Hi, Le mercredi 18 novembre 2015 à 12:46 +0200, Yuval Shaia a écrit : > On Thu, Jul 30, 2015 at 03:58:13PM +0200, Yann Droneaud wrote: > > Le jeudi 30 juillet 2015 à 04:46 -0700, Yuval Shaia a écrit : > > > This enhancement suggest the usage of IB CRC instead of CSUM in > > > IPoIB CM. IPoIB CM uses RC (Reliable Connection) which guarantees > > > the corruption free delivery of the packet. > > > > > > InfiniBand uses 32b CRC which provides stronger data integrity > > > protection compare to 16b IP Checksum. > > > > InfiniBand 32b CRC <=> Ethernet 32b CRC, it's link layer, layer 2. > > > > IPv4 checksum is at another level, it's internet layer, layer 3. > > > > > So, there is no added value that IP/TCP Checksum provides in the > > > IB world. > > > > > > > Sure, IPv4 checksum is a thing of the past: checksum was dropped > > from IP header in IPv6: it assumes the lower layer, such as > > Ethernet, provides the required integrety check. > Right, will change description to something like this: > InfiniBand 32b CRC offers strong data integrity protection compare > CSUM. This patch must clearly state that, without IPv4 header checksum, it's no more IP protocol as described by RFC 791 > > > > I think not checking the IPv4 checksum should be a choice, > > carefully thought, for inside a fabric, as I understand your > > proposal, packet with invalid checksum will be allowed to go in/out > > of the fabric. > If peer supports this feature do you see any reason why not? You're free to run you own protocol inside your private network, but this protocol is not compatible with IPv4. > > > > It sound like it's a departure from the behavior one can expect > > from an IPv4 network stack. > > > > > The proposal is to tell network stack that IPoIB-CM supports IP > > > Checksum offload. This enables the kernel to save the time of > > > checksum calculation of IPoIB CM packets. Network sends the IP > > > packet without adding the IP Checksum to the header. On the > > > receive side, IPoIB driver again tells the network stack that IP > > > Checksum is good for the incoming packets and network stack > > > avoids the IP Checksum calculations. > > > > > > During connection establishment the driver determine if peer > > > supports IB CRC as checksum. This is done so driver will be able > > > to calculate checksum before transmiting the packet in case the > > > peer does not support this feature. > > > > > > > Two questions: > > > > - What will see tool such as wireshark/tcpdump when sniffing > > checksum-less IPv4 packets sent/received on IPoIB interface ? > Never checked it but i assume 0 or what ever the kernel put there > when driver reports NETIF_F_IP_CSUM. I can check and zero if needed > but any reason to believe it is needed? I don't think it's needed if you agree that this modification creates a new protocol which is no more IPv4. > > > > - What might happen if such checksum-less IPv4 packet is later > > routed to a different IPv4 network ? > Same as my question above, if peer supports this feature do you see > anything wrong? If peer is going to forward this packet to a different network, which is not IPoIB based, the checksum will be checked and the packet will be rejected. Regards. -- Yann Droneaud OPTEYA -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
