I have few questions for better understanding of usage: if check sum is 0 it will be updated or left as zero.
if check sum is some wrong value (i.e. packet was modified), what is expected? if check sum is valid and this feature supported only in software, what is expected? Maxim. On 28 March 2017 at 15:28, Savolainen, Petri (Nokia - FI/Espoo) < petri.savolai...@nokia-bell-labs.com> wrote: > > > > -----Original Message----- > > From: Bill Fischofer [mailto:bill.fischo...@linaro.org] > > Sent: Tuesday, March 28, 2017 3:05 PM > > To: Savolainen, Petri (Nokia - FI/Espoo) <petri.savolainen@nokia-bell- > > labs.com> > > Cc: lng-odp-forward <lng-odp@lists.linaro.org> > > Subject: Re: [lng-odp] [API-NEXT PATCH] api: packet: add per packet > > checksum control > > > > On Tue, Mar 28, 2017 at 6:39 AM, Savolainen, Petri (Nokia - FI/Espoo) > > <petri.savolai...@nokia-bell-labs.com> wrote: > > > It's a mandatory feature when forwarding: "Forwarded packets need to > > maintain original, end-to-end checksum value.". A box in the middle must > > not re-compute e.g. L4 checksum. If it would do that, it could introduce > > an error in payload data and update the checksum accordingly. The > > receiving end would not notice the error, since checksum matches. > > > > If the middle box can't be trusted not to tamper with the payload when > > forwarding, why would you trust it not to "cover its tracks" by > > recomputing checksums, or remember to call this API? End-to-end > > integrity is why protocols like IPsec are used. > > > > L4 checksums are end-to-end, not per link. L4 checksum protects e.g. > against memory errors in mid boxes (switches and routers). What would be > the point of having a per link L4 checksum? Link layer has CRC/checksum per > link already. Is this use case clear now ? > > -Petri >
