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
Tunnels
Latest 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
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.
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 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.
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.