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.
Local preference tells every router in your AS which exit to prefer for specific destinations. It rides iBGP throughout the AS and resolves in step 2 of best path. The cleanest tool for inbound exit engineering.
Most community write-ups stop at the set community line. This one follows the tag all the way through: R1 tags a prefix with 65001:200 and no-export, R2 prints the community and flags it as not advertised to EBGP peer, and R3 answers with % Network not in table. Captured on IOS XE 17.18.2 in CML.
Route maps are the primary BGP traffic engineering tool on Cisco IOS XE. Match on AS-path, community, or MED, then set attributes to steer paths. A practical guide to matching, setting, and manipulating BGP routes.
RPKI lets prefix owners sign ROAs that say which AS is authorized to originate their prefixes. Route Origin Validation rejects invalid routes. A practical guide to RPKI and ROV on Cisco IOS XE for internet-facing networks.
BGP was designed when every AS was trusted. Accidental route leaks and deliberate prefix hijacks have caused repeated major outages. How to detect them, prevent them, and protect your AS from the blast radius when others make mistakes.
Default BGP convergence can take 3 minutes to notice a dead peer. That is fine on the public internet and unacceptable in enterprise or data center BGP. Every knob for reducing BGP failover time on Cisco IOS XE, including BFD.
You set local-pref, route maps, and communities, and traffic still goes the wrong way. BGP is deterministic; a surprise path means either policy is not applied where you think, or a higher priority step decided first.
The BGP session is Established but routes are missing. A missing prefix can be stopped at any of several pipeline stages, from injection to best path to output filtering. A methodical troubleshooting guide to BGP route advertisement.
A BGP session that will not reach Established is the most common BGP issue. The FSM state tells you exactly where the problem is; the root cause inside each state can be one of many things. A systematic IOS XE methodology.
Service provider BGP operates at a scale that dwarfs enterprise: full tables, hundreds of peers, thousands of routers. An SP BGP design guide covering peering relationships, policy, iBGP scaling, and transit economics.
Enterprise BGP design comes down to how many ISPs, how many borders, full table or defaults, and active-active or active-standby. From single-homed to multi-homed with traffic engineering, and when you do not need BGP at all.