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Old 8th March 2009
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schrodinger schrodinger is offline
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Default Jumbo Frames

Hi all,

I have a firewall with a vge0 interface doing firewalling/routing between Gigabit VLANs. I am trying to configure the mtu of the interface to support larger frames.

The NIC is a VIA VT6122

According to the vge man page:

The MAC supports IPv4 transmit/receive IP/TCP/UDP hardware
checksum offload, VLAN tag insertion and stripping, a 64-entry CAM filter
and a 64-entry VLAN filter, 64-bit multicast hash filter, 4 separate
transmit DMA queues, flow control and Jumbo frames up to 16K in size.
The VT6122 has a 16K receive FIFO and 48K transmit FIFO.
No matter what I try though I can't seem to change the MTU. I always get

"ifconfig: SIOCSIFMTU: Invalid argument"

What are the valid sizes for the MTU value? I want to set it to a max of 9K as that is the largest frame size my switch will support.

Also does one change the MTU on the real interface or the VLAN interface?
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