Cisco Adaptive Security Appliance, the stateful firewall platform that has anchored enterprise perimeters for two decades and is now being succeeded by Secure Firewall (FTD). Articles tagged ASA cover security levels, NAT 8.3+ and twice NAT, ACLs, AnyConnect SSL and IKEv2 VPN, site-to-site IPsec, failover, packet-tracer, hardening, and ASAv 9.x lab walkthroughs.
Connections that die crossing the ASA with no ACL deny are usually TCP normalization. You see the real tcp-map and accelerated-security-path drop counters from an ASAv 9.24 that turn this silent killer into something visible.
Build a custom Layer 7 HTTP inspection policy on the ASA that blocks a specific URL by regex, then prove it with a real before-and-after test: one URL loads instantly, the other hangs until timeout. Captured on an ASAv 9.24 in CML.
L3 and L4 filtering is half a firewall. This post shows the ASA's application inspection engines in action on a real ASAv 9.24 in CML, including the default inspection policy and live per-interface counters.
MPF is the engine under nearly every advanced ASA feature. Build class-maps, policy-maps, and service-policies from scratch on a real ASAv 9.24 in CML, with live counters climbing as a Linux client hits a published web server.
Failover, clustering, contexts, redundant interfaces: the ASA HA menu is long. We tested every option live on asav 9.24, so each supported or rejected cell in this comparison is a tested fact, not a datasheet claim.
Cisco ASA clustering pools up to sixteen units into one logical firewall that shares load and state. This article explains spanned vs individual interface mode, plus a real capture of ASAv 9.24 rejecting the cluster commands and what that tells you.
Multiple ASA contexts draw from the same connection, translation, and inspection pools. Resource classes cap and guarantee slices of firewall capacity so one busy context cannot starve the rest.
When ASA security contexts share a physical interface, the classifier decides which context owns each incoming packet before any policy applies. Learn the classification rules that keep multi-tenant traffic out of the wrong tenant.
Active/Active failover needs multiple context mode and invites asymmetric routing. Watch a real ASAv 9.24 refuse the mode, then see the capture that proves what you should be running instead for most deployments.
How EtherChannel bundles ASA links into one pipe with LACP, and how it interacts with failover. Includes a real-lab reality check: the ASAv 9.24 parser rejects every Port-channel command, and we show you exactly where.
ASA redundant interfaces bundle two physical ports into one logical interface for fast link-level HA without full unit failover. We tried it on a real ASAv 9.24, the parser refused, and that rejection is the most useful part of this post.
Since ASA 8.3, interface ACLs reference the real, post-translation IP, never the mapped one. A before-and-after on one flow, allowed with a real-IP rule and dropped with a mapped-IP rule, settles the most misunderstood ASA behavior.