VPN

Every error message in this article came off a real router. Not a textbook, not a vendor doc, not a

Every IPsec engineer eventually hits the same wall. The tunnel worked perfectly in the lab, you shipped the branch router,

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.

Almost everything written about IPsec starts with a config snippet. That is backwards. If you do not know what an

A site-to-site VPN built with crypto maps is still the config the CCIE Security lab expects you to