On Wed, Oct 01, 2014 at 07:01:59PM +0000, Gary Gapinski via Outages wrote:
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).
I /think/ you may have to flush your routing table after changing MTU--it seems the route cache maintains the per-destination MTU/MSS. At one point I saw some extra routes with MTU 1280 in "/sbin/ip -6 route show".