.. _example_protocols_bgp_neighbor_attribute-unchanged:

###################
Attribute-Unchanged
###################

Test BGP **attribute-unchanged** functionality. This command prevents the router from
modifying specific BGP attributes when advertising routes to a neighbor. By default,
when advertising to an eBGP peer, the router changes the next-hop to its own address,
prepends its AS number to the AS-path, and may modify the MED value. The attribute-unchanged
command allows preserving these attributes in their original form. The **as-path** option
prevents the router from prepending its local AS to the path. The **med** option preserves
the Multi-Exit Discriminator value without modification. The **next-hop** option keeps the
original next-hop address instead of replacing it with the advertising router's address.
This feature is typically used with eBGP multihop peers in scenarios like MPLS inter-AS.

.. image:: 3duts.svg
  :width: 800

********************************************************************
Test eBGP - Default behavior modifies attributes on re-advertisement
********************************************************************

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

Baseline test showing default eBGP re-advertisement behavior. DUT1 (AS 200)
originates 1.1.1.0/24. DUT0 (AS 100) receives and forwards to DUT2 (AS 300)
without attribute-unchanged. DUT2 should see next-hop changed to DUT0's IP and
AS-path prepended with AS 100.

Scenario
========

.. include:: attribute-unchanged/testebgp-defaultbehaviormodifiesattributesonre-advertisement

.. raw:: html

  <hr>

***************************************
Test eBGP - Attribute-unchanged as-path
***************************************

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

Verify that **attribute-unchanged as-path** prevents DUT0 from prepending its AS
when re-advertising routes. DUT0 forwards to DUT2 without adding AS 100 to the path.

Scenario
========

.. include:: attribute-unchanged/testebgp-attribute-unchangedas-path

.. raw:: html

  <hr>

****************************************
Test eBGP - Attribute-unchanged next-hop
****************************************

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

Verify that **attribute-unchanged next-hop** preserves the original next-hop
when re-advertising routes. DUT0 forwards to DUT2 keeping DUT1's IP as next-hop,
but AS-path is still prepended with DUT0's AS.

Scenario
========

.. include:: attribute-unchanged/testebgp-attribute-unchangednext-hop

.. raw:: html

  <hr>

***********************************
Test eBGP - Attribute-unchanged med
***********************************

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

Verify that **attribute-unchanged med** preserves the MED value when
re-advertising routes. DUT1 sets MED 50 and DUT2 should see it unchanged.

Scenario
========

.. include:: attribute-unchanged/testebgp-attribute-unchangedmed

.. raw:: html

  <hr>