Dynamic routing on firewalls.

Thu Feb 5 14:51:28 UTC 2015

It all depends how much of the firewall functionality is implemented in CPU.

The biggest problem is that firewalls that implement functionality in
software usually saturate CPU when stressed (e.g. DOS) and routing
protocols start dropping.

I'm a strong believer in having a router that can do basic filtering
in hardware (specifically uRPF) as the first line of defense in a DOS
attack and then using a firewall behind that to reach your security
policy goals.  We have a pretty large network so we've expanded the
concept of RTBH filtering internally and use a small ISR (currently
1841) to inject routes into our network to disable hosts using uRPF at
the first router they hit.  The entire thing is scripted and works
very well at containing problematic hosts centrally.

The other thing to watch out for IMHO is the NGFW hype.  I haven't
seen a NGFW that can actually do everything it claims to at the same
time and meet advertised performance levels.  You're much better off
splitting up the workload and having a series of components
architected to work with each other.

On Thu, Feb 5, 2015 at 9:42 AM, Eugeniu Patrascu <eugen at imacandi.net> wrote:
> On Thu, Feb 5, 2015 at 4:10 PM, David Jansen <david at nines.nl> wrote:
>
>> Hi,
>>
>> We have used dynamic routing on firewall in the old days. We did
>> experience several severe outages due to this setup (OSPF en Cisco). As you
>> will understand i'm not eager to go back to this solution but I am curious
>> about your point of views.
>>
>> Is it advisory to so these days?
>>
>>
> Any specific firewall in mind? As this depends from vendor to vendor.
>
> I've had some issues with OSPF and CheckPoint firewalls when the firewalls
> would be overloaded and started dropping packets at the interface level
> causing adjacencies to go down, but I solved this by using BGP instead and
> the routing issues went away.
>
> On Juniper things tend work OK.
>
> Other than this, make sure you don't run into asymmetric routing as
> connections might get dropped because the firewall does not know about them
> or packets arrive out of order and the firewall cannot reassemble all of
> them.

-- 
Ray Patrick Soucy
Network Engineer
University of Maine System

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