DDoS Protection

FastNetMon

FastNetMon is a high-performance DDoS detector/sensor built on top of multiple packet capture engines: NetFlow, IPFIX, sFlow, AF_PACKET (port mirror). It can detect hosts in the deployed network sending or receiving large volumes of traffic, packets/bytes/flows per second and perform a configurable action to handle that event, such as calling a custom script.

VyOS includes the FastNetMon Community Edition.

Configuration

set service ids ddos-protection alert-script <text>

Configure alert script that will be executed when an attack is detected.

set service ids ddos-protection ban-time <1-4294967294>

Configure how long an IP (attacker) should be kept in blocked state. Default value is 1900.

set service ids ddos-protection direction [in | out]

Configure direction for processing traffic.

set service ids ddos-protection exclude-network <x.x.x.x/x>
set service ids ddos-protection exclude-network <h:h:h:h:h:h:h:h/x>

Specify IPv4 and/or IPv6 networks which are going to be excluded.

set service ids ddos-protection listen-interface <text>

Configure listen interface for mirroring traffic.

set service ids ddos-protection mode [mirror | sflow]

Configure traffic capture mode.

set service ids ddos-protection network <x.x.x.x/x>
set service ids ddos-protection network <h:h:h:h:h:h:h:h/x>

Specify IPv4 and/or IPv6 networks that should be protected/monitored.

set service ids ddos-protection sflow listen-address <x.x.x.x>

Configure local IPv4 address to listen for sflow.

set service ids ddos-protection sflow port <1-65535>

Configure port number to be used for sflow connection. Default port is 6343.

set service ids ddos-protection threshold general [fps | mbps | pps] <0-4294967294>

Configure general threshold parameters.

set service ids ddos-protection threshold icmp [fps | mbps | pps] <0-4294967294>

Configure ICMP threshold parameters.

set service ids ddos-protection threshold tcp [fps | mbps | pps] <0-4294967294>

Configure TCP threshold parameters

set service ids ddos-protection threshold udp [fps | mbps | pps] <0-4294967294>

Configure UDP threshold parameters

Example

A configuration example can be found in this section. In this simplified scenario, main things to be considered are:

  • Network to be protected: 192.0.2.0/24 (public IPs use by customers)

  • ban-time and threshold: these values are kept very low in order to easily identify and generate and attack.

  • Direction: in and out. Protect public network from external attacks, and identify internal attacks towards internet.

  • Interface eth0 used to connect to upstream.

Since we are analyzing attacks to and from our internal network, two types of attacks can be identified, and different actions are needed:

  • External attack: an attack from the internet towards an internal IP is identify. In this case, all connections towards such IP will be blocked

  • Internal attack: an attack from the internal network (generated by a customer) towards the internet is identify. In this case, all connections from this particular IP/Customer will be blocked.

So, firewall configuration needed for this setup:

set firewall group address-group FNMS-DST-Block
set firewall group address-group FNMS-SRC-Block

set firewall ipv4 forward filter rule 10 action 'drop'
set firewall ipv4 forward filter rule 10 description 'FNMS - block destination'
set firewall ipv4 forward filter rule 10 destination group address-group 'FNMS-DST-Block'

set firewall ipv4 forward filter rule 20 action 'drop'
set firewall ipv4 forward filter rule 20 description 'FNMS - Block source'
set firewall ipv4 forward filter rule 20 source group address-group 'FNMS-SRC-Block'

Then, FastNetMon configuration:

set service ids ddos-protection alert-script '/config/scripts/fnm-alert.sh'
set service ids ddos-protection ban-time '10'
set service ids ddos-protection direction 'in'
set service ids ddos-protection direction 'out'
set service ids ddos-protection listen-interface 'eth0'
set service ids ddos-protection mode 'mirror'
set service ids ddos-protection network '192.0.2.0/24'
set service ids ddos-protection threshold general pps '100'

And content of the script:

#!/bin/bash

# alert-script is called twice.
# When an attack occurs, the program calls a bash script twice:
# 1st time when threshold exceed
# 2nd when we collect 100 packets for detailed audit of what happened.

# Do nothing if “attack_details” is passed as an argument
if [ "${4}" == "attack_details" ]; then
    # Do nothing
    exit
fi
# Arguments:
ip=$1
direction=$2
pps_rate=$3
action=$4

logger -t FNMS "** Start - Running alert script **"

if [ "${direction}" == "incoming" ] ; then
    group="FNMS-DST-Block"
    origin="external"
else
    group="FNMS-SRC-Block"
    origin="internal"
fi

if [ "${action}" == "ban" ] ; then
    logger -t FNMS "Attack detected for IP ${ip} and ${direction} direction from ${origin} network. Need to block IP address."
    logger -t FNMS "Adding IP address ${ip} to firewall group ${group}."
    sudo nft add element ip vyos_filter A_${group} { ${ip} }
else
    logger -t FNMS "Timeout for IP ${ip}, removing it from group ${group}."
    sudo nft delete element ip vyos_filter A_${group} { ${ip} }
fi
logger -t FNMS "** End - Running alert script **"
exit