Hello. Today i switched over from radvd to dnsmasq RA but when I try to access any Microsoft website it fails to resolve over ipv6 (i think it eventually falls back to ipv4 and resolves after 30+ secs). Changing the RA MTU in DNSmasq from default (1500?) to 1492, to match my WAN MTU (Calculated PPP MTU) fixes this problem.
So my question is am I correct in thinking DNSmasq RA MTU should match the WAN MTU or are my assumptions wrong here.
Thanks for any help.
IPv6 MTU is way smaller than IPv4. Leave it at default or set it to 40 bytes less than your IPv4 MTU.
Ok, thanks meyergru. Leaving it blank (default) gives me issues with Microsoft websites. I would be interested in knowing what the default MTU value is but I'm unable to find any such documentation.
And since dnsmasq dhcp will be the default option for most home networks going forward I think it would be helpful if there was at least a note in the opnsense docs regarding this. Unless I've just run into a bug.
Ah, so you only got problems because of PPPoE. Yes, you should use the same MTU as on WAN, because if you do not clamp your MSS, you may experience problems with sites that have defect PMTUD.
You can also try this (https://forum.opnsense.org/index.php?topic=45658.0) - but only if your ISP supports mini jumbo frames... if that works, you can use the "usual" 1500 byte MTU and problems as this will be resolved. There is no 100% guarantee, though.
Thanks very much for the pointers, I will go through it thoroughly tomorrow.