Nine printable pages of BGP: the neighbor state machine, the 13-step path selection algorithm, the major path attributes side by side, AS-path regex patterns, and the commands to type when an adjacency sticks in OpenSent.
Configure GRE tunnels on Linux with ip tunnel add. Cisco-to-Linux interop, MTU, MSS clamping, IPsec, gretap (L2), and persistence with systemd-network
The field guide for GRE failures on Cisco IOS XE, rebuilt around a real CML capture of a recursive-routing flap. The %ADJ-5-PARENT looped chain that lands just before %TUN-5-RECURDOWN, the administrative distance comparison that causes it, and three fixes: a static /32, filtering the transport...
Multipoint GRE, NHRP, and IPsec combined to form DMVPN. The three phases, hub and spoke config for Phase 3, verification commands, and design tradeoff
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 compared: encryption, multicast, routing protocols, overhead, and a decision framework for site-to-site tunnel design.
GRE tunnel MTU and fragmentation explained: ip mtu 1400, ip tcp adjust-mss 1360, df-bit ping diagnostics, IPv6 considerations, and PMTUD black holes.
Cisco GRE keepalives explained: mechanism, configuration, IPsec rekey interactions, vendor interop, and the 30-second failover default that just works
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.
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: enabling IPv6, static and SLAAC addresses, RA options, OSPFv3, BGP for IPv6, EIGRP for IPv6, VRRPv3, dual-stack, and first-hop security.
The six IPv6 address types: global unicast, link-local, ULA, multicast, anycast, and special. Prefixes, scope, when to use which, and design implications.