Changing MTU size

glb...@netins.net

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Sep 16, 2008, 4:05:37 PM9/16/08

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I try to send a raw socket packet size of 1600 and get the following
message. I can send 1500 sizes ok.

Send failed - Errno: 90

My ifconfig shows

emac2: flags=8a43<UP,BROADCAST,RUNNING,ALLMULTI,SIMPLEX,MULTICAST> mtu
1500
inet 172.16.1.107 netmask 0xffff0000 broadcast 172.16.255.255
ether 00:17:3c:00:32:b6

Thanks
Gary

Steve Watt

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Sep 16, 2008, 5:34:23 PM9/16/08

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In article <b2c0ec5a-0fa8-4c74...@m45g2000hsb.googlegroups.com>,

"ifconfig emac2 mtu <number>"?

Note that many controllers don't support frames larger than 1518, and
changing the MTU setting has many interoperability side effects.
--
Steve Watt KD6GGD PP-ASEL-IA ICBM: 121W 56' 57.5" / 37N 20' 15.3"
Internet: steve @ Watt.COM Whois: SW32-ARIN
Free time? There's no such thing. It just comes in varying prices...

glb...@netins.net

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Sep 17, 2008, 9:35:45 AM9/17/08

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Yes... I tried ifconfig emac2 mtu 1514 but 'mtu' is not
supported in LynxOS .

glb...@netins.net

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Sep 18, 2008, 9:21:27 AM9/18/08

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On Sep 17, 8:35 am, glbl...@netins.net wrote:
> Yes... I tried ifconfig emac2 mtu 1514 but 'mtu' is not
> supported in LynxOS .
>
>
>
> Steve Watt wrote:

> > In article <b2c0ec5a-0fa8-4c74-bd17-272805062...@m45g2000hsb.googlegroups.com>,

> > <glbl...@netins.net> wrote:
> > >I try to send a raw socket packet size of 1600 and get the following
> > >message. I can send 1500 sizes ok.
>
> > >Send failed - Errno: 90
>
> > >My ifconfig shows
>
> > >emac2: flags=8a43<UP,BROADCAST,RUNNING,ALLMULTI,SIMPLEX,MULTICAST> mtu
> > >1500
> > > inet 172.16.1.107 netmask 0xffff0000 broadcast 172.16.255.255
> > > ether 00:17:3c:00:32:b6
>
> > "ifconfig emac2 mtu <number>"?
>
> > Note that many controllers don't support frames larger than 1518, and
> > changing the MTU setting has many interoperability side effects.
> > --
> > Steve Watt KD6GGD PP-ASEL-IA ICBM: 121W 56' 57.5" / 37N 20' 15.3"
> > Internet: steve @ Watt.COM Whois: SW32-ARIN

> > Free time? There's no such thing. It just comes in varying prices...- Hide quoted text -
>
> - Show quoted text -

Yes i've tried the ifconfig emac2 mtu 1514 but 'mtu' is not
supported in LynxOS.
I can send a 1600 byte packet via a regular socket, just not the raw
one..

Gary

Steve Watt

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Sep 18, 2008, 5:36:47 PM9/18/08

to

In article <af06a825-596d-4d57...@k30g2000hse.googlegroups.com>,
<glb...@netins.net> wrote:
[ quoting repaired ]

> Steve Watt wrote:
> > In article <b2c0ec5a-0fa8-4c74-bd17-272805062...@m45g2000hsb.googlegroups.com>,
> > <glbl...@netins.net> wrote:
> > >I try to send a raw socket packet size of 1600 and get the following
> > >message. I can send 1500 sizes ok.

[ ... ]

> > >My ifconfig shows
>
> > >emac2: flags=8a43<UP,BROADCAST,RUNNING,ALLMULTI,SIMPLEX,MULTICAST> mtu
> > >1500
> > > inet 172.16.1.107 netmask 0xffff0000 broadcast 172.16.255.255
> > > ether 00:17:3c:00:32:b6

> > "ifconfig emac2 mtu <number>"?

> > Note that many controllers don't support frames larger than 1518, and
> > changing the MTU setting has many interoperability side effects.
>

>Yes i've tried the ifconfig emac2 mtu 1514 but 'mtu' is not
>supported in LynxOS.

The MTU parameter is certainly supported in LynxOS. It may not be
supported by whatever driver underlies 'emac2'.

To verify, try "ifconfig emac2 mtu 500". If that works, then 1500
is the maximum MTU that hardware supports.

>I can send a 1600 byte packet via a regular socket, just not the raw
>one..

Yes, because a regular socket (assuming you mean IP with either TCP
or UDP) has upper-level support for segmentation or fragmentation,
respectively.

glb...@netins.net

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Sep 19, 2008, 10:14:46 AM9/19/08

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On Sep 18, 4:36 pm, Steve Watt <steve.removet...@Watt.COM> wrote:

> Free time? There's no such thing. It just comes in varying prices...- Hide quoted text -
>
> - Show quoted text -

hmmmm

ifconfig emac2 mtu 500
ERROR: ioctl (set mtu): Invalid argument

My driver may not support it. What does the driver change
specifically if we added an mtu to it ?

Gary

stef

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Sep 22, 2008, 5:56:28 AM9/22/08

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the following two ioctls need to be supported by the intervace
driver:
SIOCGIFMTU -> get current MTU
SIOCSIFMTU -> set new MTU

very few lynx interface driver does support thes ioctls. em (intel
pro1000) does support it

S.