ICMP
- Layer 4 protocol
- Diagnostics
- No Port numbers
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- Metadata
- Layer 2
- Layer 3
- Layer 4 (ICMP)
- Every packet that you ever sent has an IP ID, is like a serial number for packets.
- Not something that most people keep track off but can be handy in troubleshooting
- Time to Live main purpose is so that the packet does not live forever
- Happens hop by hop by hop.
- If there are no hops left, instead of forwarding, it throws this packet and returns an ICMP message that outputs ERROR.
ICMP's Protocol Number
- 1 is the protocol number for ICMP
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ICMP
- Layer 4 header being carried by a Layer 3 header
- Type 8: ("Hey are you there?")
- Looking at the ICMP you can tell who is a Linux host, Windows host etc
- There is all these atributes, different operative systems use different defaults and we can infere what type of host we are communicating with.
- If you do a PIN your computer is generating a Type 8 Echo request and if the pin is responded it returns a Type 0 Echo request.
- You can look for ICMP codes here