[Edited Message Follows] Hi experts,
I am confusing about the L4 checksum behavior in VPP. I noticed the code was there for a very long time(more than 3 years) so I open this topic to see if anybody knows the history and why. * The first problem is in DPDK plugin and was introduced in commit d81566ff92: Disable for-us udp/tcp checksum validation by default in Current DPDK plugin, the code clears flags VNET_BUFFER_F_L4_CHECKSUM_COMPUTED and VNET_BUFFER_F_L4_CHECKSUM_CORRECT when "enable-tcp-udp-checksum" option is enabled. While these two flags are used to identify if the L4 checksum is checked and correct, respectively. So I think this is a wrong behavior - *are we doing the opposite* ? The current DPDK plugin assumes all the packets from DPDK are correct but in fact we should check per packet and set the corresponding bits. I've pushed a patch to fix this issue and Dave invited experts to help to review - Thanks Dave :-) * Another problem in the IP4 graph node. The following mechanism was first introduced in commit 96be8e88109b3e1 and got refactored in commit 1b25552eb. #define ip4_local_csum_is_offloaded(_b) \ _b->flags & VNET_BUFFER_F_OFFLOAD_TCP_CKSUM \ || _b->flags & VNET_BUFFER_F_OFFLOAD_UDP_CKSUM #define ip4_local_need_csum_check(is_tcp_udp, _b) \ (is_tcp_udp && !(_b->flags & VNET_BUFFER_F_L4_CHECKSUM_COMPUTED \ || ip4_local_csum_is_offloaded (_b))) #define ip4_local_csum_is_valid(_b) \ (_b->flags & VNET_BUFFER_F_L4_CHECKSUM_CORRECT \ || (ip4_local_csum_is_offloaded (_b))) != 0 In my understanding, the Marcos ip4_local_need_csum_check and ip4_local_csum_is_valid are used to check if the L4 checksum is computed and checked before ip4-local node. While the Macro ip4_local_csum_is_offloaded is to check if the L4 checksum can be offloaded to NIC on the *TX side*. *I am not very clear why do we need to check the tx offload capability in the RX path* - maybe we are expecting the NIC can help to re-calculate the checksum before sending out? Think about if an APP(local APP running upon TCP/UDP stack or a tunnel like VxLAN/GTPU/etc...) is running on L4, it would get invalid checksum packets(Considering the DPDK plugin marked all the packets are COMPUTED and CORRECT as I described in the first problem). see in: commit 96be8e88109b3e166b76f58e552dbe438d73bb73 Author: Jakub Grajciar <jakub.grajc...@pantheon.tech> Date: Mon Oct 30 14:56:17 2017 +0100 vnet: ip4/6_local->don't drop packet if marked for TCP/UDP offload cksum calculation
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