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Re: Nortel Contivity 2600
From: Rodrigo Blanco <rodrigo.blanco.r () gmail com>
Date: Thu, 8 Sep 2005 12:00:11 -0600

I would still put the outside interface of the VPN device behind an in-line IPS
box, otherwise you could still be vulnerable to DoS attacks (IKE
flooding...) against the VPN device itself.

However I completely agree to keep things as simple as possible.

Regards,
Rodrigo.

On 9/8/05, Kyle Starkey <kstarkey () siegeworks com> wrote:
So I understand the concerns and I think the best way to do this for both
simplicity and security is a combination of things that have been suggested.

1) Put the outside interface of the 2600 on border net (outside the FW) and
pin up some ACL's on the border router as Dario has suggested.  This will
keep all but encrytion traffic getting to your VPN device.

2) Put the inside interface in a DMZ of its own with an IPS device between
the inside vpn int and the DMZ interface.  This will allow you to monitor
and shutdown traffic based on sig's in the IPS, but will also allow you to
rate limit traffic from the VPN and create ACL's for new worm traffic before
your IPS vendor gets around to creating a sig for it.

3) Limit traffic on the DMZ interface from the VPN source IP only to items
that are absolutely necessary.  If possible segment different types of users
into different source IP space so that the ACL's on the DMZ FW can be group
specific (ie general users get access to the mail server and file share,
where as security and networking teams aditionally have SSH access to a hop
point in the network, HR has access to their DB, sales has access to the
CRM, etc)

Trust me... After implementing dozens of different VPN solutions over the
years you are better off to NOT complicate the IPSEC connection by trying to
put NAT on both the client and server end of the tunnel... You will end up
tearing your hair out trying to make sure that the vendors have implemented
the proper RFC's to make sure that is supported... And don't even get me
started on NAT-T...

-Kyle

-----Original Message-----
From: Dario Ciccarone (dciccaro) [mailto:dciccaro () cisco com]
Sent: Tuesday, September 06, 2005 3:14 PM
To: misiu; pen-test () securityfocus com
Subject: RE: Nortel Contivity 2600


For the 'why NAT and IPSec don't play nice together' question, go check
http://www.ietf.org/rfc/rfc3715.txt - and after reading that, check for
IPSec NAT-T (rfc-editor being a good place to start)

You mention deploying the VPN box behind an IPS device. Yes and no. What
are you trying to achieve? If your IPS box is inline, and does protocol
checking/normalization, that could work - the IPS would drop the
malformed packets and notify the management console (possibly). But do
you need/want to have that information?

Before deciding where to connect the VPN device (firewall, inline IPS,
nothing) we should decide what we want to achieve by doing it.

And there have been some comments about the VPN box interaction with
NAT. Deploying it behind a firewall != NATting - either because you
configure a 1:1 translation between public IP/private IP, or you use an
L2-firewall.



-----Original Message-----
From: misiu [mailto:misiu_ () gmx de]
Sent: Tuesday, September 06, 2005 5:14 AM
To: pen-test () securityfocus com
Subject: Re: Nortel Contivity 2600

Dario Ciccarone (dciccaro) schrieb:
Putting the device in question behind the firewall isn't
going to help
him with DoS attacks - unless those attacks are due to malformed
packets, _and_ the firewall in question drops the type of malformed
packets that would trigger the DoS.


Hmm, but if malformed packs come, is it not much better to
set it behind
  an IPS? Firewall is not allways the right thing to protect, i guess.
I don't really understand why Nat is not working....
The Adresses of the tunnel are not encrypted, do they might have a
checksum wich is altered through a NAT device?

Do I see this right?

misiu

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