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SNF: Synthesizing high performance NFV service chains

A framework to turn a chain of Click-based network functions (NFs) into a synthesized network function (SNF). Our PeerJ Computer Science journal article provides more information about SNF.

If you use SNF in your work, please cite our article:

	author       = {Katsikas, Georgios P. and Enguehard, Marcel and Ku\'{z}niar, Maciej and Maguire Jr., Gerald Q. and Kosti\'{c}, Dejan},
	title        = {{SNF: Synthesizing high performance NFV service chains}},
	journal      = {PeerJ Computer Science},
	volume       = {2},
	pages        = {e98},
	numpages     = {30},
	month        = nov,
	year         = {2016},
	doi          = {10.7717/peerj-cs.98},
	issn         = {2376-5992},
	url          = {},
	publisher    = {PeerJ Inc.},
	keywords     = {NFV, service chains, synthesis, single-read-single-write, line-rate, 40 Gbps},

Moreover, the doctoral thesis of Georgios P. Katsikas presents an even more thorough performance evaluation of SNF in Chapter 7.

I. Basic Installation

SNF is implemented in C++ and uses autotools. To build and run SNF, follow the steps below:

A. Checkout SNF and Build Dependencies

  • git clone
  • cd snf/
  • export SNF_HOME=$(pwd)
  • ./build_deps

B. Download and Configure Click

Note that currently, the build process assumes that your Click binaries reside in the default location /usr/local/. In case you want to use the DPDK I/O, compile DPDK 19.02. Earlier versions are also tested and work well. Moreover, SNF can be configured to generate synthesized service chains based on FastClick; a faster variant of the Click modular router. More information about SNF's configuration is provided in Section II.

  • git clone

  • cd ./click

  • export CLICK_HOME=$(pwd)

  • git checkout snf

    • Normal Click (User-space):

      ./configure --enable-user-multithread --enable-multithread \ --enable-intel-cpu --enable-nanotimestamp \ --enable-all-elements

    • Click-Netmap (User-space, after building Netmap):

      ./configure --with-netmap=${NETMAP_DIR}/sys --enable-multithread \ --disable-linuxmodule --enable-intel-cpu \ --enable-user-multithread --verbose --enable-select=poll \ CFLAGS="-O3" CXXFLAGS="-std=gnu++11 -O3" \ --disable-dynamic-linking --enable-poll \ --enable-bound-port-transfer --enable-nanotimestamp \ --enable-all-elements

    • Click-DPDK (User-space, after building DPDK):

      ./configure RTE_SDK=${DPDK_DIR} RTE_TARGET=x86_64-native-linuxapp-gcc \ --verbose CFLAGS="-std=gnu11 -g -O3" \ CXXFLAGS="-g -std=gnu++14 -O3" \ --disable-linuxmodule \ --enable-intel-cpu --enable-multithread \ --enable-user-multithread --disable-dynamic-linking \ --enable-poll --enable-bound-port-transfer \ --enable-dpdk --with-netmap=no \ --enable-nanotimestamp --enable-json --enable-all-elements

  • make -j 8

  • sudo make install (uses default prefix=/usr/local/)

C. Build SNF

  • cd ${SNF_HOME}
  • Build SNF according to INSTALL
  • Create an input property file of your wished service chain, following the example in: input/tests/tests.prop
    • Make sure that the Click configurations you specify in the property file are valid paths.
  • SNF can be instructed (via the property file) to generate either a Click or a FastClick synthesized service chain. This allows to reap the benefits of FastClick's advanced thread scheduling, computational batching, and fast user-space I/O, while maintaining compatibility with Click.

D. Run SNF

To synthesize and deploy your service chain do:

  • ./ <snf-exec> <your property file> will load the property file and generate the synthesized chain in the specified folder.
  • To run a Click-based SNF: click <>
  • To run a (Fast)Click-based SNF with DPDK: click --dpdk -c 0xffff -v -- <>

II. Multi-core SNF

There are various ways to deploy SNF across multiple cores. We currently support Click-DPDK and FastClick with DPDK, both using Receive-Side Scaling (RSS) as follows:

  • Build SNF with DPDK support following the steps above.
  • Input a set of Click-based NFs, even if they do not use DPDK-based I/O. SNF will output DPDK-based I/O instructions if configured with DPDK.
  • In the [GENERIC] section of the input property file set:
    • NUMA = true/false
    • CPU_SOCKETS = (M is the number of the target machine's sockets)
    • CPU_CORES = (N is the total number of CPU cores on this machine)
    • NIC_HW_QUEUES = (K is the number of hardware queues in your NIC. Indicatively, this number should be adjusted to the number of available CPU cores above)
  • Run SNF and check the folder OUTPUT_FOLDER for a file as specified in the property file.
  • You will see a synthesized service chain, replicated across all the requested queues. Each queue has a dedicated thread that is statically assigned to a CPU core, hence your SNF service chain can read packets from all of these queues and execute the service chain's pipeline in parallel.
  • Underneath this system, the DPDK I/O uses RSS to hash incoming packets to different hardware queues. See the RSS sections below.

A. Receive-Side Scaling (RSS)

Click-DPDK or FastClick use RSS by default. The default hash function is specified in the lib/ file using struct rte_eth_conf. This data structure contains a member structure struct rte_eth_rxmode rxmode which in turn contains a field mq_mode (multi-queue mode in the receiver) that is set to ETH_MQ_RX_RSS (RSS in on). The RSS configuration can be adjusted by modifying rx_adv_conf.rss_conf.rss_key (NULL by default) and rx_adv_conf.rss_conf.rss_hf (ETH_RSS_IP by default). This configuration means that the IP address field is used in the hash function to split the packets. To explore other possibilities in DPDK, refer to ${DPDK_DIR}/lib/librte_ether/rte_ethdev.h and search for keyword ETH_RSS_. An important property we might want to explore is how to run RSS in symmetric mode.

B. Symmetric RSS

Many networking applications operate on a per-flow basis and you don't want this information being shared among different CPUs. Therefore, it is very important to have the same CPU handling both sides of a connection (bi-directional or symmetrical flows). A group of researchers found that there is a specific hash key which offers this property for TCP flows. You can read more details in their paper. The hash key (in case you don't want to read the paper) is:

static uint8_t symmetric_hashkey[40] = {

0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A,

0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A, 0x6D, 0x5A


Go to int DPDKDevice::initialize_device in lib/ and replace:

dev_conf.rx_adv_conf.rss_conf.rss_key = NULL;


dev_conf.rx_adv_conf.rss_conf.rss_key = symmetric_hashkey;

Our snf branch in Click takes care of this.

III. SNF as part of Metron (USENIX NSDI 2018)

SNF is used by Metron to realize NFV service chains at the true speed of the underlying hardware. For more information read our USENIX NSDI 2018 paper and watch my talk at NSDI.

	author       = {Katsikas, Georgios P. and Barbette, Tom and Kosti\'{c}, Dejan and Steinert, Rebecca and Maguire Jr., Gerald Q.},
	title        = {{Metron: NFV Service Chains at the True Speed of the Underlying Hardware}},
	booktitle    = {15th USENIX Conference on Networked Systems Design and Implementation (NSDI 18)},
	series       = {NSDI'18},
	year         = {2018},
	isbn         = {978-1-931971-43-0},
	pages        = {171--186},
	numpages     = {16},
	url          = {},
	address      = {Renton, WA},
	publisher    = {{USENIX} Association}

Additional information about Metron can be found in my doctoral thesis.

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