For Defense in depth I would use multi-tiered approach. Stateless ACL at Border for bound checks Stateful FW for Checking sessions Outbound ACLs on Innerchoke points Application Intelligence and DDOS mitigation by IPS between Border and Firewall Endpoint Security using Enterprise Anti-Virus agents/NAC Agents Regards Ubaidali Abdul Razack +65.65436404 (Office) +65.65436278 (Fax) Roland Dobbins <rdobbins@cisco.com> 04/08/2009 08:28 AM To NANOG list <nanog@nanog.org> cc Subject Re: ACLs vs. full firewalls On Apr 8, 2009, at 4:05 AM, Michael Helmeste wrote:
However, I wanted to get other opinions of what packet filtering solutions people use in the border and in the core, and why.
Stateless ACLs in hardware at the edge are important both for infrastructure self-protection (i.e., iACLs) and for policy enforcement of the type you indicate. As others on this thread have pointed out, do understand your platform characteristics and craft your ACLs accordingly. Stateful - i.e., context-aware bidirectional - filtering via a firewall makes sense in situations in which a) the nodes 'behind' the firewall aren't typically operating as servers and/or b) the bidirectional communications patterns which should be observed are well-known, and in which the participation of hosts is under the control/influence of the network operator. For example, in front of a corporate LAN, or between the tiers of a multi-tiered application, one can craft quite specific stateful inspection rules which can be used to explicitly allow and disallow certain types of traffic. For front-end, publicly-accessible conventional servers, stateful inspection may not add as much value, as basically every connection which comes into those servers is unsolicited (i.e., no existing stateful communications context against which to measure pass/fail decisions); this is where high-speed stateless ACLs, coupled with host OS/app/service hardening play a key role. It's very important to avoid the instantiation of unnecessary state in front of public-facing assets, as DDoS attacks are essentially attacks against capacity and against state. One should also look into implementing DDoS mitigation techniques such as S/RTBH, in conjunction with the chosen policy-enforcement regime. ----------------------------------------------------------------------- Roland Dobbins <rdobbins@cisco.com> // +852.9133.2844 mobile Our dreams are still big; it's just the future that got small. -- Jason Scott Please consider the environment before printing this e-mail. _______________________ CONFIDENTIALITY NOTICE: This e-mail message, including any attachments, is being sent by 3Com for the sole use of the intended recipient(s) and may contain confidential, proprietary and/or privileged information. Any unauthorized review, use, disclosure and/or distribution by any recipient is prohibited. If you are not the intended recipient, please delete and/or destroy all copies of this message regardless of form and any included attachments and notify 3Com immediately by contacting the sender via reply e-mail or forwarding to 3Com at postmaster@3com.com.