Re: MTU 1640

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Did you try to leave the MTU field blank. That should default to 1492 bytes f=
or PPPoE.=20


> On Dec 26, 2014, at 6:31 AM, Jakob Schwienbacher <jakob.schwienbacher@gmai=
l.com> wrote:
>=20
> Hello Johan,
>=20
> Thank you for the response. In fact everything works fine at my site. The p=
oint is why do I have MTU size of 1460 instead of 1492 (1492 =3D 1500 defaul=
t MTU - 8 Byte PPPoE Header). Furthermore I cannot change in the MTU Size in=
 the UI of monowall (I can change but it doesn`t take effect).
>=20
> A ping gives following result:
>=20
> $ ping x.x.x.x -M do -s 1432
> PING x.x.x.x (x.x.x.x) 1432(1460) bytes of data.
> 1440 bytes from x.x.x.x: icmp_seq=3D1 ttl=3D59 time=3D46.1 ms
> 1440 bytes from x.x.x.x: icmp_seq=3D2 ttl=3D59 time=3D37.9 ms
> 1440 bytes from x.x.x.x: icmp_seq=3D3 ttl=3D59 time=3D35.5 ms
> 1440 bytes from x.x.x.x: icmp_seq=3D4 ttl=3D59 time=3D37.2 ms
>=20
> --- x.x.x.x ping statistics ---
> 4 packets transmitted, 4 received, 0% packet loss, time 601ms
> rtt min/avg/max/mdev =3D 35.522/39.213/46.193/4.127 ms
> $
>=20
> $ ping x.x.x.x -M do -s 1433
> PING x.x.x.x (x.x.x.x) 1433(1461) bytes of data.
> ping: local error: Message too long, mtu=3D1460
> ping: local error: Message too long, mtu=3D1460
> ping: local error: Message too long, mtu=3D1460
> ping: local error: Message too long, mtu=3D1460
>=20
> --- x.x.x.x ping statistics ---
> 4 packets transmitted, 0 received, +4 errors, 100% packet loss, time 608ms=

>=20
> Thank you,
>=20
> Jakob
>=20
>> On 26 December 2014 at 11:18, Johan Vanderwesthuizen <[email protected]=
t> wrote:
>> The default MTU, size of 1500-byte MTU, or somewhat smaller is sufficient=
 because Ethernet frames are limited to a standard maximum of 1500 bytes of p=
ayload data. Various IEEE standards use expanded frame sizes to carry additi=
onal information. Don't spend to much time with the MTU size at first. Verif=
y what are the speed and duplex settings and actually check the results firs=
t, before troubleshooting layer 3 and 4 issues. Well, this is my 2c from dea=
ling with PPPoE/VPN issues in the past. Another test you can run, once conne=
cted, is to change the MTU size from the command line and see at what value d=
oes an ping fails when modifying the MTU size/value. You will notice if you m=
ake the MTU size to small, the ping will fail/timed out. Troubleshooting MTU=
 size and fragmented packers are really hard to figure out. Wireshark will a=
dd some light to the works, depending "where" you you capture the network tr=
affic. (Encrypted vs unencrypted) Hope this info will put you on the right t=
rack.
>>=20
>> > On Dec 26, 2014, at 3:12 AM, Jakob Schwienbacher track<jakob.schwienbac=
[email protected]> wrote:
>> >
>> > Hi,
>> >
>> > Im running M0n0wall 1.8.1. Im using PPPoE to connect to my ISP. I had s=
ome
>> > trouble with MTU size, then i saw my WAN MUT is set to 1460:
>> >
>> > $ ifconfig
>> > ~
>> > ngwan0: flags=3D88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> me=
tric 0
>> > mtu 1460
>> > ~
>> >
>> > I went to Interfaces > WAN and set the MTU to 1492 (which should be the=

>> > Maximum possible on PPPoE links). The MTU setting is visible on the UI a=
nd
>> > in the config file also after a reboot.
>> >
>> >
>> > $ cat /var/etc/mpd.conf
>> > startup:
>> >
>> > pppoe:
>> > create bundle static B1
>> > ~
>> > set link mtu 1492
>> > ~
>> >
>> > I disconnected and reconected my WAN interface, I did a reboot of my
>> > m0n0wall. But the MTU doesn`t get changed. It remains on 1460.
>> >
>> > 1. Does anybody see the same issue?
>> >
>> > 2. Someon know about the value 1460? I couldn't find anything about tha=
t.
>> >
>> >
>> > Thanks in advance,
>> >
>> > Jakob
>=20

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