Re: dual IP

[Brian Candler <B.Candler@pobox.com>]

On Sat, May 19, 2001 at 06:56:53AM +0530, mpradhan@healthnet.org.np wrote:
> I am using both Public IP 202.52.231.194 and Private IP 
> 192.168.0.1.  In the Private I can ping but cannot telnet as well as  
> ping to port 25 i.e ping  192.168.0.1 25 and  to port 110 i.e. ping 
> 192.168.0.1. Earlier I could do telnet as well as ping to port 25 and 
> 110 through private IP.

I think you are getting a little confused.

'ping' sends an ICMP echo-request and the far end returns an ICMP
echo-response. There is no port number involved. Port numbers apply to TCP
and UDP only. So "ping 192.168.0.1 25" is meaningless. In fact, on my Linux
laptop, that makes it try to ping 0.0.0.25 (which is a non-existent IP
address and of course fails). On FreeBSD it gives a syntax error.

So the valid things to try are:

- ping 192.168.0.1           (can I send ICMP echo-request to this address
                              and get an ICMP echo-response back?)

- telnet 192.168.0.1 25      (can I connect to TCP port 25 on this machine,
                              i.e. the SMTP daemon?)

Regards,

Brian.