Firewalls in service provider environments
Justin M. Streiner
streiner at cluebyfour.org
Tue Feb 7 15:46:04 CST 2012
On Tue, 7 Feb 2012, Matthew Reath wrote:
> Looking for some recommendations on firewall placement in service provider
> environments. I'm of the school of thought that in my SP network I do as
> little firewalling/packet filtering as possible. As in none, leave that to
> my end users or offer a "managed" firewall solution where if a customer
> signs up for the extra service I put him in a VRF or VLAN that is "behind"
> a firewall and manage that solution for them. Otherwise I don't prefer to
> have a firewall inline in my service provider network for all customer
> traffic to go through. I can accomplish filtering of known bad ports on my
> edge routers either facing my customers or upstream providers.
I tend to agree with this, and I think you'll find that most providers
agree with that as well.
There are several reasons for this:
1. Firewalls present another point of failure, and SPs are generally loath
to force customer traffic* through another choke point.
2. Many firewall appliances are stateful. Multihomed customers and
stateful firewalls can be a major headache. Asymmetric routing through
stateful firewalls is pretty much a non-starter.
3. You (the customer) know your applications and internal network better
than the SP does. It makes sense for you to manage your firewalls/NAT/
internal LAN. If you can't or don't want to do this, hire a consultant to
do the work for you.
4. Most SPs would not want the liability of managing firewall service.
5. Dropping packets at the SP edge could be done, but I think most SPs
would only want to do so in extraordinary circumstances.
* - As you mentioned, unless the SP offers, and those customers
specifically pay for a firewalled service.
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