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
Blog
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.
7 min read
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
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
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
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.
5 min read