switches in a fw environment

[Gerhard Mezger <Gerhard.Mezger () mail inuco ch>]

How do you feel about the usage of switches interconnecting different
security domains? To illustrate my question let's take a look at a
very
simplified Internet connection:


              PR   -----------  Firewall --------- internal net (S)
                                   !
                                   !
                                  WEB

PR=Provider Router;  WEB=Webserver in DMZ;   S=System in the internal
net (running critical appliacations).

Internet users are only allowed to access the Webserver; access from
the

internal net to the Internet is very restricted. So far the logical
layout. Letns now look at a possible physical implementation using
VLANs:


                             Firewall
                               !  !  !  vlans 1 2 3
                            +---------+
               PR---------- !  Switch !-----------S
             vlan1          +---------+  vlan3
                                  !
                            vlan2 !
                                  !
                                WEB

I am not sure about the security risk imposed by a central switch
especially because the management of the switch will be done over a
(separate) VLAN. I am searching for arguments to become either more
comfortable with this solution or to have strong technical arguments
against it.

Your input is highly appreciated
Gerhard