Re: HELP: Linux telnet smtp server fails, Works from MS Windows
From: Gonzo (gamazono_at_yahoo.com)
Date: 07/24/03
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Date: 24 Jul 2003 13:26:05 -0700
Peter, first I would like to say that I do appreciate your attempt to
help. However your tone leaves a lot to be desired. There's really no
reason to talk down to people asking questions. Many intelligent
people have been known to ask questions. Questions further ones grasp
of the world around them.
"Peter T. Breuer" <ptb@oboe.it.uc3m.es> wrote in message news:<ombmfb.sk.ln@news.it.uc3m.es>...
[much snipped, see thread]
>
> At the firewall. But please PAY ATTENTION to what I say. The
> indication is that the oruter is firewalling or not doing NAT for you.
I'm paying quite a bit of attention, thank you.
The router/firewall is not blocking port 25, and it IS doing NAT. I've
mentioned this all before.
I tend to think it's a linux issue (thus the reason for posting to
comp.os.linux.setup) because I have another computer (a windows box)
on the SAME network and that computer has no problem telneting to port
25 of the ISPs smtp server.
The linux box can PING the smtp server. PING doesn't work over port 25
so it's quite obvious that ping doesn't talk to the smtp server on
port 25. That's a given. The point is that the linux box *can* see the
smtp server, it just cannot talk to port 25 of that server. That is a
critical thing. If the linux box couldn't ping the server, I would
have to look in a different direction for the answer.
The linux box can also telnet out to many many boxes. AND it can
telnet to port 25 on other smtp servers. Those "other" servers that
can telneted to can not be used because they don't do relays (only
mail within the domain).
So bottom line is I'm pretty sure that it's something in my linux
setup. And I'm starting to think it something about the way I have my
liunx host name/domain name configured.
>
> > Since it works from a windows box on the same LAN, it's *not* the
> > wireless router (or it's firewall).
>
> Nonsense. What kind of misbegotten thinking causes you that brainfart?
> The windows box has gotten its IP by dhcp, so will certainly have had a
> hole in the firewall opened for it by the router. Something stopping
> you looking at the routers firewall?
Getting an IP address from dhcp does NOT open holes in your firewall.
That would be a bad thing. DHCP is not magical. It's simply a method
of providing IP addresses (and a few other setup things) to a host. It
doesn't do any further magic on behalf of the host.
As mentioned, I've looked at the firewall built into my router. It's
not there. That firewall lets the traffic pass. I can get to port 25
from the windows box. And I can get to other servers port 25 from my
linux box, just not the one I need to get to.
[more deleted...]
>
> The cable modem will normally have a WAN address and a localnet
> address and will be the router between yoru intranet and your ISPs
> intranet.
[stuff deleted]
> What you are saying is that the cable modem is a hub and the wireless
> station is the router. That the cable modem is not a router is nigh on
> incredible. Maybe they exist. I've not seen one. I can imagine one - it
> would be a terminal device, essentially, an extension of your isp's
> net.
>
> It normally would if you configured it to do so. As I said, it normally
> does NAT translation from an intranet. A more convenient way to set it
> up is as a port forwarder, however, for a chosen machine on your
> intranet. That machine then acts as your gateway.
This cable modem issue is a little off topic, but since we got here I
would like to help you to understand them a little more.
The cable modem does NOT do routing. One could not take a computer
with say a 192.168.x.x IP address, set it up to use the cable modems
IP address as the gateway and expect the traffic to be routed between
the two networks.
I admit, I am not an expert on HOW they work but they seem to be
bridges. Meaning IP addresses on *both* sides of the device are on the
same network. They don't route. They don't do NAT. They seem to just
bridge traffic at the MAC layer.
So, if one wants to set up an internal network, and have that network
communicate with the ISPs network, one would need a router on the
inside of the cable modem to route traffic from the internal network
to the ISP's network. NAT is needed because on my internal network,
I've decided to use 192.168.x.x addresses which are reserved (for
situations just like mine) and are not routable IP addresses. So for
my 192.168.x.x traffic to go out over the internet, NAT is needed to
make it seem like that traffic came from a routable IP address.
If you'd like to know more about the subject of cable modems you can
read about them here:
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