MTU and VLAN

[Kafkaesque]

Hey guys

Question about MTU settings and my Bell Canada WTTH internet. I did some packet tests and discovered that the largest packet I can send without fragmenting is 1412 (ugh). So I know that to set MTU properly you are supposed to add 28 to that for the headers which would take me to 1440.

However I am also sending a VLAN tag because it's bell internet which is another 4. So......do I set my MTU to 1440 or 1444? I have read conflicting reports, some that say add it and some that say it's ignored in the MTU (that is the MTU would accept 1440 OR 1444 if I set it at 1440). I know it's not a big deal in the grand scheme of things but I'm more curious than anything.

Appreciate the help!

EDIT: So last night I set it to 1440 and everything seems to be working okay except that wireless seems a little slow to respond at first. Pages load quickly, speedtest is good once the connection is made. Any input? Have I achieved anything at all or is this just pointless anyway lol.

[Lantis]

It's not something I've ever really learned about. There's a very helpful guy on the OpenWrt forums called moeller who seems to know a lot about it. May be worth posting there or sending him a message.

[Kafkaesque]

Excellent. I may give him a try then. FYI everything seemed to be working okay and then completely went south just a bit ago. WAN connected with a public IP but no internet (as if the VLAN tag was gone) however I checked and it was still there so makes me wonder if the tags were getting dropped although it would seem strange to happen after 24 hours.

I enjoy playing with stuff like this, keeps my mind fresh at my age. The kids don't enjoy the internet going up and down as I play. Oh well, that's the power you get when you're a parent

[Kafkaesque]

Okay so the guys at OpenWRT are pointing me towards the MTU_FIX switch like this:

config zone
option name wan
list network 'wan'
list network 'wan6'
option input REJECT
option output ACCEPT
option forward REJECT
option masq 1
option mtu_fix 1

Now I'm assuming this option exists in Gargoyle so I would insert it like this....?

config interface 'wan'
option proto 'dhcp'
option ipv6 '0'
option macaddr 'XXXXXXXXXXXX'
option ifname 'eth0.35'
option mtu '1444'
option mtu_fix '1'

config device 'wan_dev'
option name 'eth0.35'

config interface 'wan6'
option ifname 'eth0.35'
option proto 'dhcpv6'
option mtu_fix '1'

However it still doesn't seem to answer my original question of 1440 vs 1444 lol. But I am trying 1444 as you can see above to see what happens.

[Lantis]

Not quite. that mtu_fix goes in the firewall zone config for Wan, not the network interface.

[Kafkaesque]

And it was already there lol. Thanks for the push in the right direction.