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From
SubjectRe: ifconfig eth0 mtu 2000: SIOCSIFMTU: Invalid argument
Date
Followup to:  <Pine.LNX.3.95.961103080752.266A-100000@mikeg.weiden.de>
By author: "Michael L. Galbraith" <mikeg@mikeg.weiden.de>
In newsgroup: linux.dev.kernel
>
> Hello Everyone,
>
> I tried to adjust the mtu on an interface with the result:
> SIOCSIFMTU: Invalid argument

Care to specify what kernel version you're using?

> No interface (except lo) can be set to an mtu of over 1500 period.
> Did I miss something?
> Rules change on me? I used to be able to go up to 4096-header.

No, a bug was fixed. 1500 is the maximum MTU for Ethernet.

> It got a lot more interesting when Mr. Speedtypist here missed the
> "mtu" part. I inadvertently entered "ifconfig eth0 2000", with the
> following result:
>
> Nov 3 07:53:53 mikeg kernel: Unable to handle kernel paging request
> at virtual address f63a3336

Now this is a pretty serious kernel bug. "ifconfig eth0 2000" should
be interpreted as 0.0.7.208; I don't know why that barfed -- seems
pretty serious. On my system (2.0.20) it worked flawlessly; with the
expected result:

eth0 Link encap:10Mbps Ethernet HWaddr 00:A0:24:19:2F:71
inet addr:0.0.7.208 Bcast:10.7.9.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:343514 errors:0 dropped:0 overruns:0
TX packets:390530 errors:0 dropped:0 overruns:0
Interrupt:10 Base address:0x300

Ifconfig-ing back to the original address worked just fine; didn't
even lose my TCP connections (good thing, too, as I'm writing this
message over one of them.)

-hpa

--
Not speaking for Transmeta in any shape, way, or form.


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