set)

破棄される原因となったMTU値(Next-Hop MTU)が含まれています。

3. Linux icmpush

icmpush - ICMP packet builder

- We want to send a packet ICMP Source Quench to host ldg02.hell 
in response to a packet destinated to host ldg00 with UDP protocol,
 source port 100 and destination port 200. We mask ourselves as gateway 10.10.10.1:

icmpush -sq -sp 10.10.10.1 -prot udp -psrc 100 -pdst 200 -orig ldg00 ldg02.hell 

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