Looking Glass

Looking Glass. In computing, the term refers to a network diagnostic tool that provides a view into the routing and connectivity data of an autonomous system from an external perspective. Primarily used by network engineers and administrators, these tools query Border Gateway Protocol tables to help diagnose issues like route leaks, hijacks, and peering problems. The name is derived from the concept of seeing a network's state as if looking into a mirror from the outside.

Overview

A Looking Glass server is typically a web-based interface or command-line tool hosted by an Internet service provider, web hosting company, or large enterprise. It allows external users to run a limited set of diagnostic commands, such as traceroute, ping, and BGP route queries, against the host's network infrastructure. This provides invaluable data for troubleshooting without requiring direct access to the network's core routers. Major network operators like Cogent Communications, Hurricane Electric, and Level 3 Communications have historically provided public Looking Glass services. The tool is essential for verifying the propagation of IP address prefixes and assessing the impact of events like undersea cable cuts or configuration errors at major Internet exchange points.

History

The development of Looking Glass tools is inextricably linked to the growth and decentralization of the global Internet in the 1990s. As the BGP, defined in RFC 4271, became the standard for routing between autonomous systems, the need for external visibility into routing decisions grew. Early implementations were often simple Perl or Shell scripts providing telnet access to a router. The University of Oregon's Route Views Project, established in the late 1990s, provided a broader, more passive form of routing data collection that complemented active Looking Glass queries. Over time, as network security concerns increased, most public Looking Glass servers moved away from raw terminal access to more restricted and secure web interfaces, with features evolving to include queries for IPv6 routing and Multiprotocol Label Switching paths.

Technology and operation

Technically, a Looking Glass server acts as a controlled gateway to a router's command-line interface, often on a Cisco Systems or Juniper Networks device running IOS or Junos OS. When a user submits a query for a specific IP prefix, the server executes commands like `show ip bgp` and returns the best path information, showing the sequence of autonomous systems, known as the AS path. This data is crucial for identifying anomalies. The server software itself may be custom-built or use established platforms like the open-source Looking Glass project software. Advanced implementations may integrate with data from the RIPE NCC and Team Cymru's IP to ASN mapping services to provide richer context.

Cultural impact

Within the networking community, access to a robust Looking Glass is considered a mark of a transparent and professionally operated network. It fosters a culture of collaborative troubleshooting among engineers at different organizations, a principle embedded in the early ethos of the Internet Engineering Task Force. The tool has also entered the lexicon of Internet governance and security; discussions at forums like NANOG often reference Looking Glass data when analyzing global incidents. Furthermore, the conceptual "looking glass" has influenced cybersecurity tools, with projects like RiskIQ and Shodan offering commercial, expansive views of network surfaces that extend the original diagnostic idea.

Notable examples

Prominent examples of public Looking Glass servers include those operated by Telia Company (AS1299), which provides extensive views of its pan-European and transatlantic backbone, and Google's PeeringDB presence, which offers insights into its massive global infrastructure. The Merit Network's Route Servers provide another critical resource. Specialized variants exist, such as DNS Looking Glasses that test name server responses and IXP Looking Glasses that show local peering matrices at exchanges like DE-CIX in Frankfurt and LINX in London. These tools collectively form a foundational, if often invisible, layer of the operational Internet.

Category:Network management Category:Internet protocols Category:Network software