How OSPF SPF Algorithm and LSDB Work
OSPF builds the LSDB, then runs Dijkstra (SPF) to calculate best paths. Here is what triggers partial vs full SPF and how to tune the throttle timers.
Archive
Latest posts — page 54
OSPF LSA Types Explained (Type 1 to 7) with Real LSDB Output
show ip ospf database prints five section headers and none of them says "Type 1". Here is every LSA type identified on real output from a three-router, two-area CML lab with an ASBR, on IOS XE 17.18.2, plus the route code each type ends up as.
OSPF Subnet Mask Mismatch: How to Troubleshoot and Fix
On broadcast networks, mismatched subnet masks leave OSPF stuck in Init or 2-Way. Here is the fast diagnosis with show ip ospf neighbor and the one-line fix.
OSPF Design Best Practices for Enterprise Networks
Real OSPF design rules: keep Area 0 stable and small, cap routers per area, use stub where you can, and make summarization a feature of your area boundaries.
Understanding RADIUS in 802.1X Authentication
RADIUS is the glue between a Catalyst switch and Cisco ISE in 802.1X. Here is how the Access-Request carries EAP, why UDP 1812/1813 matters, and where failures surface.
EAPOL Explained: How 802.1X Traffic Moves Over the Wire
EAPOL carries EAP between the supplicant and switch at Layer 2. It never leaves the segment, which is why captures and debug have to happen on or at the port.
How EAP Works in 802.1X: EAP Methods Compared
EAP is a framework, not a protocol. Compare EAP-TLS, PEAP-MSCHAPv2, EAP-FAST, and EAP-TTLS by credential type, tunnel, and where each belongs in enterprise 802.1X.
802.1X Components Explained: Supplicant, Authenticator, and Authentication Server
802.1X splits work across three roles: supplicant, authenticator, and authentication server. Understanding the boundaries explains both the config and the failure points.
What Is 802.1X? Port-Based Network Access Control Explained
802.1X is port-based network access control. It forces a device to authenticate before the switch forwards traffic, closing the wall-jack gap in modern enterprise networks.
MAC Authentication Bypass (MAB) Configuration on Cisco IOS XE and ISE
MAB authenticates printers, cameras, and legacy gear that cannot run a supplicant by using their MAC as the RADIUS username. Here is the Cisco IOS XE and ISE config.
Configuring EAP-TLS with Certificates on Cisco ISE and IOS XE
EAP-TLS replaces 802.1X passwords with mutual certificate auth. Here is the PKI prep, ISE policy, and IOS XE config you need for a production certificate-based rollout.
Configuring PEAP Authentication with Cisco ISE and IOS XE
PEAP-MSCHAPv2 protects the credential exchange inside a TLS tunnel against an ISE server certificate. Here is the full Cisco ISE and IOS XE config for AD users.