PPPoE RFC4638 problem. Not seeing 1500 MTU on pppoe-client?

RouterOS General
1

Hello,

So this is my setup:

pppoe server <—> switch <—> mikrotik pppoe client

pppoe server (linux pppd):

  • supports rfc4638
  • eth0 supports jumbo frames
  • eth0 mtu set to 1508
  • eth0.10 mtu set to 1508
  • pppoe server enabled on eth0.10 (vlan 10)

switch:

  • jumbo frames support enabled

mikrotik pppoe client:

  • tested on hap lite, rb2011
  • tested version 6.34.4 and 6.35.rc48
/interface ethernet
set [ find default-name=ether1 ] mtu=1508

/interface vlan
add interface=ether1 mtu=1508 name=ether1.10 vlan-id=10

/interface pppoe-client
add add-default-route=yes allow=chap disabled=no interface=ether1.10\
    max-mru=1500 max-mtu=1500 name=pppoe-out1 password=test123 use-peer-dns=yes \
    user=testme

pppoe server established connection:

ppp1    Link encap:Point-to-Point Protocol
          inet addr:10.10.10.1  P-t-P:10.10.10.100  Mask:255.255.255.255
          UP POINTOPOINT RUNNING  MTU:1500  Metric:1
          RX packets:7074 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5572 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:8106361 (7.7 MiB)  TX bytes:374636 (365.8 KiB)

mikrotik pppoe client established connection:

          status: connected
          uptime: 15m17s
    active-links: 1
        encoding: 
    service-name: 
         ac-name: test-pppoe
          ac-mac: 6C:B3:11:3B:25:BA
             mtu: 1480
             mru: 1500
   local-address: 10.10.10.100
  remote-address: 10.10.10.1

As you can see, the MTU is set to 1480 on the pppoe client. If I set max-mtu=1492 in the pppoe-client I get then mtu of 1492, but any bigger than that it sets itself to 1480 after connecting.

Pppoe server on the other hand correctly sets up a MTU 1500 tunnel.

tcpdump from pppoe-server during client connection:
http://pastebin.com/AEycU5xc

In the tcpdump both the server and client set PPP-Max-Payload tag of 1500 (RFC 4638) and both client and server advertise MRU of 1500 in the LCP packets. Yet Mikrotik doesn’t set the MTU to 1500 after the connection is established.

Was anyone successful in getting RFC4638 to work on Mikrotik?. It seems to be supported (since 6.33) but I didn’t manage to find an example.

Thank you.

2

It works for me, but I have only the client to worry about and I set the MTU of ether1 to 1598 (same as max).

3

Hmm, no matter what I try it falls back to MTU 1480 on the pppoe-client. Could you post your settings? (Shouldn’t be much) would appreciate it.

4

/interface ethernet
set [ find default-name=ether1 ] mtu=1598 name=eth1-vdsl
/interface pppoe-client
add add-default-route=yes allow=pap,mschap2 default-route-distance=1 disabled=no
interface=eth1-vdsl max-mru=1500 max-mtu=1500 mrru=1500 name=
pppoe-xs4all-inet password=XXXX user=XXXX

5

Thank you. So it’s basically the same. I will keep on trying.

6

I can’t get more than 1492 too. Some news here?

7

We’re experiencing the exact same issue… The other end supports baby jumbo frames of 1508, however the Miktrotik will let us put in 1500 however after a few seconds of the connection going to live, it reverts back to 1480.

I’m at a point now where I don’t bother contacting support, as they just fob you off with they’re aware of it and it will be fixed at some point.

8

Also with MikroTik at both ends, or when using a MikroTik router as a client for your ISP?
The latter is what I have: MikroTik router connected via Draytek 130 VDSL modem running as PPPoE relay
to ISP using Juniper router to terminate the PPPoE circuit, and supporting RFC4638. It works OK (MTU/MRU 1500).
This appears to indicate the client side works OK. Maybe not the server side?