Cisco

Cisco networking tutorials covering IOS and IOS-XE configuration, platform features, and hands-on guides for routing, switching, and security across Cisco hardware and software.

134 posts

GRE Tunnel Troubleshooting Guide

Step-by-step GRE tunnel troubleshooting on Cisco IOS XE. Five-minute triage, recursive routing, MTU drops, keepalive flap, debug commands, and EPC cap

7 min read May 1, 2026

GRE public

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

7 min read May 1, 2026

GRE public

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.

8 min read May 1, 2026

GRE public

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.

6 min read May 1, 2026

GRE public

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.

6 min read May 1, 2026

GRE public

GRE Tunnel Keepalives Explained

Cisco GRE keepalives explained: mechanism, configuration, IPsec rekey interactions, vendor interop, and the 30-second failover default that just works

6 min read May 1, 2026

GRE public

GRE over IPsec: When and How to Combine Them

Configure GRE over IPsec on Cisco IOS XE with IKEv2 and IPsec profiles. Modern and legacy configs, MTU planning, OSPF over the tunnel, and gotchas.

7 min read May 1, 2026

GRE public

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.

9 min read May 1, 2026

IPv6 public

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.

5 min read Apr 26, 2026

IPv6 public

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.

4 min read Apr 26, 2026

IPv6 public

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.

5 min read Apr 26, 2026

IPv6 public

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.

4 min read Apr 26, 2026