Internet Control Message Protocol (ICMP)
- diagnostic and error reports
- ping uses ICMP
- can help to divide and conquer, if ping works it shouldn’t be a network issue => higher layer
- but it’s not that easy, pings are often blocked or dropped
ICMP type 3 codes
- 3/0
- …
- 3/3 port unreachable: can hint at software issue
- 3/13:
Communication administratively filteredhints at firewall block