MTU problem

[Morcos]

Hello all,
I was trying to change the MTU size by running the command lanadmin and it worked with me on the first server, but when i was trying to change the MTU on the 2nd server I was receiving an error message:unable to change MTU size errno=22.
Even when trying to change MTU from sam, the same problem persists.

Regards,
Ziad

[Peter Godron · Accepted solution]

Ziad,
what are you trying to set it to ?
It may be a range limit problem.

Please list lanadmin command .

[Sunil Sharma_1]

Ziad,

It is possible that the one value specified for one lan card may not work with other. The MTU value range depend on type of card you are using.

You can set it with lanadmin -M

Sunil

[Morcos]

Thx Peter for your quick answer.
Well I'm trying to set the MTU to 500.

The output of Lanadmin is:
PPA Number = 0
Description = lan0 HP PCI Core I/O 1000Base-T Release B.11.
1.21
Type (value) = ethernet-csmacd(6)
MTU Size = 1500
Speed = 100000000
Station Address = 0x14c210d2d9
Administration Status (value) = up(1)
Operation Status (value) = up(1)
Last Change = 403658437
Inbound Octets = 3745791373
Inbound Unicast Packets = 401768101
Inbound Non-Unicast Packets = 59107825
Inbound Discards = 20037
Inbound Errors = 0
Inbound Unknown Protocols = 20053536
Outbound Octets = 2079284204
Outbound Unicast Packets = 434106130
Outbound Non-Unicast Packets = 17722
Outbound Discards = 0
Outbound Errors = 0
Outbound Queue Length = 0
Specific = 655367


thx in advanced.

ziad

[Peter Godron]

Ziad,
I don't think you can set the MTu on this card to 500.
From:
docs.hp.com/en/J5683-90002/J5683-90002.pdf

"1000Base-T features:
â Triple speed 10/100/1000 Mbps
â Full duplex operation at 10/100/1000 Mbps and half-duplex operation at 10/100
Mbps (no half-duplex support for 1000 Mbps)
â Autonegotiation and autosensing to the highest available link speed"

"â ¢ Maximum Transmission Unit (MTU)
The MTU can be either the regular Ethernet MTU (1500 bytes) or the Jumbo Frame
MTU (9000 bytes). For 1000Base-T, jumbo frames can be configured only when the
link speed is 1000 Mbps."

[Steve Lewis]

What you might be able to do is to effectively set the MTU by re-specifying the default route with a PMTU.

See man route
The -p parameter is the one to use.

Don't do it on the same lan that you are connected through, or else do this on the console. Otherwise you may be disconnected.

[rick jones]

PathMTU may indeed be the best way to go here. It does beg the question though - why do you want to cripple your NICs with a 500 byte MTU?