<p><a href="https://arxiv.org/pdf/1811.03716.pdf" rel="nofollow noreferrer">https://arxiv.org/pdf/1811.03716.pdf</a> has a description</p>

<p>Summary:</p>

<ul>
<li><p>Say router Rdst wants to influence the path that inbound traffic takes, say for example traffic from router Rsrc to router Rdst.</p></li>
<li><p>Say the shortest path from Rsrc to Rdst goes through some intermediate router Rint.</p></li>
<li><p>Let's say router Rdst in autonomous system ASdst, router Rsrc is autonomous system ASsrc, router Rint is in autonomous system ASint, etc. (see figure below)</p></li>
<li><p>In particular, router Rdst wants to enforce that the traffic does <em>not</em> go through router Rint but instead takes some longer route, for example through some alternative routers Ralt1 and Ralt2 (once again, see figure below).</p></li>
<li><p>To achieve this, router Rdst "poisons" its routes when it sends out BGP advertisements for its own destination prefix:</p>

<ul>
<li><p>Instead of advertising the normal AS-path (ASdst), it instead advertises (ASdst, ASint, ASdst).</p></li>
<li><p>Note that Rdst is "lying": it claims that the path already went through ASint, when in fact it didn't.</p></li>
<li><p>It also adds an extra ASdst to make sure that the first AS in the AS-path still looks normal (= the AS of the advertising router).</p></li>
<li><p>When Rint receives the BGP UPDATE advertised by Rdst, it will see that there is a loop in the AS-path and treat the UPDATE as a withdraw. In particular, not propagate the advertisement to Rsrc.</p></li>
<li><p>On the other hand, the BGP advertisement will propagate normally from Rdst to Ralt1 to Ralt2 to Rsrc.</p></li>
<li><p>Hence, from the perspective of Rsrc, the only remaining feasible path is Rsrc -> Ralt2 -> Ralt1 -> Rdst.</p></li>
</ul></li>
<li><p>Ergo: Rdst has achieved its goal of forcing the traffic to avoid Rint.</p></li>
</ul>

<pre>

          Rdst (ASdst)
     ____/    \_____
    /               \
Ralt1 (ASalt1)      Rint (ASint)
   |                 |
Ralr2 (ASalt2)       |
    \____       ____/
         \     /
          Rsrc (ASsrc)
</pre>
What exactly is "BGP poisoning"?
<p>I found statements "BGP poisoning" and "poisoned AS" in several papers and sometimes it seems to refer to something that is done the achieve a certain thing sometimes it is considered something bad but it is never explained what exactly "BGP poisoning" actually is. </p>

<p>As I wasn't able to find an answer to this question myself I would appreciate if you could provide me your understanding of the concept.</p>