[AusNOG] Upstream PMTUD broken? Packets blackhole

[Jonathan Brewer]

Hope you figure it out! One thought is to do with passing traffic through IX

On 14 September 2016 at 02:34, <s.s.o.n.i.k+a.u.s.n.o.g at gmail.com> wrote:

> It feels like an MTU issue, or overzealous ICMP 3:4 filtering.
>
>
>
> I’ve done as much testing and investigation as I can do, and the every
> ISPs has pointed to the cause of the problem being with their Tier 1 / Tier
> 2 providers. Traceroute from affected customers pass through Vocus or
> Telstra, and seem to all pass through IXs in NSW. If I’m lucky the traces
> complete, but “request timed out” *** often shows up where it should not.
>

If there's a change in MTU at the IX, you may have trouble. IX IP address
space is often not globally routable, so an ICMP response coming from a
router using that address space can be lost.

Cheers,

Jon
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