# Problems setting right MTU in /etc/conf.d/net

## merlijn

For some reason it seems the mtu_eth0 setting has no effect in my case, I want to have it at 9000 for my home gigabit lan. Everytime I reboot it prompts the message "Given MTU 64 is too low, setting MTU to 576". Hrm, didnt i say 9000?

/etc/conf.d/net

```

modules=( "ifconfig" )

config_eth0=( "dhcp" )

mtu_eth0="9000"

```

DHCP comes from my rather old adsl router, which only has a 100 mbit connection to the gigabit switch' uplink.

Any input would be much appreciated.

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## steveb

It could be that your NIC does not allow 9000 (jumbo frames) or your router/switch/whatever. What NIC are you using?

// SteveB

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## merlijn

Thank you for your reply.

The card is an onboard controller based on Realtek RTL8111B. I always thought 9000 as mtu was the standard for gigabit connectors (or the standard maximum to put it better) isn't jumbo frames mtu 15000 for gigabit?

I am not very sure about my network equipment. The switch is fully gigabit capable and should handle every mtu, but the router is old and shitty, and is based on only 10/100mbit ethernet, how would this affect the mtu settings?

Cheers,

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## steveb

 *merlijn wrote:*   

> The card is an onboard controller based on Realtek RTL8111B. I always thought 9000 as mtu was the standard for gigabit connectors (or the standard maximum to put it better) isn't jumbo frames mtu 15000 for gigabit?

 Okay. You have a problem. The RTL8111B does indeed support jumbo frames but the driver included in the stock Kernel has a problem with it (not only with jumbo frames. Even normal 1500 MTU can be a problem with the driver in the stock Kernel). You need to go to Realtek web page and download the driver from there and patch your current Kernel with it. This will allow you to set jumbo frames.

 *merlijn wrote:*   

> I am not very sure about my network equipment. The switch is fully gigabit capable and should handle every mtu, but the router is old and shitty, and is based on only 10/100mbit ethernet, how would this affect the mtu settings?

 This can affect MTU settings. You need to check if your router supports jumbo frames. If it does not support jumbo frames then check if it supports baby frames (this is around 6000 MTU).

Check here for the working driver.

// SteveB

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