On 26.11, Pablo Neira Ayuso wrote: > On Thu, Nov 26, 2015 at 09:54:45AM +0000, Patrick McHardy wrote: > > On 26.11, Pablo Neira Ayuso wrote: > > > > > ToS breaks useful things like ECN, and the more I keep reading docs on > > > > > the Internet, the more problem I have to see how the user can benefit > > > > > from this. > > > > > > > > We *match* on ToS, that cannot possibly break anything. Also I'm unsure how > > > > this could break ECN even otherwise, ToS does not even use the ECN bits. > > > > > > ToS bits overlap with ECN bits, from that original ToS 8 bit-field now > > > we use 6 bit for DSCP and 2 bits for ECN. > > > > Sure, but our ToS definition is wrong anyway, the ToS-bits are actually > > 3 + 3 + 2 unused bits (ECN). > > That's right according to the original ToS definition, but looking a > bit further on the RFCs, someone outthere extended this, so I found > this: > > See 22. Historical Definitions for the IPv4 TOS Octet from > https://tools.ietf.org/html/rfc3168. > > It refers to https://tools.ietf.org/html/rfc1349 that defines > Minimize Monetary Cost TOS Value and it extends it to one extra bit > (from 3 to 4, scratching one from the unused bits). > > Bottom line says "Because of this unstable history, the definition of > the ECN field in this document cannot be guaranteed to be backwards > compatible with all past uses of these two bits." > > Anyway, looking at the Linux header definitions, we have the > > #define IPTOS_MINCOST 0x02 > > The mincost thing is there. > > #define IPTOS_TOS_MASK 0x1E > #define IPTOS_TOS(tos) ((tos)&IPTOS_TOS_MASK) > > So it seems our headers are considering ToS is 4 bits too. Hmm Ok its really a mess. Let's get rid of it for now and we might reconsider if a user turns up that can make a valid case. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
