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    "title": "Perlman: a spanning tree for a bridged network",
    "summary": "Perlman gives a distributed protocol that selects a root and forwarding subset of a bridged extended LAN, preserving connectivity while removing forwarding loops after convergence, with explicit aging and reconfiguration delays.\n\nConnecting local networks with redundant bridges offers backup paths, but it can also let packets circulate indefinitely around a loop. Radia Perlman gives the bridges a way to select a usable tree without requiring changes to ordinary connected stations. Each bridge advertises its view of the root and its distance; a designated bridge is selected for each local network, and other forwarding links are disabled. The protocol also ages old information and delays forwarding changes so that bridges can recover when links or the root fail. Its control state depends on a bridge’s attached links rather than requiring a map of the whole network. The paper separates stable-tree reasoning from timer choices needed during reconfiguration. It does not supply a defense against arbitrary malicious announcements, and its guarantees depend on connectivity, unique identifiers and suitable timing bounds. Equal-distance upstream links can be chosen arbitrarily in the stated algorithm, so a unique root does not mean every final port choice is unique.",
    "boundary": "The algorithm selects a loop-free spanning tree among bridges using the stated identifiers, messages and timing assumptions. Convergence after topology changes differs from instantaneous forwarding safety. It does not guarantee shortest paths, Byzantine/Sybil robustness or unlimited dynamic-network behavior. Later standardized variants and implementations are separate.",
    "area": "Computer science",
    "topic": "Network protocols",
    "year": 1985,
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        "title": "Perlman1985: An algorithm for distributed computation of a spanning tree in an extended LAN",
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      "scope": {
        "description": "The algorithm selects a loop-free spanning tree among bridges using the stated identifiers, messages and timing assumptions. Convergence after topology changes differs from instantaneous forwarding safety. It does not guarantee shortest paths, Byzantine/Sybil robustness or unlimited dynamic-network behavior. Later standardized variants and implementations are separate.",
        "domain": "Computer science"
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      "sources": [
        {
          "citation": "Perlman1985: An algorithm for distributed computation of a spanning tree in an extended LAN",
          "url": "https://people.cs.umass.edu/~phillipa/CSE390/p44-perlman.pdf"
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      "statement": "# Perlman: a spanning tree for a bridged network\n\nPerlman gives a distributed protocol that selects a root and forwarding subset of a bridged extended LAN, preserving connectivity while removing forwarding loops after convergence, with explicit aging and reconfiguration delays.\n\nConnecting local networks with redundant bridges offers backup paths, but it can also let packets circulate indefinitely around a loop. Radia Perlman gives the bridges a way to select a usable tree without requiring changes to ordinary connected stations. Each bridge advertises its view of the root and its distance; a designated bridge is selected for each local network, and other forwarding links are disabled. The protocol also ages old information and delays forwarding changes so that bridges can recover when links or the root fail. Its control state depends on a bridge’s attached links rather than requiring a map of the whole network. The paper separates stable-tree reasoning from timer choices needed during reconfiguration. It does not supply a defense against arbitrary malicious announcements, and its guarantees depend on connectivity, unique identifiers and suitable timing bounds. Equal-distance upstream links can be chosen arbitrarily in the stated algorithm, so a unique root does not mean every final port choice is unique.\n\n## Scientific scope\n\nThe algorithm selects a loop-free spanning tree among bridges using the stated identifiers, messages and timing assumptions. Convergence after topology changes differs from instantaneous forwarding safety. It does not guarantee shortest paths, Byzantine/Sybil robustness or unlimited dynamic-network behavior. Later standardized variants and implementations are separate.\n\n## People and systems\n\nRadia Perlman\n\n\n\n## Original sources\n\n- [Perlman1985: An algorithm for distributed computation of a spanning tree in an extended LAN](https://people.cs.umass.edu/~phillipa/CSE390/p44-perlman.pdf)\n- [RFC6325(2011): Routing Bridges base protocol, abstract and authors only](https://www.rfc-editor.org/info/rfc6325/)\n",
      "summary": "Perlman gives a distributed protocol that selects a root and forwarding subset of a bridged extended LAN, preserving connectivity while removing forwarding loops after convergence, with explicit aging and reconfiguration delays.\n\nConnecting local networks with redundant bridges offers backup paths, but it can also let packets circulate indefinitely around a loop. Radia Perlman gives the bridges a way to select a usable tree without requiring changes to ordinary connected stations. Each bridge advertises its view of the root and its distance; a designated bridge is selected for each local network, and other forwarding links are disabled. The protocol also ages old information and delays forwarding changes so that bridges can recover when links or the root fail. Its control state depends on a bridge’s attached links rather than requiring a map of the whole network. The paper separates stable-tree reasoning from timer choices needed during reconfiguration. It does not supply a defense against arbitrary malicious announcements, and its guarantees depend on connectivity, unique identifiers and suitable timing bounds. Equal-distance upstream links can be chosen arbitrarily in the stated algorithm, so a unique root does not mean every final port choice is unique.",
      "title": "Perlman: a spanning tree for a bridged network"
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    "id": "perlman-distributed-bridge-spanning-tree-1985",
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    "what_changed": "Perlman gives a distributed protocol that selects a root and forwarding subset of a bridged extended LAN, preserving connectivity while removing forwarding loops after convergence, with explicit aging and reconfiguration delays.",
    "scope": "Perlman gives a distributed protocol that selects a root and forwarding subset of a bridged extended LAN, preserving connectivity while removing forwarding loops after convergence, with explicit aging and reconfiguration delays. The algorithm selects a loop-free spanning tree among bridges using the stated identifiers, messages and timing assumptions. Convergence after topology changes differs from instantaneous forwarding safety. It does not guarantee shortest paths, Byzantine/Sybil robustness or unlimited dynamic-network behavior. Later standardized variants and implementations are separate.",
    "evidence_summary": "Source-linked, scoped account of the original work. The published scope states the scientific assumptions and remaining verification limits. WRS has not independently certified the full proof, experimental result or system benchmark.",
    "references": [
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        "title": "Perlman 1985: An algorithm for distributed computation of a spanning tree in an extended LAN",
        "url": "https://people.cs.umass.edu/~phillipa/CSE390/p44-perlman.pdf",
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