Routing

Exact /api finishes selection. The longest ordinary prefix can be replaced by a matching regex; a selected ^~ prefix bypasses regex. With no regex match, the remembered prefix wins.

An nginx prefix is a candidate until matching finishes

An nginx location selects configuration for a request within the chosen server. For the flat prefix and regex locations tested here, an exact match finishes the search; otherwise nginx remembers the longest matching prefix and can then choose the first matching regex. If no applicable regex wins, the remembered prefix supplies the configuration. This is a selection process, not simply the first block encountered in the file. ...

Several replicas advertise one prefix; the observing network chooses a usable path according to routing policy. Routing nearest is not a geographic-distance guarantee.

Anycast lets routing select a replica

Anycast gives an address several homes. Multiple sites announce the same prefix, and each network selects a usable path according to routing policy. This article focuses on Internet BGP; local anycast can use an interior routing protocol. A client usually lands at a topologically close replica without first contacting a global load balancer. When one site withdraws its announcement, the control plane can converge on another home. ...

A /16 summary encloses two /24 components and unfilled space. One component can disappear while the other retains its route; unmatched summary traffic at the aggregator needs discard handling.

BGP aggregation shrinks the routing table

Aggregation can replace several more-specific advertisements with one covering prefix. It reduces downstream table entries only where the specifics are actually suppressed and no alternative peer supplies them. The components need not fill the whole summary: advertising a sparse block also attracts traffic for its holes. Aggregation therefore combines a scaling decision with a reachability and ownership decision. ...

Intended source scenario, not an observed run. Client, router and target are connected in the request direction. A crossed return line marks removal of the target return default. The client gateway stays unchanged but the HTTP attempt times out, showing why a route out still needs a route back.

A default route matches broadly; it does not rescue every failed path

An IPv4 default route is the prefix 0.0.0.0/0: it matches every IPv4 destination, with the least possible specificity. In a selected routing table, a longer matching prefix normally takes precedence. The default is not a procedure that retries whenever a more specific route fails. Routing policy selects relevant tables, and the chosen route describes a forwarding decision rather than promising that the entire round trip will succeed. ...

For the same prefix in the article two-field model, local preference 200 selects a three-AS path over a shorter two-AS path with preference 100.

BGP is the Internet routing table

BGP exchanges reachability between independently operated networks, but there is no single authoritative Internet forwarding table. Each router learns a policy-filtered view, chooses routes, and attempts to install usable next hops. Two routers can legitimately select different paths to the same prefix. Understanding BGP means separating announcements, selection policy, and packet forwarding rather than treating them as one universal answer. ...

Two aligned columns replace /replace/ with /v1/ while preserving item?x=1. This is literal proxy URI prefix replacement.

proxy_pass maps the URI as well as selecting an upstream

nginx proxy_pass chooses an upstream destination and also affects the request URI sent there. The important distinction is whether the directive includes a URI component, not simply whether its text ends with a slash. In an ordinary prefix location, a literal target URI replaces the matching normalized prefix. An authority-only target can pass the original request URI when the request has not been rewritten. ...