On 31.01.2012 21:27, Guido van Rooij wrote:
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 :-(
The way the source address is determined is different between ping-icmp and TCP. For ping-icmp the source address is filled in ip_output() based on the outgoing interface. For all local addresses, including those on real interfaces the loopback interface is used. You can see that by doing a "netstat -ran".
-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)
The loopback interface is inaccessible from a jail and thus the source address is never filled in and stays at INADDR_ANY. A fix for either issue is not entirely trivial and fraught with other potential undesired side effects. -- Andre _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
