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

[Gary Gapinski]

On 10/01/2014 05:58 PM, Chuck Anderson via Outages wrote:
> The Linux "/sbin/ip" command apparently can show mtu and advmss (as 
> seen in Google search results), but on my system it doesn't show them. 
> cat /proc/sys/net/ipv6/conf/<interface>/mtu does show it though. 

Ditto mine (proc/sys/net/ipv6/conf/<interface>/mtu is 1480). ip does not 
cough up MTU.

> Right. If you turn off the AdvLinkMTU option (or set it back to 1500) 
> such that the initial SYN sets an MSS of 1440, do you then have 
> problems reaching www.juniper.net?

No, which is a bit puzzling. WIth MTU at 1500 on LAN interface, TCP 
connect had outbound SYN with MSS 1420, return SYN ACK with MSS 1420. No 
related ICMPv6 seen. This was tried from a LAN device, not the edge 
router (i.e., the one with the tunnel).