[Network] Main ICMP Error Messages

□ ICMP Error message : The error messages are separated by "Type" and "Code"

○ Destination Unreachable

- Type 3
- Packet can't reach the destination
- There are 16 different unreachable detailed reason(=Code)

ㆍCode 0 : There is no path that can go to the destination
ㆍCode 1 : A result of the check, the destination host does not exist
ㆍCode 15 : The packet could not be reached because the priority pressed

○ Time Exceeded

- Error Type : Type 11
- The data is discarded because the TTL value was zero
- Because of the packet recombination and other tasks, the time is exceeded, the data is repealed

□ TIP : While the host does not exist, error message Type 11 : Until the TTL value reaches zero, The packet is wandering network.