Border Gateway Protocol, the path-vector protocol that holds the internet together and increasingly runs inside enterprise data centers. Articles tagged BGP cover fundamentals, neighbor states, path attributes, best-path selection, traffic engineering, and Cisco IOS XE configuration.
A WAN-to-self ZBF policy meant to restrict management kept SSH working, but OSPF hit its dead timer about 8 seconds later and loopback eBGP followed on hold-time expiry. OSPF pass and BGP inspect on both self zone-pairs fixed it.
EVPN route types stop being abstract the moment you read them off a real fabric. Here are Types 2, 3 and 5 from a working Nexus lab.
The prefix is in the BGP table and show ip route says % Network not in table. The leading status characters are the whole diagnosis. Captured live on IOS XE 17.18.2 in CML, where a missing next-hop-self leaves an iBGP path valid, inaccessible and never installed.
Active is a failure state and Idle is where the FSM gives up. Organized by the state you are looking at right now, with a lab finding that matters: on IOS XE 17.18.2 both "no route to peer" and "TCP 179 blocked" showed up as Idle.
OMP carries everything in Catalyst SD-WAN: routes, TLOCs, service routes, keys, and policy. This deep dive walks each advertisement type and the path selection logic, with WAN Edge CLI drawn from Cisco's current 20.x documentation.
When two customer sites share an AS number, BGP loop prevention breaks their MPLS L3VPN on purpose. Reproduce the failure in a CML lab and fix it three ways: as-override, allowas-in, and SoO, with real output for each.
6VPE carries IPv6 L3VPN across an IPv4 MPLS core using the same VRFs, RTs, and MP-BGP sessions you already run. This article builds it in CML and shows the two-label stack that makes it work.
Two-point redistribution is where networks go to die. This article builds the classic CCIE failure for real in a CML lab, shows a route being re-injected into the protocol it came from, and then fixes it with the exact output at each step.
Five broken BGP scenarios built and broken for real in a CML lab, each worked ticket style with the actual diagnostic output and the actual fix. The method: every BGP problem is one of four things, checked in order.
6PE carries IPv6 prefixes across an untouched IPv4 MPLS core using MP-BGP and labels. This post builds a working deployment on Cisco IOS XE and shows the labels, the IPv4-mapped next hops, and an end-to-end IPv6 traceroute.
BGP multipath is one config line, but the rules for when a second path is accepted are not. Cover eBGP, iBGP, and eiBGP multipath on Cisco IOS XE with lab output, including the next-hop rewrite that can hide a real misconfiguration.
A well-designed BGP community scheme turns per-neighbor route-maps into a scalable signaling system. This guide builds one end to end on IOS XE, proves it with lab output, and includes a working RTBH trigger.