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== 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. 

== frag needed ==
 [[attachment: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。

== 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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