Front cover - IBM Redbooks

148 Lotus Security Handbook
One final point regarding Figure 4-8: the firewalls and depicted connections are
not meant to imply that one zone cannot connect to another non-adjacent zone.
For example, a workstation in the Intranet zone is going to be permitted in our
model to connect “directly” to the Internet zone (or the Proxy zone). It does show,
however, that this type of connection will need to traverse multiple firewall
routers.
Now that we have shown the logical inter-zone connections and firewalls, we can
put this together with our physical representation of the firewall routers to depict
the physical inter-zone connections. We only show the physical router
connections; a more detailed physical diagram would include the switches and
hubs used for the actual NIC connections. In Figure 4-9, we show a single series
of routers. In actual practice, redundant firewall routers would be preferred as this
is a widely accepted best practice.
ISP router
Firewall (filtering router)
Firewall (filtering router)
Firewall (filtering router)
Proxy Zone
Host
Public IP
Public-facing IP
Proxy Zone
Host
Data Access 1 IP
Data Access Zone 1
Data Access
Zone Host
Proxy Zone IP
Data Access
Zone Host
Intranet IP
Internet Zone
Proxy Zone
Host
Data Access Zone 2
Data Access
Zone Host
Figure 4-9 Firewall physical separation of Inter-zone communications
Proxy Zone
Data Access 2 IP
Intranet Zone
In this figure, the number of firewalls with filtering routers was arbitrarily selected.
And remember from our firewall descriptions earlier, the “firewall router” may
consist of more than one physical box. The important point is that all connection
paths between any two adjacent zones must go through a firewall so we can