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+---
+title: "FD.io CSIT Logical Topologies"
+weight: 4
+---
+
+# FD.io CSIT Logical Topologies
+
+CSIT VPP performance tests are executed on physical testbeds. Based on the
+packet path thru server SUTs, three distinct logical topology types are used
+for VPP DUT data plane testing:
+
+1. NIC-to-NIC switching topologies.
+2. VM service switching topologies.
+3. Container service switching topologies.
+
+## NIC-to-NIC Switching
+
+The simplest logical topology for software data plane application like
+VPP is NIC-to-NIC switching. Tested topologies for 2-Node and 3-Node
+testbeds are shown in figures below.
+
+{{< figure src="/cdocs/logical-2n-nic2nic.svg" >}}
+
+{{< figure src="/cdocs/logical-3n-nic2nic.svg" >}}
+
+Server Systems Under Test (SUT) run VPP application in Linux user-mode
+as a Device Under Test (DUT). Server Traffic Generator (TG) runs T-Rex
+application. Physical connectivity between SUTs and TG is provided using
+different drivers and NIC models that need to be tested for performance
+(packet/bandwidth throughput and latency).
+
+From SUT and DUT perspectives, all performance tests involve forwarding
+packets between two (or more) physical Ethernet ports (10GE, 25GE, 40GE,
+100GE). In most cases both physical ports on SUT are located on the same
+NIC. The only exceptions are link bonding and 100GE tests. In the latter
+case only one port per NIC can be driven at linerate due to PCIe Gen3
+x16 slot bandwidth limiations. 100GE NICs are not supported in PCIe Gen3
+x8 slots.
+
+Note that reported VPP DUT performance results are specific to the SUTs
+tested. SUTs with other processors than the ones used in FD.io lab are
+likely to yield different results. A good rule of thumb, that can be
+applied to estimate VPP packet thoughput for NIC-to-NIC switching
+topology, is to expect the forwarding performance to be proportional to
+processor core frequency for the same processor architecture, assuming
+processor is the only limiting factor and all other SUT parameters are
+equivalent to FD.io CSIT environment.
+
+## VM Service Switching
+
+VM service switching topology test cases require VPP DUT to communicate
+with Virtual Machines (VMs) over vhost-user virtual interfaces.
+
+Two types of VM service topologies are tested:
+
+1. "Parallel" topology with packets flowing within SUT from NIC(s) via
+   VPP DUT to VM, back to VPP DUT, then out thru NIC(s).
+2. "Chained" topology (a.k.a. "Snake") with packets flowing within SUT
+   from NIC(s) via VPP DUT to VM, back to VPP DUT, then to the next VM,
+   back to VPP DUT and so on and so forth until the last VM in a chain,
+   then back to VPP DUT and out thru NIC(s).
+
+For each of the above topologies, VPP DUT is tested in a range of L2
+or IPv4/IPv6 configurations depending on the test suite. Sample VPP DUT
+"Chained" VM service topologies for 2-Node and 3-Node testbeds with each
+SUT running N of VM instances is shown in the figures below.
+
+{{< figure src="/cdocs/logical-2n-vm-vhost.svg" >}}
+
+{{< figure src="/cdocs/logical-3n-vm-vhost.svg" >}}
+
+In "Chained" VM topologies, packets are switched by VPP DUT multiple
+times: twice for a single VM, three times for two VMs, N+1 times for N
+VMs. Hence the external throughput rates measured by TG and listed in
+this report must be multiplied by N+1 to represent the actual VPP DUT
+aggregate packet forwarding rate.
+
+For "Parallel" service topology packets are always switched twice by VPP
+DUT per service chain.
+
+Note that reported VPP DUT performance results are specific to the SUTs
+tested. SUTs with other processor than the ones used in FD.io lab are
+likely to yield different results. Similarly to NIC-to-NIC switching
+topology, here one can also expect the forwarding performance to be
+proportional to processor core frequency for the same processor
+architecture, assuming processor is the only limiting factor. However
+due to much higher dependency on intensive memory operations in VM
+service chained topologies and sensitivity to Linux scheduler settings
+and behaviour, this estimation may not always yield good enough
+accuracy.
+
+## Container Service Switching
+
+Container service switching topology test cases require VPP DUT to
+communicate with Containers (Ctrs) over memif virtual interfaces.
+
+Three types of VM service topologies are tested in |csit-release|:
+
+1. "Parallel" topology with packets flowing within SUT from NIC(s) via
+   VPP DUT to Container, back to VPP DUT, then out thru NIC(s).
+2. "Chained" topology (a.k.a. "Snake") with packets flowing within SUT
+   from NIC(s) via VPP DUT to Container, back to VPP DUT, then to the
+   next Container, back to VPP DUT and so on and so forth until the
+   last Container in a chain, then back to VPP DUT and out thru NIC(s).
+3. "Horizontal" topology with packets flowing within SUT from NIC(s) via
+   VPP DUT to Container, then via "horizontal" memif to the next
+   Container, and so on and so forth until the last Container, then
+   back to VPP DUT and out thru NIC(s).
+
+For each of the above topologies, VPP DUT is tested in a range of L2
+or IPv4/IPv6 configurations depending on the test suite. Sample VPP DUT
+"Chained" Container service topologies for 2-Node and 3-Node testbeds
+with each SUT running N of Container instances is shown in the figures
+below.
+
+{{< figure src="/cdocs/logical-2n-container-memif.svg" >}}
+
+{{< figure src="/cdocs/logical-3n-container-memif.svg" >}}
+
+In "Chained" Container topologies, packets are switched by VPP DUT
+multiple times: twice for a single Container, three times for two
+Containers, N+1 times for N Containers. Hence the external throughput
+rates measured by TG and listed in this report must be multiplied by N+1
+to represent the actual VPP DUT aggregate packet forwarding rate.
+
+For a "Parallel" and "Horizontal" service topologies packets are always
+switched by VPP DUT twice per service chain.
+
+Note that reported VPP DUT performance results are specific to the SUTs
+tested. SUTs with other processor than the ones used in FD.io lab are
+likely to yield different results. Similarly to NIC-to-NIC switching
+topology, here one can also expect the forwarding performance to be
+proportional to processor core frequency for the same processor
+architecture, assuming processor is the only limiting factor. However
+due to much higher dependency on intensive memory operations in
+Container service chained topologies and sensitivity to Linux scheduler
+settings and behaviour, this estimation may not always yield good enough
+accuracy.