IPv6 day and tunnels

Joe Maimon jmaimon at ttec.com
Tue Jun 5 07:21:36 CDT 2012

Owen DeLong wrote:

> But that's a whole lot more packets than working PMTU-D to get there and
> you're also waiting for all those round trips, not just the 4 timeouts.
> The round trips add up if you're dealing with a 100ms+ RTT. 22 RTTs at
> 100ms is 2.2 seconds. That's a long time to go without first data packet
> passed,
> Owen

Yes, it is quite nice when ICMP helpfully informs you what your MTU is.

However, we have known for quite some time that is simply not reliable 
on the IPv4 internet, for a multitude of reasons, with intentional ICMP 
blocking just one of them.

I have no reason to expect it to work better in IPv6.

This is why more reliable methods are a good idea, even if they work 
slower or add more overhead, because as I see it they are intended to be 
used concurrently with ICMP.

Also, as I understand the probing, getting data through happens much 
faster then arriving at the optimal mtu size might take.

Perhaps short flows should just be sticking to the min-mtu anyways.


More information about the NANOG mailing list