> 1) different switch on the each side of the firewall
> 2) different switch on the each side of the firewall, 
>    accidentally cabled together
> 3) single switch connects both sides of the firewall, 
>    accidentally no VLAN separation
> 4) single managed switch connects both sides of the firewall, 
>    separated by VLAN
> 
> 1) Only penetration attack is to break the firewall
> 2) If a bridging firewall is in use then the switches 
>    short-circuit the firewall and the network is wide open.
>    If a routing firewall is in use, a successful attack
>    requires the internet router's inside interface to be 
>    reconfigured to use an address on the firewall's internal 
>    network.  If the router's inside address is not
>    reconfigured, return packets from the inside would still
>    traverse the firewall, which should discard them 
>    (wrong state).
> 3) exactly the same as #2.

If you break a bridging firewall, it just blocks all, it stops
the bridging.

> 4) With a bridging firewall, the attacker can penetrate by 
>    breaking the switch (assuming remotely-exploitable vulnerabilites).
>    With a routing firewall, attacker must break both the router and
>    the switch.  Same router configuration applies as for #2.

A bridging firewall will still chek, VLAN-tags, host ranges assigned
per VLAN, zones assigned per interface, VLAN's per zone etc.

Breaking the switch will not break the firewall.

> So... are routing firewalls more secure than bridging ones in this 
> example?  I think examples #2 and #3 are more likely than someone 
> accidentally connecting and configuring a new router which 
> short-circuits the firewall.

I agree with situation #2 only.


Sorry for not going into the VLAN discussion...
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