Strange (newbie) Gateway Errors

Chuck Swiger cswiger at mac.com
Sat Sep 10 09:23:30 PDT 2005


Thomas Dimson wrote:
> I don't have natd configured in the slightest. My assumption was that I 
> didn't need to run it because I have a router assigning the IP addresses and 
> doing NAT for my cable modem, while my university is assigning me an IP 
> address for the second interface. Maybe I do need to run it. Can someone 
> point me in the direction of an install guide, or quickly explain it - the 
> man page confused me half to death.
> 
> Also: what was that information about having natd on both interfaces? I know 
> that's nonstandard, so how would you configure that?

It's likely that setting up a route for the university subnet on the client 
machines, via routed, or on your routers which points to your university-bound 
interface would help.

At one point, when I was going some experimentation with sendmail, I got a call 
from the senior admin at CMU, who asked for me by name and immediately asked me 
to pull my ethernet cable out of my computer because it was generating about 50 
bounces a second to <postmaster at cmu.edu> in a mailing loop.

I mention this because if you enable natd in both directions, you are probably 
going to loop university traffic out your cable connection, and vice-versa for 
Internet traffic in via your university's network, bypassing their firewalls 
and security in the process.

Before you get a call from some senior admin who is not going to be thrilled to 
solve an emergency on a Saturday, I suggest you stop for a second, figure out 
what you actually need or want to do, and be prepared to discuss it with your 
university admins beforehand and get their advice.

-- 
-Chuck



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