.. _example_protocols_bgp_neighbor_update-source:

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Update-Source
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Scenario to verify BGP **neighbor update-source** functionality.
The update-source command specifies which interface's IP address to use
as the source address for BGP sessions. This test uses a loopback/dummy
interface as update-source, which is a common pattern for BGP stability -
if a physical interface fails but alternative routes exist, the session survives.

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Test iBGP - Session establishes without update-source using direct interface
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Description
===========

Test to verify that without **update-source**, BGP uses the outgoing interface IP
as the source address. DUT0 peers with DUT1's directly connected address (10.10.0.200),
and DUT1 expects connections from DUT0's directly connected address (10.10.0.100).
Both peers use their physical interface IPs, so the session establishes normally without
needing update-source.

Scenario
========

.. include:: update-source/testibgp-sessionestablisheswithoutupdate-sourceusingdirectinterface

.. raw:: html

  <hr>

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Test iBGP - Neighbor update-source with loopback
************************************************

Description
===========

Test BGP **neighbor update-source** with a loopback/dummy interface.
DUT0 uses update-source to set its dummy interface (2.2.2.100) as the source
address for BGP packets. DUT1 is configured to peer with that loopback IP and has
a static route to reach it. The update-source command is necessary here because DUT1
expects connections from 2.2.2.100, not from the physical interface IP.
This pattern provides BGP session stability - if the physical link fails but alternative
routes exist to the loopback, the session can survive.

Scenario
========

.. include:: update-source/testibgp-neighborupdate-sourcewithloopback

.. raw:: html

  <hr>