Message destination host unreachable from default gateway
<p>I have some <em>PCs (win) + server + network printers</em> all connected to the same switch and all configured in the same <em>subnet</em>.</p>

<blockquote>
  <p>When the switch is not connected to the uplink everything works fine
  (my office is isolated from the rest of the world). But when we
  connect the uplink (to other switches) we have random packet loss.</p>
</blockquote>

<p>If I ping my subnet  (my PC's!!!) I get random temporary messages "<strong>destination host unreachable</strong>" replied from my default gateway (???), but if I ping outside my subnet I have no packet loss. When I'm getting the "<strong>host unreachable message</strong>" in my ARP table I see the default gateway MAC address at the IP that I'm pinging (???).</p>

<p>What's going on? Thanks</p>