MTU for PPPoE

RouterOS General
1

By default rOS set 1480 for PPPoE interfaces and add a mangle rule to modify the TCP segment size, i want to set 1500 (full ip packet) to improve performance and remove this mangle rule, all the network is able to support it.

This is the setup:

PPPoE server:

add default-profile=defaultMTU1500noTCP_MSS disabled=no interface=ether4 max-mru=1500 max-mtu=1500 \
    one-session-per-host=yes service-name=internet

Default profile:

add change-tcp-mss=no local-address=192.168.200.1 name=defaultMTU1500noTCP_MSS remote-address=\
    PPPoE_pool

PPPoE client:

/interface pppoe-client
add add-default-route=yes disabled=no interface=ether1 name=pppoe-out1 service-name=internet use-peer-dns=yes user=pruebaMTU

As you can see no MTU is defined on PPPoE client and i set 1500MTU on the server… but anyway the PPPoE clients still connecting with MTU and MRU 1480.

I dont want to log in in each of the CPE’s to setup the MTU field.

The configuration which im showing is on test environment just a cable between a RB750 and a CCR. Running 6.35.2

2
  1. all interfaces that this tunnel cross ( router, server, and switches in between need to be configured to at least 1550 MTU (i would go to 1600 just in case) only then packet that have 1500 bytes + pppoe header will be able to travel your network without fragmentation.

This topic is good place to get the understanding:
http://wiki.mikrotik.com/index.php?title=Manual:Maximum_Transmission_Unit_on_RouterBoards

so in your test you need to configure phywical interface MTU and L2MTU

3

I know… So, this is my problem, all network is configured to handle it but if i dont configure it on pppoe client it doesnt work … and i just want to configure it on server and restart the connections and leave the MTU on clients in auto mode.

My frames are like:

[14 physical ethernet | 8 double MPLS | 4 VPLS | 14 encapsulated ethernet | 8 PPPoE | 1500 IP+Payload]

Maybe its rOS bug or something i dont know, because on the lab scenario its just most simply case [ethernet + pppoe + ip…] and its also not working.

4

Someone?

5

  1. have you changed MTU of all interfaces that participate in PPPoE tunel transition to 1600 ??? (client server, all switches/bridges in between?

  2. have you specified MTU 1500 and MRU 1500 both in pppoe-client and in pppoe-server?

If both done, you will not have any change-mss rule in mangle cause it will be unnecessary

6

Did it, if i set 1500 on client interface is working … but i really dont want to logging in each CPE… so what im trying is set the MTU values in pppoe server but its not working CPE’s keep connecting witch 1480 when the MTU field on the client is disabled…

Whatever seems the only way will be do it one by one… :confused: