[RP-PPPoE] PPPoE MTU problem

[Wenzhuo Zhang]

Hi, Dianne

Here is my dd-wrt pppd options file /tmp/ppp/options.pppoe:
-------------------------------------
plugin /usr/lib/rp-pppoe.so

nic-vlan2
noccp
nomppc
noipdefault
noauth
defaultroute
noaccomp
nobsdcomp
nodeflate
nopcomp
nomppe
usepeerdns
user 'username'
password 'password'
default-asyncmap
mtu 1492
mru 1492
persist
lcp-echo-interval 3
lcp-echo-failure 20
-------------------------------------

How do I fix it?

Also, I configured PPPoE connections using Network Manager in Ubuntu
14.04 and 16.04 in exactly the same way. The MTU of the ppp interface
created in Ubuntu 14.04 (ppp-2.4.5) is 1492, whereas it's 1442 in
Ubuntu 16.04 (ppp-2.4.7).

Wenzhuo

On Mon, Feb 22, 2016 at 8:00 PM, Dianne Skoll <dfs at roaringpenguin.com> wrote:
> On Mon, 22 Feb 2016 10:15:21 +0800
> Wenzhuo Zhang <wenzhuo at gmail.com> wrote:
>
>> The PPPoE Access Concentrator of my ISP offers MRU values of both 1492
>> and 1442. ppp-2.4.5 in Ubuntu 14.04 adopts 1492 as the MTU of the ppp
>> device, while ppp-2.4.7 in Ubuntu 16.04 (xenial developement) adopts
>> 1442. Choosing the lower MTU on the WAN link (ppp0) exposes users to
>> the nasty PMTU-D problem, especially for remote VPN clients. I also
>> reproduced the same problem in openwrt 15.05 and dd-wrt r29085, both
>> of which come with ppp-2.4.7.
>
> That's not a PPPoE problem.  It's a pppd misconfiguration; you can
> easily fix it in the pppd config file.
>
> Regards,
>
> Dianne.
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