Re: MTU 1640

The default MTU, size of 1500-byte MTU, or somewhat smaller is sufficient be=
cause Ethernet frames are limited to a standard maximum of 1500 bytes of pay=
load data. Various IEEE standards use expanded frame sizes to carry addition=
al information. Don't spend to much time with the MTU size at first. Verify w=
hat are the speed and duplex settings and actually check the results first, b=
efore troubleshooting layer 3 and 4 issues. Well, this is my 2c from dealing=
 with PPPoE/VPN issues in the past. Another test you can run, once connected=
, is to change the MTU size from the command line and see at what value does=
 an ping fails when modifying the MTU size/value. You will notice if you mak=
e the MTU size to small, the ping will fail/timed out. Troubleshooting MTU s=
ize and fragmented packers are really hard to figure out. Wireshark will add=
 some light to the works, depending "where" you you capture the network traf=
fic. (Encrypted vs unencrypted) Hope this info will put you on the right tra=
ck.=20

> On Dec 26, 2014, at 3:12 AM, Jakob Schwienbacher track<jakob.schwienbacher=
@gmail.com> wrote:
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> Hi,
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> Im running M0n0wall 1.8.1. Im using PPPoE to connect to my ISP. I had some=

> trouble with MTU size, then i saw my WAN MUT is set to 1460:
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> $ ifconfig
> ~
> ngwan0: flags=3D88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> metri=
c 0
> mtu 1460
> ~
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> 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 and=

> in the config file also after a reboot.
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> $ cat /var/etc/mpd.conf
> startup:
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> pppoe:
> create bundle static B1
> ~
> set link mtu 1492
> ~
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> 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.
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> 1. Does anybody see the same issue?
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> 2. Someon know about the value 1460? I couldn't find anything about that.
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> Thanks in advance,
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> Jakob