MTU Problem

Hello, i have vlan on vlan interface, i meen
interface vlan add interface ether1 vland-id=12 name=vlan1
interface vlan add interface vlan1 vland-id=13

on vlan13 i have dhcp server, on vlan12 i have pppoe server.

on vlan13 users cannot access internet, they cannot open some site.

I did so
i removed change mms from pppoe profile and add static rule

ip firewall mangel add chan=forwared in. interface all-vlan protocol=tcp change-mss=1480
ip firewall mangel add chan=forwared out. interface all-vlan protocol=tcp change-mss=1480

now they can access internet.

is this correct?

I have about 1500 pppoe users and 500 mbps traffic.
device is ccr.
Thank you

Yes, that will work.

Because you are decrementing the frame size by 4bytes for each vlan tag, plus the extra for PPPoE.

I would actually suggest lowering it a little more, we have always found 1440~ works best.