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Documentation Prelude Topology Engine 1.0.0

Prefixes

The fields Prelude TE surfaces on each prefix, including SR-MPLS Prefix SIDs with decoded flags and SRv6 locator metadata.

A prefix in the topology is an IP prefix (IPv4 or IPv6) advertised by a node as reachable through it. This page documents every field the engine surfaces on a prefix.

Example payloads

These two examples show only the common fields. When the prefix also carries an SR-MPLS Prefix SID or SRv6 locator metadata, the export grows an sr-mpls or srv6 block as documented in the sections below.

IPv4 prefix

{
  "key": "ASN:64001/BGPLS:100/IGP:0001.0000.0006/10.2.6.0/24",
  "safe-id": "ASN_64001_BGPLS_100_IGP_0001_0000_0006_10_2_6_0_24",
  "instance-id": 100,
  "node-key": "ASN:64001/BGPLS:100/IGP:0001.0000.0006",
  "prefix": "10.2.6.0/24",
  "prefix-length": 24,
  "ip-version": 4,
  "metric": 0,
  "source-peers": ["172.31.0.200", "172.31.0.100"],
  "last-update": "2026-05-26T11:22:45.594293+02:00"
}

IPv6 prefix

{
  "key": "ASN:64001/BGPLS:100/IGP:0001.0000.0006/fc00:1:6::/48",
  "safe-id": "ASN_64001_BGPLS_100_IGP_0001_0000_0006_fc00_1_6___48",
  "instance-id": 100,
  "node-key": "ASN:64001/BGPLS:100/IGP:0001.0000.0006",
  "prefix": "fc00:1:6::/48",
  "prefix-length": 48,
  "ip-version": 6,
  "metric": 0,
  "source-peers": ["172.31.0.200", "172.31.0.100"],
  "last-update": "2026-05-26T11:22:45.594291+02:00"
}

Identity

  • key — canonical identifier built from the owning node's key and the prefix in CIDR notation.
  • safe-id — an HTML/URL-safe variant of the key.
  • instance-id — the BGP-LS Instance Identifier the prefix belongs to. Same as the domain.
  • node-key — the key of the node advertising this prefix. Look it up under Nodes.

Prefix data

  • prefix — the CIDR string (e.g. 10.1.1.1/32, fcdd:dd00:1::/48).
  • prefix-length — the prefix length as an integer.
  • ip-version — 4 or 6.
  • ospf-route-type — OSPF route type when learned through OSPF (omitted otherwise).
  • metric — the IGP metric advertised for this prefix.

SR-MPLS Prefix SIDs

If the prefix carries SR-MPLS Prefix SIDs (RFC 8667), the export includes an sr-mpls.prefix-sids array. Each entry has:

  • index — the SID index from the IGP.
  • sid — the computed MPLS label (index + SRGB base of the advertising node).
  • algorithm — 0 plain SPF, 1 Strict-SPF, 128–255 Flex-Algo.
  • flags — a decoded view of the Prefix-SID flag byte:
Flag Field name Meaning
R re-advertisement The prefix was redistributed from another scope.
N node-sid The prefix identifies the node itself (typically a loopback).
P no-php The penultimate hop must not pop the label.
E explicit-null Replace the label with explicit null before forwarding.
V value The SID is an absolute label, not an index into the SRGB.
L local The SID is local to the advertising node.
— raw The raw flag byte, useful for cross-checking against router CLI output.

SRv6 locator metadata

When the prefix is advertised as an SRv6 locator (rather than as a plain IGP prefix), the export includes an srv6 block with the locator-specific metadata:

  • sid-structure — the four-field breakdown (LBL/LNL/FL/AL), same shape as on End.X SIDs (see Links / SRv6).
  • endpoint-behavior — the IANA-registered behavior code for SIDs programmed under this locator.
  • endpoint-behavior-name — the human-readable behavior name (End, End (PSP/USP), End (USD), Flex-Algo variants, …).
  • algorithm — the SR algorithm the locator serves.
  • flags — raw locator flag byte from the SRv6 SID NLRI.
  • multi-topo-ids — Multi-Topology IDs the locator is bound to, when applicable.

Source peers and last update

  • source-peers — the list of BGP-LS speakers currently contributing this prefix.
  • last-update — timestamp of the most recent change.
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