X-Git-Url: http://git.cascardo.info/?p=cascardo%2Fovs.git;a=blobdiff_plain;f=FAQ.md;h=8bd7ab9190332934b24f015f39db2c811522b813;hp=512bd2cdfe8fc5ef971f875126459ce0c68f98bf;hb=HEAD;hpb=fdce83a304da56255474c7be68232fd4d4edcf41 diff --git a/FAQ.md b/FAQ.md index 512bd2cdf..8bd7ab919 100644 --- a/FAQ.md +++ b/FAQ.md @@ -156,7 +156,7 @@ A: The following table lists the Linux kernel versions against which the | 2.1.x | 2.6.32 to 3.11 | 2.3.x | 2.6.32 to 3.14 | 2.4.x | 2.6.32 to 4.0 -| 2.5.x | 2.6.32 to 4.2 +| 2.5.x | 2.6.32 to 4.3 Open vSwitch userspace should also work with the Linux kernel module built into Linux 3.3 and later. @@ -165,6 +165,73 @@ A: The following table lists the Linux kernel versions against which the It should build against almost any kernel, certainly against 2.6.32 and later. +### Q: Are all features available with all datapaths? + +A: Open vSwitch supports different datapaths on different platforms. Each + datapath has a different feature set: the following tables try to summarize + the status. + + Supported datapaths: + + * *Linux upstream*: The datapath implemented by the kernel module shipped + with Linux upstream. Since features have been gradually + introduced into the kernel, the table mentions the first + Linux release whose OVS module supports the feature. + + * *Linux OVS tree*: The datapath implemented by the Linux kernel module + distributed with the OVS source tree. Some features of + this module rely on functionality not available in older + kernels: in this case the minumum Linux version (against + which the feature can be compiled) is listed. + + * *Userspace*: Also known as DPDK, dpif-netdev or dummy datapath. It is the + only datapath that works on NetBSD and FreeBSD. + + * *Hyper-V*: Also known as the Windows datapath. + + The following table lists the datapath supported features from + an Open vSwitch user's perspective. + +Feature | Linux upstream | Linux OVS tree | Userspace | Hyper-V | +----------------------|:--------------:|:--------------:|:---------:|:-------:| +Connection tracking | 4.3 | 3.10 | NO | NO | +Tunnel - LISP | NO | YES | NO | NO | +Tunnel - STT | NO | 3.5 | NO | YES | +Tunnel - GRE | 3.11 | YES | YES | YES | +Tunnel - VXLAN | 3.12 | YES | YES | YES | +Tunnel - Geneve | 3.18 | YES | YES | NO | +QoS - Policing | YES | YES | NO | NO | +QoS - Shaping | YES | YES | NO | NO | +sFlow | YES | YES | YES | NO | +Set action | YES | YES | YES | PARTIAL | +NIC Bonding | YES | YES | YES | NO | +Multiple VTEPs | YES | YES | YES | NO | + + **Notes:** + * Only a limited set of flow fields is modifiable via the set action by the + Hyper-V datapath. + * The Hyper-V datapath only supports one physical NIC per datapath. This is + why bonding is not supported. + * The Hyper-V datapath can have at most one IP address configured as a + tunnel endpoint. + + The following table lists features that do not *directly* impact an + Open vSwitch user, e.g. because their absence can be hidden by the ofproto + layer (usually this comes with a performance penalty). + +Feature | Linux upstream | Linux OVS tree | Userspace | Hyper-V | +----------------------|:--------------:|:--------------:|:---------:|:-------:| +SCTP flows | 3.12 | YES | YES | YES | +MPLS | 3.19 | YES | YES | YES | +UFID | 4.0 | YES | YES | NO | +Megaflows | 3.12 | YES | YES | NO | +Masked set action | 4.0 | YES | YES | NO | +Recirculation | 3.19 | YES | YES | NO | +TCP flags matching | 3.13 | YES | YES | NO | +Validate flow actions | YES | YES | N/A | NO | +Multiple datapaths | YES | YES | YES | NO | +Tunnel TSO - STT | N/A | YES | NO | YES | + ### Q: I get an error like this when I configure Open vSwitch: configure: error: Linux kernel in is version , but @@ -448,7 +515,7 @@ A: The following commands configure br0 with eth0 and tap0 as trunk To later disable mirroring and destroy the GRE tunnel: ovs-vsctl clear bridge br0 mirrors - ovs-vcstl del-port br0 gre0 + ovs-vsctl del-port br0 gre0 ### Q: Does Open vSwitch support ERSPAN? @@ -564,6 +631,32 @@ A: Open vSwitch has two kinds of flows (see the previous question), so A: Open vSwitch maintains snooping tables for each VLAN. +### Q: Can OVS populate the kernel flow table in advance instead of in reaction to packets? + +A: No. There are several reasons: + + - Kernel flows are not as sophisticated as OpenFlow flows, which + means that some OpenFlow policies could require a large number of + kernel flows. The "conjunctive match" feature is an extreme + example: the number of kernel flows it requires is the product of + the number of flows in each dimension. + + - With multiple OpenFlow flow tables and simple sets of actions, the + number of kernel flows required can be as large as the product of + the number of flows in each dimension. With more sophisticated + actions, the number of kernel flows could be even larger. + + - Open vSwitch is designed so that any version of OVS userspace + interoperates with any version of the OVS kernel module. This + forward and backward compatibility requires that userspace observe + how the kernel module parses received packets. This is only + possible in a straightforward way when userspace adds kernel flows + in reaction to received packets. + + For more relevant information on the architecture of Open vSwitch, + please read "The Design and Implementation of Open vSwitch", + published in USENIX NSDI 2015. + Performance ----------- @@ -1886,6 +1979,25 @@ A: When a switch sends a packet to an OpenFlow controller using a buffering that the OpenFlow specification requires implementations to document. +### Q: How does OVS divide flows among buckets in an OpenFlow "select" group? + +A: In Open vSwitch 2.3 and earlier, Open vSwitch used the destination + Ethernet address to choose a bucket in a select group. + + Open vSwitch 2.4 and later by default hashes the source and + destination Ethernet address, VLAN ID, Ethernet type, IPv4/v6 + source and destination address and protocol, and for TCP and SCTP + only, the source and destination ports. The hash is "symmetric", + meaning that exchanging source and destination addresses does not + change the bucket selection. + + Select groups in Open vSwitch 2.4 and later can be configured to + use a different hash function, using a Netronome extension to the + OpenFlow 1.5+ group_mod message. For more information, see + Documentation/group-selection-method-property.txt in the Open + vSwitch source tree. (OpenFlow 1.5 support in Open vSwitch is still + experimental.) + Development -----------