Cisco ASA Site-to-Site IPsec VPN Configuration
Configure site-to-site IPsec on the Cisco ASA the way 90 percent of production tunnels run today: IKEv2 with crypto maps, plus a section on route-based VTI for engineers who want the route-aware model.
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Latest posts — page 40
Cisco ASA Security Levels Explained: Inside, Outside, DMZ
Every ASA interface gets a security level from 0 to 100, and default forwarding between interfaces is decided entirely by that number. This article covers the convention, the same-security cases, and the day-one mistakes.
Cisco ASA ACL Configuration: Inbound Rules and Object Groups
ASA ACLs apply inbound, match the real untranslated destination IP, and lean on object groups for readability. This article walks the full model, the syntax, and the mistakes engineers coming from IOS hit on day one.
Cisco ASA Packet Flow: From Interface ACL to NAT to Route Lookup
Every packet crossing an ASA hits a deterministic series of checks: interface ACL, NAT, route lookup, and more. Walk all nine steps on software 9.x with a worked lab example, pinned to the config block you inspect when each step fails.
Cisco ASA NAT Explained: Auto NAT vs Manual NAT
ASA NAT changed completely in software 8.3, and old documentation still teaches the wrong model. This guide covers the modern one: Auto NAT vs Manual NAT, how they differ, and the order the ASA evaluates them.
Cisco ASA packet-tracer Command: Complete Troubleshooting Guide
packet-tracer simulates one packet through every ASA decision point, NAT, ACL, and route lookup included, and tells you exactly where it would be dropped. Covers the syntax, the common scenarios, and how to read each phase of the output.
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OSPF Field Reference (9-Page Printable Cheat-Sheet)
Nine printable pages of OSPF: the neighbor state machine, the six LSA types compared, area types and what each one filters, DR/BDR election rules, and the exact words to type when adjacency is stuck in EXSTART.
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BGP Field Reference (9-Page Printable Cheat-Sheet)
Nine printable pages of BGP: the neighbor state machine, the 13-step path selection algorithm, the major path attributes side by side, AS-path regex patterns, and the commands to type when an adjacency sticks in OpenSent.
GRE on Linux: ip tunnel add Commands and Examples
Configure GRE tunnels on Linux with ip tunnel add. Cisco-to-Linux interop, MTU, MSS clamping, IPsec, gretap (L2), and persistence with systemd-network
GRE Tunnel Troubleshooting: Recursive Routing and Five More Failures
The field guide for GRE failures on Cisco IOS XE, rebuilt around a real CML capture of a recursive-routing flap. The %ADJ-5-PARENT looped chain that lands just before %TUN-5-RECURDOWN, the administrative distance comparison that causes it, and three fixes: a static /32, filtering the transport...
mGRE and DMVPN Introduction
Multipoint GRE, NHRP, and IPsec combined to form DMVPN. The three phases, hub and spoke config for Phase 3, verification commands, and design tradeoff
Routing Protocols Over GRE: OSPF, EIGRP, BGP
Run OSPF, EIGRP, and BGP across GRE tunnels on Cisco IOS XE. Recursive routing fix, OSPF network types, EIGRP metric tuning, and BGP update-source.