Hi all,
I noticed that lwIP returns an echo-reply packet with the same TTL as the received echo-request packet. Is this correct ?
I executed some tests in a local network (0 hops) pinging several types of machines with different TTLs and got the following results: - Linux box always returns echo-replies with TTL=64 - Windows 2000 box always returns echo-replies with TTL=128 - An SMSC gateway/router always returns echo-replies with TTL=255
I didn't find any comments in the RFCs about the supposed value of TTL for echo-replies.
I noticed this behaviour when I did a traceroute (through the Internet) to a server and to an embedded system running lwIP in the same network. The traceroute of the lwIP embedded system had TWO TIMES the number of hops of the server.
This happens, I think, because the icmp echo-reply packet sent by lwIP will reach the traceroute system only when the TTL of the original packet have two times the number of hops of the route. The first half is spent reaching the lwIP system and the other half is spent on the way back to traceroute system.
So, I really think that for traceroute to work OK with lwIP, the TTL of the echo-reply packet should be 64 or greater. Any comments ?
Regards, Claudio
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