T_X<p>At <span class="h-card" translate="no"><a href="https://chaos.social/@ffhl" class="u-url mention" rel="nofollow noopener" target="_blank">@<span>ffhl</span></a></span> we have asymmetric <a href="https://chaos.social/tags/IPv6" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>IPv6</span></a> routes, too: <span class="h-card" translate="no"><a href="https://chaos.social/@ffhl" class="u-url mention" rel="nofollow noopener" target="_blank">@<span>ffhl</span></a></span> -> <span class="h-card" translate="no"><a href="https://chaos.social/@FreifunkHamburg" class="u-url mention" rel="nofollow noopener" target="_blank">@<span>FreifunkHamburg</span></a></span> -> ... -> <a href="https://chaos.social/tags/Microsoft" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>Microsoft</span></a>. And: <a href="https://chaos.social/tags/Microsoft" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>Microsoft</span></a> -> ... -> <span class="h-card" translate="no"><a href="https://social.ffmuc.net/@freifunkMUC" class="u-url mention" rel="nofollow noopener" target="_blank">@<span>freifunkMUC</span></a></span> -> <1480 <a href="https://chaos.social/tags/MTU" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>MTU</span></a> <a href="https://chaos.social/tags/GRE" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>GRE</span></a> tunnel> -> <span class="h-card" translate="no"><a href="https://chaos.social/@ffhl" class="u-url mention" rel="nofollow noopener" target="_blank">@<span>ffhl</span></a></span>.</p><p>With network namespaces I recreated the asymmetric routes with differing MTUs on my laptop behind a DSL. I see my virtual router on my laptop send ICMPv6 Packet Too Big packets. But Microsoft keeps sending too big packets. So with that I seem to be able to recreate the issue without the Freifunk context.</p>