Re: [Fwd: I-D ACTION:draft-lear-multi6-things-to-think-about-00.txt]

[Iljitsch van Beijnum <iljitsch@muada.com>]

On 18-dec-03, at 21:12, Eliot Lear wrote:

> (hopefully) the document contains some questions that can be used to 
> evaluate such minor issues as deployability, security, performance, 
> and generality.

:-)

I found another one: TCP and UDP checksum calculation offloading. It 
seems this is pretty common these days: I have a box with a turn of the 
century NIC and FreeBSD tells me it is offloading both rx and tx 
checksums. (It works too: dire tcpdump warnings when running verbose 
enough as outgoing packets have invalid checksums as seen by BPF.)

With any multihoming solution that allows rewriting of addresses 
between the moment the checksum calculation is done and the moment the 
packet is transmitted/received, checksum offloading will pretty much 
have to be a thing of the past, unless we want to start doing some 
complex incremental updating in different places.

So which is preferable? Keep it simple but lose hardware support for 
checksumming, or keep hardware support but add more complexity?

Note that the processing for the TCP/UDP checksum is simple enough that 
it's probably free when doing a memcopy anyway.