Re: [fw-wiz] separating the servers on a switch

From: m p (sumirati@yahoo.de)
Date: 09/12/02


From: m p <sumirati@yahoo.de>
To: Shimon Silberschlag <shimons@bll.co.il>
Date: Thu Sep 12 15:25:02 2002


[ Sorry, i hit send too fast. I'm resending it full :)]

 --- Shimon Silberschlag <shimons@bll.co.il> schrieb: > The servers need to
talk with the uplink (internet) servers, the
> downlink (backend) servers. This is trivially done with the firewalls.
> What we want to do is control which servers on the segment talk among
> themselves.
>
> Shimon Silberschlag

The only way to solve the problem I can think of is to install more firewalls /
paketfilters and give each server a seperate interface on that firewall. It
would look like this ( in good old ASCII art):

            Internet
                |
                |
    screening router / Firewall (already in place)
                |
                |
Public DMZ Firewall - Server 1
                | | |__ Server 2
                | |____ Server 3
                |
                |
    screening router / Firewall (already in place)
                |
                |
Private DMZ Firewall - Server 1
                  | |__ Server 2
                  |____ Server 3
             

VLANs are not secure. You may circumvent them. Even if you define VLANs - how
do you control the traffic in them?

The smoothest way to do that is from my point of view to install *BSD (or if
you are more familiar the word with L.... ;), put them into bridging mode and
install a kind of paket filter (perhaps with a self-train phase) upon them. Put
a managment link with an IP into them. Voila.
Your mileage may vary.

The plus is that you don't have to go into subnetting your IP range into
smaller pieces, put load down from the main firewalls, if you don't change the
TTL or other headers there is virtually no way to detect them.
The downside is that you add a layer of comlexity and single point of failure.

Just my 2 cent.

Marc

> ----- Original Message -----
> From: "m p" <sumirati@yahoo.de>
> To: "Shimon Silberschlag" <shimons@bll.co.il>
> Sent: Thursday, September 12, 2002 15:56
> Subject: Re: [fw-wiz] separating the servers on a switch
>
>
> > Hi Shimon,
> >
> > please decompress your question && resend it.
> >
> > thanks
> >
> > marc
> >
> > ps: look for the comment.
> >
> > --- Shimon Silberschlag <shimons@bll.co.il> schrieb: > Lets say we
> have an
> > internet segment, protected by firewalls at both
> > > ends. On that segment are various servers.
> > > The servers need to talk to other servers outside the segment;
> uplink
> > > its the internet, downlink the backend servers.
> > > Some of the servers need to be able to talk among them.
> >
> > ^-- from here on it is not clear which servers are which servers are
> on which
> > link they are.
> >
> > > We want to control which server can talk to which other server (in
> the
> > > segment), utilizing one of the firewalls (lets say the uplink
> one).
> > > Can the group suggest ways to accomplish that? We thought about
> using
> > > L2 switches with "private VLAN", L3 switches with ACL, but
> constantly
> > > come across problems doing the routing properly.
> > >

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