MTU Problem: Akamai,HE,GTT

Erik Nygren erik at
Mon Sep 22 16:06:49 CEST 2014

Can you pass me along a traceroute6 to 2a02:26f0:6a:18f::eed and I'll pass
it along to the Akamai NOCC?  (Or you can email details to noc at
>From here I'm able to ping it fine with large packets:

$ ping6 -s 1452 2a02:26f0:6a:18f::eed
PING 2a02:26f0:6a:18f::eed(2a02:26f0:6a:18f::eed) 1452 data bytes
1460 bytes from 2a02:26f0:6a:18f::eed: icmp_seq=1 ttl=52 time=105 ms
1460 bytes from 2a02:26f0:6a:18f::eed: icmp_seq=2 ttl=52 time=105 ms
1460 bytes from 2a02:26f0:6a:18f::eed: icmp_seq=3 ttl=52 time=106 ms
1460 bytes from 2a02:26f0:6a:18f::eed: icmp_seq=4 ttl=52 time=105 ms

Are any of the others Akamai IPs that you're having problems with?  While
we have intentionally not lowered our initial MSS (we don't want a broken
Internet where ICMPv6 PMTUD doesn't work), we very rarely hear of issues
and almost all of them end up being last-mile misconfigurations near the


On Mon, Sep 22, 2014 at 5:16 AM, Ignatios Souvatzis <ignatios at
> wrote:

> Hi,
> for at least one seems to hang most of the time for
> some of my users. The reason is javascript code unconditionally loaded
> from
> is an alias for
> is an alias for
> has IPv6 address 2a02:26f0:6a:191::eed
> has IPv6 address 2a02:26f0:6a:18f::eed
> The latter two networks (or at least one of them) seem to block
> IPv6 packets of too large a size.
> I get replies to ICMPv6 echo requests with PING6(1280=40+8+1232 bytes)
> but not bigger; I suspect an icmpv6 black hole somwehere.
> However, some others show the same problem.
> Working (addresses shortened):
> 2001:638:a000:: (fully inside DFN), but also
> 2a00:19e0::
> 2001:608::
> 2001:200::
> so I think it's not a problem with two DFN internal tunnels I'm aware of
> (one inside Univ. of Bonn, one the UoB's next hop).
> Not working:
> 2001:470::              (routed through
> 2001:1900:2254::        (routed through
> 2a02:26f0:6a::          (routed through
> I can workaround on my workgroup edge router, but I guess it would be
> more helpful if the real problem would be fixed.
> Regards,
>         Ignatios Souvatzis
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