[AusNOG] Upstream PMTUD broken? Packets blackhole

[Mark Newton]

On Sep 14, 2016, at 12:34 AM, s.s.o.n.i.k+a.u.s.n.o.g at gmail.com wrote:
> Client firewall MTU set to 1484: Successful reply at length 1456. Unsuccessful at 1457, however echo request is seen, and unreachable 3:4 message is returned by firewall, but never arrives at the source.

Ethernet firewall? Why is the MTU so low?

These problems are virtually always caused by a firewall blocking ICMP. Usually it’s a firewall operated by the person who is complaining about PMTUD not working :-)

  - mark


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ausnog.net/pipermail/ausnog/attachments/20160914/56d48326/attachment.html>