Introduction

Since the beginning of July 2012, OISF team is able to access to a server where one interface is receivingsome mirrored real European traffic. When reading "some", think between 5Gbps and 9.5Gbpsconstant traffic. With that traffic, this is around 1Mpps to
1.5M packet per seconds we have to study.

The box itself is a standard server with the following characteristics:

• CPU: One Intel(R) Xeon(R) CPU E5-2680 0 @ 2.70GHz (16 cores counting Hyperthreading)
• Memory: 32Go
• capture NIC: Intel 82599EB 10-Gigabit SFI/SFP+

The objective is simple: be able to run Suricata on this box and treat the wholetraffic with a decent number of rules. With the constraint not to use any nonofficial system code (plain system and kernel if we omit a driver).

The code on the box have been updated October 4th:

• It runs Suricata 1.4beta2
• with 6719 signatures
• and 0% packet loss
• with setup described below

The setup is explained by the following schema:We
want to use the multiqueue system on the Intel card to be able to load balance the treatment. Next goal is to have one single CPU to treat the packet from the start to the end.

Peter Manev, Matt Jonkmann, Anoop Saldanha and Eric Leblond (myself) have been involved inthe here described setup.

Detailed method

The Intel NIC benefits from a multiqueue system. The RX/TX traffic can be load-balancedon different interrupts. In our case, this permit to handle a part of the flow on eachCPU. One really interesting thing is that the load-balancing can be done with respectto
the IP flows. By default, one RX queue is created per-CPU.

More information about multiqueue ethernet devices can be found in the documentnetworking/scaling.txt in the Documentation directory of Linux
sources.

Suricata is able to do zero-copy in AF_PACKET capture mode. One other interesting featureof this mode is that you can have multiple threads listening to the same interface. Inour case, we can start one threads per queue to have a load-balancing of capture
on allour resources.

Suricata has different running modes which define how the different parts of the engine(decoding, streaming, siganture, output) are chained. One of the mode is the ‘workers’mode where all the treatment for a packet is made on a single thread. This mode isadapted
to our setup as it will permit to keep the work from start to end on a singlethread. By using the CPU affinity system available in Suricata, we can assign eachthread to a single CPU. By doing this the treatment of each packet can be done ona single CPU.

But this does not solve one problem which is the link between the CPU receiving the packetand the one used in Suricata.To do so we have to ensure that when a packet is received on a queue, the CPU that willhandle the packet will be the same as the one treating
the packet in Suricata. DavidMiller had already planned this kind of setup when coding the fanout mode of AF_PACKET.One of the flow load balancing mode is flow_cpu. In this mode, the packet is delivered tothe same track depending on the CPU.

The dispatch is made by using the formula "cpu % num" where cpu is the cpu number andnum is the number of socket bound to the same fanout socket. By the way, this implyyou can’t have a number of sockets superior to the number of CPUs.A code study shows that
the assignement in the array of sockets is incrementally made.Thus first socket to bind will be assigned to the first CPU, etc..In case, a socket disconnect from the set, the last socket of the array will take the empty place.This implies the optimizations
will be partially lost in case of a disconnect.

By using the flow_cpu dispatch of AF_PACKET and the workers mode of Suricata, we canmanage to keep all work on the same CPU.

Preparing the system

The operating system running on is an Ubuntu 12.04 and the driver igxbewas outdated.Using the instruction available on Intel website (README.txt),we’ve updated the driver.Next
step was to unload the old driver and load the new one

sudo rmmod ixgbe

sudo modprobe ixgbe FdirPballoc=3

Doing this we’ve also tried to use the RSS variable. But it seems there is an issue, as we still having 16 queues although the RSS params wasset to 8.

Once done, the next thing is to setup the IRQ handling to have each CPU linked in order withthe corresponding RX queue. irqbalance was running on the system and the setup wascorrectly made.

The interface was using IRQ 101 to 116 and /proc/interrupts show a diagonale indicatingthat each CPU was assigned to one interrupt.

If not, it was possible to use the instruction contained in IRQ-affinity.txt availablein the Documentation directory of Linux sources.

But the easy way to do it is to use the script provided with the driver:

ixgbe-3.10.16/scripts$ ./set_irq_affinity.sh eth3

Note: Intel latest driver was responsible of a decrease of CPU usage. With Ubuntu kernel version, the CPU usage as 80% and it is 45% with latest Intel driver.

The card used on the system was not load-balancing UDP flow using port. We had to use‘ethtool’ to fix this

regit@suricata:~$ sudo ethtool -n eth3 rx-flow-hash udp4

UDP over IPV4 flows use these fields for computing Hash flow key:

IP SA

IP DA

regit@suricata:~$ sudo ethtool -N eth3 rx-flow-hash udp4 sdfn

regit@suricata:~$ sudo ethtool -n eth3 rx-flow-hash udp4

UDP over IPV4 flows use these fields for computing Hash flow key:

IP SA

IP DA

L4 bytes 0 & 1 [TCP/UDP src port]

L4 bytes 2 & 3 [TCP/UDP dst port]

In our case, the default setting of the ring parameters of the card, seemsto indicate it is possible to increase the ring buffer on the card

regit@suricata:~$ ethtool -g eth3

Ring parameters for eth3:

Pre-set maximums:

RX:             4096

RX Mini:        0

RX Jumbo:       0

TX:             4096

Current hardware settings:

RX:             512

RX Mini:        0

RX Jumbo:       0

TX:             512

Our system is now ready and we can start configuring Suricata.

Suricata setup

Global variables

The run mode has been set to ‘workers’

max-pending-packets: 512

runmode: workers

As pointed out by Victor Julien, this is not necessary to increase max-pending-packets too much because only a number of packets equal to the total number of worker threads can be treated simultaneously.

Suricata 1.4beta1 introduce a delayed-detect variable under detect-engine. If set to yes, this trigger a build of signature after the packet capture threads have started working. This is a potential issue if your system is short in CPU
as the task of building the detect engine is CPU intensive and can cause some packet loss. That’s why it is recommended to let it to the default value of
no.

AF_PACKET

The AF_PACKET configuration is almost straight forward

af-packet:

  - interface: eth3

    threads: 16

    cluster-id: 99

    cluster-type: cluster_cpu

    defrag: yes

    use-mmap: yes

    ring-size: 300000

Affinity

Affinity settings permit to assign thread to set of CPUs. In our case, we onlSet to have in exclusive mode one packet thread dedicated to each CPU. The settingused to define packet thread property in ‘workers’ mode is ‘detect-cpu-set’

threading:

  set-cpu-affinity: yes

  cpu-affinity:

    - management-cpu-set:

      cpu: [ "all" ]

      mode: "balanced"

      prio:

        default: "low"

  - detect-cpu-set:

      cpu: ["all"]

      mode: "exclusive" # run detect threads in these cpus

      prio:

        default: "high"

The idea is to assign the highest prio to detect threads and to let the OS do its bestto dispatch the remaining work among the CPUs (balanced mode on all CPUs for the management).

Defrag

Some tuning was needed here. The network was exhibing some serious fragmentationand we have to modify the default settings

defrag:

  memcap: 512mb

  trackers: 65535 # number of defragmented flows to follow

  max-frags: 65535  # number of fragments

The ‘trackers’ variable was not documented in the original YAML configuration file.Although defined in the YAML, the ‘max-frags’ one was not used by Suricata. A patchhas been made to implement this.

Streaming

The variables relative to streaming have been set very high

stream:

  memcap: 12gb

  max-sessions: 20000000

  prealloc-sessions: 10000000

  inline: no                    # no inline mode

  reassembly:

    memcap: 14gb

    depth: 6mb                  # reassemble 1mb into a stream

    toserver-chunk-size: 2560

    toclient-chunk-size: 2560

To detect the potential issue with memcap, one can read the ‘stats.log’ filewhich contains various counters. Some of them matching the ‘memcap’ string.

Running suricata

Suricata can now be runned with the usual command line

sudo suricata -c /etc/suricata.yaml --af-packet=eth3

Our affinity setup is working as planned as show the following log line

Setting prio -2 for "AFPacketeth34" Module to cpu/core 3, thread id 30415

Tests

Tests have been made by simply running Suricata against the massive trafficmirrored on the eth3 interface.

At first, we started Suricata without rules to see if it was able to dealwith the amount of packets for a long period. Most of the tuning was doneduring this phase.

To detect packet loss, the capture keyword can be search in ‘stats.log’.If ‘kernel_drops’ is set to 0, this is good

capture.kernel_packets    | AFPacketeth315            | 1436331302

capture.kernel_drops      | AFPacketeth315            | 0

capture.kernel_packets    | AFPacketeth316            | 1449320230

capture.kernel_drops      | AFPacketeth316            | 0

The statistics are available for each thread. For example, ‘AFPacketeth315′ isthe 15th AFPacket thread bound to eth3.

When this phase was complete we did add some rules by using Emerging Threat PRO rulesfor malware, * and some others:

rule-files:

 - *.rules

 - malware.rules

 - chat.rules

 - current_events.rules

 - dns.rules

 - mobile_malware.rules

 - scan.rules

 - user_agents.rules

 - web_server.rules

 - worm.rules

This ruleset has the following characterics:

• 6719 signatures processed
• 8 are IP-only rules
• 2307 are inspecting packet payload
• 5295 inspect application layer
• 0 are decoder event only

This is thus a decent ruleset with a high part of application level event which require acomplex processing. With that ruleset, there is more than 16 alerts per second (output in unified2 format).

With the previously mentioned ruleset, the load of each CPU is around 60% and Suricatais remaining stable during hours long run.

In most run, we’ve observed some packet loss between capture start and first time Suricata grab the statistics. It seems the initialization phase is not fast enough.

Conclusion

OISF team has access to the box for a week now and has alreadymanaged to get real performance. We will continue to work on it to providethe best possible experience to all Suricata’s users.

Feel free to made any remark and suggestion about this blog post and this setup.