IPsec over GRE vs GRE over IPsec
"IPsec over GRE" and "GRE over IPsec" sound like the same thing said two ways. They are not. They are two different designs with the encapsulation layers stacked in the opposite order, and the order changes
Fundamentals
Networking fundamentals and CCNA-level reference content. The TCP/IP and OSI models, ethernet basics, encapsulation, IPv4 addressing, layer 2 fundamentals, and the Cisco IOS commands every network engineer reaches for. The foundations beneath the pillar guides.
Latest posts
IPv6 Address Examples: Every Type, Worked Through
IPv6 addresses look intimidating until you have seen enough real ones to recognize the patterns. The first hextet usually tells you everything: what kind of address it is and what it is for. This post is a worked reference - one
HSRP Configuration on Cisco IOS XE
HSRP configuration is short - a working setup is two lines per router - but the short config hides the decisions that actually matter. Which router is active, whether it stays active after a reboot, and what happens when its uplink fails
MPLS Traffic Engineering Explained
MPLS Traffic Engineering exists to solve a problem the IGP creates. OSPF and IS-IS always forward along the shortest path, every flow, all the time. That is correct for reachability and terrible for capacity: the shortest path saturates while
TFTP vs FTP for Cisco IOS File Transfers and Config Backup
Sooner or later every engineer copies something onto or off a router: a config backup before a risky change, a new IOS image, a crash dump for TAC. The two classic transports are TFTP and FTP, they behave very differently,
DHCP and DNS on Cisco Networks: Roles, Relay, and ip helper-address
DHCP hands a host its network identity; DNS makes names usable instead of addresses. The CCNA asks you to keep their roles straight and to configure a router as a DHCP server and relay, and the relay part is where
Syslog on Cisco IOS XE: Severity Levels, Logging Host, and Real Messages
When something breaks at 3 a.m., the first question is "what changed, and when?" Syslog is the answer, but only if you set it up before the outage: severity levels chosen deliberately, messages shipped off-box to
SNMP Explained: v2c vs v3, OIDs, MIBs, and Real Polling
SNMP is how monitoring systems actually know your interface went down, your CPU spiked, or your optics are running hot. Every NMS you will ever deploy (LibreNMS, Zabbix, SolarWinds, Catalyst Center's assurance features) speaks it. This article explains
NTP on Cisco IOS XE: Stratum, ntp master, and Verification
Wrong time on a network device is not a cosmetic problem. Certificate validation fails, log timestamps become useless for incident correlation, and time-based authentication (like 802.1X with certificates, or API tokens) starts breaking in ways that look random.
NAT on Cisco IOS XE: Static, Dynamic, and PAT Configuration
NAT is the reason your private 10.x network can talk to the internet, and it is also one of the CCNA topics where the terminology trips up more people than the configuration. Cisco IOS XE gives you three flavors:
AI and Machine Learning in Network Operations
The CCNA v1.1 refresh added artificial intelligence and machine learning to the blueprint, and it is one of the few topics where the competition has not caught up yet. You are not expected to build models; you are expected
Ansible vs Puppet vs Chef (and Terraform) for Network Automation
Once you accept that configuring devices one at a time does not scale, the next question is which tool does the configuring for you. The CCNA v1.1 blueprint names three configuration-management tools (Ansible, Puppet, Chef) and, with the