Bug 1040

Overview Description:
Doing port forwarding from localhost to another host only works if the IPv4 address is 127.0.0.1.  It 
should work for anything in 127/8.  (Have not tested IPv6)

Steps to reproduce:
1) verify that 127.0.0.2 is indeed a valid localhost address on the host in question.  For Debian "Sarge" 
it is; for Mac OS X you need to ifconfig lo0 .... alias.  But once you have, connect to 127.0.0.2:running-
service to verify that the host believes that 127.0.0.2 is a valid IPV4 address for loopback
2) Start an ssh port forwarded tunnel.  For me, that's:

ssh -L 2426:mail.fsf.net:25 -N adam@mail.fsf.net

3) connect to the forwarded port at 127.0.0.1.  For me, 

telnet 127.0.0.1 2426
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
220 services.fsf.net ESMTP Exim 4.50 Thu, 12 May 2005 13:49:14 -0500

4) attempt to connect to the forwarded port at 127.0.0.2

Trying 127.0.0.2...
telnet: Unable to connect to remote host: Connection refused


5) kill the port forwarded tunnel and attempt to make it bind on 127.0.0.2:

sysmon:~# ssh -L 2426:mail.fsf.net:25 -N -b 127.0.0.2 adam@mail.fsf.net
ssh: connect to host mail.fsf.net port 22: Invalid argument

(that's the Debian Sarge error message, which OpenSSH_3.8.1p1 Debian-8.sarge.4, OpenSSL 0.9.7e 25 
Oct 2004; from Mac OS X, the message is: 

imac-g5-wired:~ adam$ ssh -L 2426:mail.fsf.net:25 -N -b 127.0.0.2 adam@mail.fsf.net
ssh: connect to host mail.fsf.net port 22: Network is unreachable

(in this case, the error is just flat wrong:
imac-g5-wired:~ adam$ ping 127.0.0.2
PING 127.0.0.2 (127.0.0.2): 56 data bytes
64 bytes from 127.0.0.2: icmp_seq=0 ttl=64 time=0.080 ms
^C
--- 127.0.0.2 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.080/0.080/0.080/0.000 ms
imac-g5-wired:~ adam$ ping mail.fsf.net
PING services.fsf.net (192.168.1.3): 56 data bytes
64 bytes from 192.168.1.3: icmp_seq=0 ttl=64 time=0.432 ms
64 bytes from 192.168.1.3: icmp_seq=1 ttl=64 time=0.271 ms
^C
)

Actual Results:
I could not connect to the local port 127.0.0.2 as a forwarded port.

Expected Results:
ssh should have forwarded 127.0.0.2:2426 just as it did 127.0.0.1:2426

Build date and platform:
OpenSSH_3.8.1p1, OpenSSL 0.9.7b 10 Apr 2003, Mac OS X 10.4, G5 PPC

Additional Builds and platforms:
OpenSSH_3.8.1p1 Debian-8.sarge.4, OpenSSL 0.9.7e 25 Oct 2004, Debian "Sarge" ix86

Additional Information:
The reason this matters is as a workaround for a Mail.app bug: Mail.app does not allow multiple 
outbound SMTP servers on the same host at different ports.  Since I, anal-retentively, want my 
outbound mail server to reflect the From: and Reply-To: on the mail messages I send, and since at least 
two of the three SMTP servers I use do not do SMTP auth but instead simply forward from addresses 
inside their own domains, I therefore need to ssh tunnel to a machine on which I have shell access 
inside those domains and forward a port to the SMTP server's port 25 from there.  Since Mail.app will 
not allow me to configure localhost:242[567] as different outbound servers, I need to configure them as 
127.0.0.1:2425, 127.0.0.2:2426, and 127.0.0.3:2427.  This SSH bug means that I cannot do that 
either.

Adam Thornton