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

[Chuck Anderson]

On Wed, Oct 01, 2014 at 03:16:10PM +0000, Gary Gapinski via Outages wrote:
>     On 10/01/2014 02:37 PM, Chuck Anderson
>       wrote:
> 
>       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.
> 
>     Perhaps, though IMO unlikely.
> 
>     I too have a LAN MTU of 1500, and have a (HE.net) tunnel MTU of
>     1480. I do not see any PMTU problems to www.juniper.net or
>     elsewhere.
> 
>     However, I am explicitly advertising MTU 1480 in LAN RAs.

Interesting.  Does the 1480 MTU setting from RA show up on your
interface configuration, or in a routing table entry?  Is your TCP
connection to www.juniper.net using an MSS of 1220?  If so, then of
course you wouldn't see the issue.

I'm using OpenWRT for the HE.net tunnel.  I'll have to see how to send
the MTU in the LAN RA.

>     Here is a partial outbound route from my origin:
> 
>     gapinski at eins:~$ traceroute -6 -A www.juniper.net
> traceroute to www.juniper.net (2600:1408:17:293::720), 30 hops max, 80 byte packets
>  …
>  3  ge3-4.core1.chi1.he.net (2001:470:0:6e::1) [AS6939]  43.778 ms  43.892 ms  43.876 ms
>  4  twcable-backbone-as7843.10gigabitethernet1-1-6.switch3.chi1.he.net (2001:470:0:2bb::2) [AS6939]  55.905 ms  55.988 ms  55.983 ms
>  5  2001:1998:0:4::171 (2001:1998:0:4::171) [AS7843]  39.962 ms 2001:1998:0:4::ed (2001:1998:0:4::ed) [AS7843]  40.635 ms 2001:1998:0:4::171 (2001:1998:0:4::171) [AS7843]  42.125 ms
>  6  2001:1998:0:4::a3 (2001:1998:0:4::a3) [AS7843]  63.789 ms  49.818 ms 2001:1998:0:4::b1 (2001:1998:0:4::b1) [AS7843]  50.215 ms
>  7  2001:1998:0:4::80 (2001:1998:0:4::80) [AS7843]  54.505 ms 2001:1998:0:4::a4 (2001:1998:0:4::a4) [AS7843]  55.892 ms 2001:1998:0:4::80 (2001:1998:0:4::80) [AS7843]  55.006 ms
>  8  2001:1998:0:4::5c (2001:1998:0:4::5c) [AS7843]  57.100 ms  57.060 ms  58.693 ms
>  9  2001:1998:0:4::90 (2001:1998:0:4::90) [AS7843]  56.811 ms  57.152 ms 2001:1998:0:4::86 (2001:1998:0:4::86) [AS7843]  57.956 ms
> 10  2001:1998:0:4::f4 (2001:1998:0:4::f4) [AS7843]  55.055 ms 2001:1998:0:4::1a1 (2001:1998:0:4::1a1) [AS7843]  55.153 ms 2001:1998:0:4::f4 (2001:1998:0:4::f4) [AS7843]  55.107 ms
> 11  2001:1998:0:8::2c6 (2001:1998:0:8::2c6) [AS7843]  56.198 ms  56.771 ms  55.622 ms
> 12  2600:1408:17::17dc:947c (2600:1408:17::17dc:947c) [AS20940]  49.388 ms  59.963 ms  60.354 ms
> gapinski at eins:~$

Traceroute from here:

traceroute to www.juniper.net (2600:141b:4:2a2::720), 30 hops max, 80 byte packets
 1  2001:470:xxxx:1::1 (2001:470:xxxx:1::1)  0.327 ms  0.328 ms  0.352 ms
 2  2001:470:xxxx:xxxx::1 (2001:470:xxxx:xxxx::1)  19.155 ms  22.996 ms  26.192 ms
 3  ge3-8.core1.nyc4.he.net (2001:470:0:5d::1)  27.735 ms  28.878 ms  28.996 ms
 4  v6-paix-ny.3-2.r1.ny.hwng.net (2001:504:f::4c)  29.094 ms  28.999 ms  29.070 ms
 5  2001:4de0:1000:64::2 (2001:4de0:1000:64::2)  29.069 ms * *
 6  * 2001:4de0:2001:8::2 (2001:4de0:2001:8::2)  23.048 ms  23.912 ms
 7  2600:141b:4::48f7:acf (2600:141b:4::48f7:acf)  23.960 ms  16.420 ms *