Ipv6 unusable due lack of love from FreeBSD (prev: Support baby jumbo frames)

hda

Using native ipv6 over PPPoE.

Not only have PPPoE WAN on 1492, but LAN on 1492 too, for RA. Then MSS is 1432 for IPv6. Test with wireshark and see the MSS 1440 when you leave LAN MTU on 1500 (or blank ?).

M_Devil

Need to put LAN on MTU=1492 because of RA? I use Jumbo frames (MTU=9000) on LAN side. No problems at all with ipv4. Not sure if I understand your suggested test, but I give it a try.

doktornotor

@hda: Not needed at all on any PPPoE box I tried.

@M_Devil: With the jumbo nonsense, you're on a sure way to a giant kaboom, which has totally nothing to do with this topic.

M_Devil

@doktornotor mtu change on LAN side was suggested by hda. Because I did not see the relevance for changing MTU on LAN side, I did mention my use of jumbo for LAN side (for inter vlan routing).

hda

My native IPv6 connection isn't comfortable (ISP IPv6 lease renewal fails) with MTU=1492 & MSS=1472 only on WAN & all 'blank' on LAN's. I concluded the common denominator MTU=1492 for IPv6, as long as MTU negotiation (rfc4638) doesn't work everywhere or flawlessly. Found out MTU=1492 & 'blank' MSS for all interfaces with IPv6 works best or reliable.

@M_Devil: RA advertizes the MTU=xxxx in its broadcast.

M_Devil

@hda thank you for the clarification.

Running MTU and MSS settings like you suggested and running fine. Can only hope pfSense/FreeBSD team can solve the root cause in a reasonable amount of time.

Harvy66

I may be missing something, but I found some reference on https://calomel.org/freebsd_network_tuning.html

With an interface MTU of 1500 bytes we suggest an
net.inet.tcp.mssdflt of 1460 bytes. 1500 MTU minus 20 byte IP header minus 20
byte TCP header is 1460. With net.inet.tcp.rfc1323 enabled, tcp timestamps
are added to the packets and the mss is automatically reduced from 1460 bytes
to 1448 bytes total payload. Note: if you are using PF with an outgoing scrub
rule then PF will re-package the data using an MTU of 1460 by default, thus
overriding this mssdflt setting

It sounds like PF scrub doesn't adjust for rfc1323, so you need to manually set your MSS to 1448?

doktornotor

It suggests to set net.inet.tcp.mssdflt which is not what the MSS setting does in the GUI. Plus it tells you that it will be ignored completely by scrub, so no idea really what's the point in messing with net.inet.tcp.mssdflt here.

Harvy66

I guess what I was getting at is it ignores the default setting. The term "default" implies the value can be changed. Instead of using the default values, why not manually set the values?

doktornotor

Dunno, but "scrub rule then PF will re-package the data using an MTU of 1460 by default, thus overriding this mssdflt setting" would strongly suggest that messing with that sysctl is a total waste of time.