{
    "@context": "https://schema.org",
    "@type": "DefinedTerm",
    "@id": "https://hostdir.net/glossary/looking-glass",
    "name": "Looking Glass",
    "description": "A looking glass is a public web-based tool that provides read-only access to a network's BGP routing table, ping, and traceroute diagnostics from that network's perspective.",
    "url": "https://hostdir.net/glossary/looking-glass",
    "inDefinedTermSet": "https://hostdir.net/glossary",
    "termCode": "looking-glass",
    "mainEntityOfPage": "https://hostdir.net/glossary/looking-glass",
    "license": "https://creativecommons.org/licenses/by/4.0/",
    "_hostdir": {
        "kind": "glossary-term",
        "slug": "looking-glass",
        "canonical": "https://hostdir.net/glossary/looking-glass",
        "term": "Looking Glass",
        "category": "Networking & Routing",
        "category_slug": "networking-routing",
        "summary": "A looking glass is a public web-based tool that provides read-only access to a network's BGP routing table, ping, and traceroute diagnostics from that network's perspective.",
        "definition": "A looking glass is a web application that allows external users to query routing and connectivity information from a remote network's router. It typically provides read-only access to the router's BGP table, as well as the ability to run ping and traceroute commands. The output reflects what the network itself sees, offering a valuable external viewpoint for troubleshooting and verification.\n\nHow it works: A looking glass server accepts requests via a web interface, then connects to a router (often via SSH or telnet) and executes the requested command. The output is captured and displayed back to the user. The commands are usually restricted to show commands and diagnostic tools, preventing any configuration changes. Many large ISPs, Internet Exchange Points (IXPs), and backbone operators maintain public looking glasses for community use.\n\nIn the wider stack, a looking glass sits as a monitoring and diagnostic tool for the global routing system. It complements route collectors and route servers by giving a point-in-time snapshot of a specific network's routing state. Network engineers use it to verify BGP prefix announcements, check path selection, or test latency and reachability from a remote location. It is a lightweight but essential resource for operational debugging and research.",
        "examples": "A network engineer at a small ISP wants to confirm that their prefix is being advertised by a Tier 1 provider. They visit that provider's looking glass website, enter their prefix in the BGP route lookup field, and see that the route is present with the expected AS path. This confirms the announcement is propagating correctly.",
        "key_facts": [
            "Provides read-only access to BGP routes, ping, and traceroute from a specific network's perspective.",
            "Typically implemented as a CGI or web application that executes commands on a router.",
            "Commonly offered by ISPs, IXPs, and large network operators for public use.",
            "Allows external users to verify BGP announcements and troubleshoot routing issues.",
            "Commands are restricted to show and diagnostic functions to prevent configuration changes."
        ],
        "related_terms": [
            "BGP",
            "traceroute",
            "ping",
            "route server",
            "Internet Exchange Point (IXP)",
            "network operations center (NOC)"
        ],
        "references": [
            {
                "title": "Looking Glass (Wikipedia)",
                "url": "https://en.wikipedia.org/wiki/Looking_Glass_(Internet)"
            },
            {
                "title": "RFC 4271: A Border Gateway Protocol 4 (BGP-4)",
                "url": "https://datatracker.ietf.org/doc/html/rfc4271"
            },
            {
                "title": "RFC 792: Internet Control Message Protocol",
                "url": "https://datatracker.ietf.org/doc/html/rfc792"
            }
        ],
        "word_count": 206,
        "license": "CC BY 4.0",
        "license_url": "https://creativecommons.org/licenses/by/4.0/",
        "attribution": "HostDir Glossary — https://hostdir.net/glossary/looking-glass"
    }
}