Difference in address selection between ICMP and TCP

[Guido van Rooij]

Consider the following:
ifconfig em0 inet 1.2.3.4/24 
ping 1.2.3.4

Then a tcpdump on lo0 shows:
21:15:56.641571 IP 127.0.0.1 > 1.2.3.4: ICMP echo request, id 36105, seq 10, length 64
21:15:56.641582 IP 1.2.3.4 > 127.0.0.1: ICMP echo reply, id 36105, seq 10, length 64

I think that the address used should have been 1.2.3.4 and not 127.0.0.1.

Now when I do a telnet 1.2.3.4 22, I see:
21:17:55.955475 IP 1.2.3.4.38534 > 1.2.3.4.22: Flags [S], seq 904951907, win 65535, options [mss 16344,nop,wscale 3,sackOK,TS val 1850412 ecr 0], length 0
21:17:55.955487 IP 1.2.3.4.22 > 1.2.3.4.38534: Flags [R.], seq 0, ack 904951908, win 0, length 0

So in this case we actually do use 1.2.3.4!

This is on a 8.1 system. A 8.2 system shows the same behaviour and a 7.4
system behaves correctly (i.e.: uses the same address for icmp as for
tcp).

I tried to investigate the souce code, but my knwoledge about it is a
bit rusty :-(

-Guido

NB: perhaps related: When I do the ping in a vimage on a different
VIMAGE-kernel, the ping fails because the source address is never
filled in (i.e. is 0.0.0.0)