What's the size of the ICMP packet payload when the type is 11, i.e. time exceeded? Since it contains an IP header and the first 8 Bytes of the IP packet payload generating the ICMP message, I thought its size was 20 + 8 = 28.
I'm replaying some common user traffic with TTL=1. In the ICMP messages I have dumped I noticed that:
- all ICMP packets generated by UDP packets have payload of size 28 Bytes
- all those generated by TCP packets have payload of size 40 Bytes
Since I need to match ICMP time-exceeded messages with the packets that triggered them by comparing those bytes, this piece of information is essential, but I can't find figure out why this happens.