RE: Cable Vs. DSL

[Jordan Jesse - Toronto-MROC <jjordan () mroc com>]

Well, its likely that he is using a Linksys or D-link NAT enabled router,
which in that case is pretty secure because these routers are also stateful
packet filters.

So in short, yes your clients are pretty secure as long as you are not port
forwarding services internally, in which you open yourself up to whatever
vulnerabilities exist on the running internal services. If you don't have a
lot of clients, it would be a good idea to set your IP's up statically, and
filter unused IP's and MAC addresses at the router - this would help if you
had a case of IP spoofing, it would also make it a little easier in internal
log analysis.

> Since the router's address is seen as one address from outside, and
> there's no "host" at that IP address, and it is administered at an internal

> address inside the network, is there any way for an intruder to compromise 
> my network and get to any of my client machines?

There are ways, as I mentioned above, the most obvious being port forwards.
Other then that, make sure remote management is not accessible from the
outside, and make sure you are running the latest firmware. Also make sure
your WAN port is set to block unsolicited requests. If you are just a home
user, I wouldn't worry about predictable TCP ISN #'s or firewalking - unless
you specifically have someone targeting you who is very very determined. If
your router has the functionality, its generally a good idea to block all
ICMP (outbound, block ICMP Destination Unreachable).

Jesse

-----Original Message-----
From: Chris Berry [mailto:compjma () hotmail com]
Sent: Monday, April 28, 2003 10:20 PM
To: security-basics () securityfocus com
Subject: Re: Cable Vs. DSL


> From: Greg Tracy <greg () sixx com>
> Here's a question (I'm relatively new at this).

Well, you're in the right place, that's a good start.

> I have a cable connection, with a broadband NAT router which acts as a
> DHCP server for a variety of clients (Mac, Win2K and Linux). All the
> machines are given an internal IP address (like the old class C
> addresses) and the router has the address assigned by the ISP, which
> is what the clients are seen to have from the internet.

So basically what you're saying is that you have one public IP address and 
the rest are private non-publicly routable ones divided by your NAT enabled 
router.

> Since the router's address is seen as one address from outside, and
> there's no "host" at that IP address, and it is administered at an internal

> address inside the network, is there any way for an intruder to compromise 
> my network and get to any of my client machines?

In short, yes, lots of ways.

> Is this the best way (other than using a firewall, or in addition to) to 
> make this connection more secure?

NAT basically provides you with about as much security as your mp3 player, 
which is to say none at all.  This is because NAT is not designed as a 
security measure, it's merely a way to broaden the available address pool.  
Here are some basic measures I'd recommend to secure your network:

1) Firewall
2) Anti-Virus
3) Spyware detector for your windows machines (I like SpybotSD)
4) Decent passwords on your systems

Depending on your level of paranoia, there's lots more.

Chris Berry
compjma () hotmail com
Systems Administrator
JM Associates

"Without change, something sleeps inside us, and seldom awakens.  The 
sleeper must awaken." -- Duke Leto Atreides

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