[outages] HE IPv6 tunnel PMTU issues with juniper.net

[Chuck Anderson]

On Wed, Oct 01, 2014 at 02:17:01PM +0000, Gary Gapinski via Outages wrote:
> On 10/01/2014 01:50 PM, Chuck Anderson via Outages wrote:
> >While on my Hurricane Electric IPv6 tunnel, I cannot access
> >juniper.net unless I change my local interface MTU.  1500 fails, but
> >1280 works.  I noticed this a few days ago.  Before that I had no
> >problems with a 1500 MTU.  Is anyone else seeing this issue?
> 
> No, but if your are using a 6in4 tunnel, the MTU should be 1480 (not 1500).
> 
> (I just successfully went to www.juniper.net via IPv6 with that MTU 1480.)

My tunnel router has a 1280 MTU on the henet interface:

6in4-henet Link encap:IPv6-in-IPv4  
          inet6 addr: 2001:470:xxxx:xxxx::2/64 Scope:Global
          inet6 addr: fe80::xxxx:xxxx/128 Scope:Link
          UP POINTOPOINT RUNNING NOARP  MTU:1280  Metric:1
          RX packets:17148418 errors:0 dropped:0 overruns:0 frame:0
          TX packets:12347808 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:2660258163 (2.4 GiB)  TX bytes:2833651623 (2.6 GiB)

But the LAN interface of that router has an MTU of 1500, as does my
desktop system.  I believe the issue is that the juniper.net web
server has an MTU of 1500 and their network or somewhere along the
path is blocking ICMP Packet Too Big messages that would be sent by
the HE.net tunnel router.

Like I said, I changed nothing on my end, and it was working before.
I don't know if juniper.net just added IPv6 to their website, or if
something else changed in the path.