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
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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.
GRE vs IPsec vs GRE-over-IPsec: Which Tunnel Type?
GRE vs IPsec vs GRE-over-IPsec compared: encryption, multicast, routing protocols, overhead, and a decision framework for site-to-site tunnel design.
GRE MTU and Fragmentation: Fixing Tunnel Packet Loss
GRE tunnel MTU and fragmentation explained: ip mtu 1400, ip tcp adjust-mss 1360, df-bit ping diagnostics, IPv6 considerations, and PMTUD black holes.
GRE Tunnel Keepalives Explained
Cisco GRE keepalives explained: mechanism, configuration, IPsec rekey interactions, vendor interop, and the 30-second failover default that just works
GRE Tunnel Configuration: Step-by-Step Cisco IOS XE Lab
Build a GRE tunnel between two Cisco IOS XE routers step by step: tunnel interface, MTU, keepalives, OSPF over the tunnel, and recursive-routing fix.
IPv6 Header Format Explained
The IPv6 header byte by byte: 40 bytes fixed, 8 fields, extension headers, Next Header chaining, comparison to IPv4, and what it looks like in Wireshark.
IPv6 Configuration on Cisco IOS XE
IPv6 configuration on Cisco IOS XE: enabling IPv6, static and SLAAC addresses, RA options, OSPFv3, BGP for IPv6, EIGRP for IPv6, VRRPv3, dual-stack, and first-hop security.
IPv6 Address Types: Link-Local, Global, Unique Local
The six IPv6 address types: global unicast, link-local, ULA, multicast, anycast, and special. Prefixes, scope, when to use which, and design implications.
IPv4 vs IPv6: The Real Differences
IPv4 vs IPv6 in 2026. Header differences, ARP vs Neighbor Discovery, SLAAC vs DHCP, NAT vs end-to-end, and dual-stack as the migration reality.
IPv6 Address Format Explained Byte by Byte
IPv6 addresses are 128 bits as eight groups of four hex digits. The two compression rules, prefix notation, EUI-64 interface IDs, special addresses, and worked examples.
HSRP vs VRRP vs GLBP: All Three Running Side by Side
Most FHRP comparisons are a table and nothing else. This one runs HSRP, VRRP and GLBP at the same time on the same two routers, so you can read Active/Standby against MASTER/BACKUP against AVG/AVF, decode each protocol's virtual MAC, and watch GLBP keep both routers forwarding for one virtual...