.. _example_protocols_bgp_neighbor_addpath:

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Addpath
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.. sidebar:: Contents

  .. contents::
    :depth: 2
    :local:

Scenario to verify BGP **neighbor addpath** functionality.
By default, BGP only advertises the single best path for each prefix to its
neighbors. The addpath feature allows the router to advertise multiple paths,
giving the receiving peer visibility of alternative routes for its own path
selection. The ``addpath-tx-all-paths`` option advertises **all** available paths
for a prefix to the neighbor. The ``addpath-tx-bestpath-per-AS`` option provides
a middle ground by advertising only the **best path from each originating AS**.

The topology uses three routers: **DUT1** (AS 200) announces ``1.1.1.0/24`` to
**DUT0** (AS 100), which also has the same prefix locally via a dummy interface.
**DUT0** then advertises to **DUT2** (AS 300). The test verifies three scenarios:

- **Baseline** (no addpath): DUT2 receives only **1 path** (the best path selected
  by DUT0). Addpath TX is not advertised on the neighbor.

- **addpath-tx-all-paths**: DUT2 receives **2 paths** — one from AS 100 (DUT0 local)
  and one from AS 100 200 (from DUT1 via DUT0). Addpath TX is advertised.

- **addpath-tx-bestpath-per-AS**: DUT2 receives **2 paths** — the best path from
  each originating AS. Addpath TX is advertised.

.. image:: addpath.svg
  :width: 400

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Test eBGP - Neighbor addpath modes
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Description
===========

Test addpath modes on a neighbor: without addpath (baseline, 1 path),
with ``addpath-tx-all-paths`` (2 paths), and with ``addpath-tx-bestpath-per-AS`` (2 paths).

Scenario
========

.. include:: addpath/testebgp-neighboraddpathmodes

.. raw:: html

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