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diff --git a/Documentation/networking/nf_flowtable.txt b/Documentation/networking/nf_flowtable.txt deleted file mode 100644 index ca2136c76042..000000000000 --- a/Documentation/networking/nf_flowtable.txt +++ /dev/null @@ -1,112 +0,0 @@ -Netfilter's flowtable infrastructure -==================================== - -This documentation describes the software flowtable infrastructure available in -Netfilter since Linux kernel 4.16. - -Overview --------- - -Initial packets follow the classic forwarding path, once the flow enters the -established state according to the conntrack semantics (ie. we have seen traffic -in both directions), then you can decide to offload the flow to the flowtable -from the forward chain via the 'flow offload' action available in nftables. - -Packets that find an entry in the flowtable (ie. flowtable hit) are sent to the -output netdevice via neigh_xmit(), hence, they bypass the classic forwarding -path (the visible effect is that you do not see these packets from any of the -netfilter hooks coming after the ingress). In case of flowtable miss, the packet -follows the classic forward path. - -The flowtable uses a resizable hashtable, lookups are based on the following -7-tuple selectors: source, destination, layer 3 and layer 4 protocols, source -and destination ports and the input interface (useful in case there are several -conntrack zones in place). - -Flowtables are populated via the 'flow offload' nftables action, so the user can -selectively specify what flows are placed into the flow table. Hence, packets -follow the classic forwarding path unless the user explicitly instruct packets -to use this new alternative forwarding path via nftables policy. - -This is represented in Fig.1, which describes the classic forwarding path -including the Netfilter hooks and the flowtable fastpath bypass. - - userspace process - ^ | - | | - _____|____ ____\/___ - / \ / \ - | input | | output | - \__________/ \_________/ - ^ | - | | - _________ __________ --------- _____\/_____ - / \ / \ |Routing | / \ - --> ingress ---> prerouting ---> |decision| | postrouting |--> neigh_xmit - \_________/ \__________/ ---------- \____________/ ^ - | ^ | ^ | - flowtable | ____\/___ | | - | | / \ | | - __\/___ | | forward |------------ | - |-----| | \_________/ | - |-----| | 'flow offload' rule | - |-----| | adds entry to | - |_____| | flowtable | - | | | - / \ | | - /hit\_no_| | - \ ? / | - \ / | - |__yes_________________fastpath bypass ____________________________| - - Fig.1 Netfilter hooks and flowtable interactions - -The flowtable entry also stores the NAT configuration, so all packets are -mangled according to the NAT policy that matches the initial packets that went -through the classic forwarding path. The TTL is decremented before calling -neigh_xmit(). Fragmented traffic is passed up to follow the classic forwarding -path given that the transport selectors are missing, therefore flowtable lookup -is not possible. - -Example configuration ---------------------- - -Enabling the flowtable bypass is relatively easy, you only need to create a -flowtable and add one rule to your forward chain. - - table inet x { - flowtable f { - hook ingress priority 0 devices = { eth0, eth1 }; - } - chain y { - type filter hook forward priority 0; policy accept; - ip protocol tcp flow offload @f - counter packets 0 bytes 0 - } - } - -This example adds the flowtable 'f' to the ingress hook of the eth0 and eth1 -netdevices. You can create as many flowtables as you want in case you need to -perform resource partitioning. The flowtable priority defines the order in which -hooks are run in the pipeline, this is convenient in case you already have a -nftables ingress chain (make sure the flowtable priority is smaller than the -nftables ingress chain hence the flowtable runs before in the pipeline). - -The 'flow offload' action from the forward chain 'y' adds an entry to the -flowtable for the TCP syn-ack packet coming in the reply direction. Once the -flow is offloaded, you will observe that the counter rule in the example above -does not get updated for the packets that are being forwarded through the -forwarding bypass. - -More reading ------------- - -This documentation is based on the LWN.net articles [1][2]. Rafal Milecki also -made a very complete and comprehensive summary called "A state of network -acceleration" that describes how things were before this infrastructure was -mailined [3] and it also makes a rough summary of this work [4]. - -[1] https://lwn.net/Articles/738214/ -[2] https://lwn.net/Articles/742164/ -[3] http://lists.infradead.org/pipermail/lede-dev/2018-January/010830.html -[4] http://lists.infradead.org/pipermail/lede-dev/2018-January/010829.html |