[ewg] IPoIB to Ethernet routing performance

Roland Dreier rdreier at cisco.com
Fri Dec 17 09:24:05 PST 2010

 >   This may be due to the fact that the IB MTU is 2048. Every 1500 bytes packet
 > is padded to 2048 bytes before being sent through the wire, so you're loosing
 > roughly 25% bandwidth compared to an IPoIB MTU which is a multiple of 2048.

This isn't true.  IB packets are only padded to a multiple of 4 bytes.

However there's no point in using IPoIB connected mode to pass packets
smaller than the IB MTU -- you might as well use datagram mode.

 - R.

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