Setting up IPS/inline for Linux ================================ Setting up IPS with Netfilter ----------------------------- In this guide will be explained how to work with Suricata in layer3 inline mode and how to set iptables for that purpose. First start with compiling Suricata with NFQ support. For instructions see `Ubuntu Installation `_. For more information about NFQ and iptables, see :ref:`suricata-yaml-nfq`. To check if you have NFQ enabled in your Suricata, enter the following command: :: suricata --build-info and examine if you have NFQ between the features. To run suricata with the NFQ mode, you have to make use of the -q option. This option tells Suricata which of the queue numbers it should use. :: sudo suricata -c /etc/suricata/suricata.yaml -q 0 Iptables configuration ~~~~~~~~~~~~~~~~~~~~~~ First of all it is important to know which traffic you would like to send to Suricata. Traffic that passes your computer or traffic that is generated by your computer. .. image:: setting-up-ipsinline-for-linux/IPtables.png .. image:: setting-up-ipsinline-for-linux/iptables1.png If Suricata is running on a gateway and is meant to protect the computers behind that gateway you are dealing with the first scenario: *forward_ing* . If Suricata has to protect the computer it is running on, you are dealing with the second scenario: *host* (see drawing 2). These two ways of using Suricata can also be combined. The easiest rule in case of the gateway-scenario to send traffic to Suricata is: :: sudo iptables -I FORWARD -j NFQUEUE In this case, all forwarded traffic goes to Suricata. In case of the host situation, these are the two most simple iptables rules; :: sudo iptables -I INPUT -j NFQUEUE sudo iptables -I OUTPUT -j NFQUEUE It is possible to set a queue number. If you do not, the queue number will be 0 by default. Imagine you want Suricata to check for example just TCP-traffic, or all incoming traffic on port 80, or all traffic on destination-port 80, you can do so like this: :: sudo iptables -I INPUT -p tcp -j NFQUEUE sudo iptables -I OUTPUT -p tcp -j NFQUEUE In this case, Suricata checks just TCP traffic. :: sudo iptables -I INPUT -p tcp --sport 80 -j NFQUEUE sudo iptables -I OUTPUT -p tcp --dport 80 -j NFQUEUE In this example, Suricata checks all input and output on port 80. .. image:: setting-up-ipsinline-for-linux/iptables2.png .. image:: setting-up-ipsinline-for-linux/IPtables3.png To see if you have set your iptables rules correct make sure Suricata is running and enter: :: sudo iptables -vnL In the example you can see if packets are being logged. .. image:: setting-up-ipsinline-for-linux/iptables_vnL.png This description of the use of iptables is the way to use it with IPv4. To use it with IPv6 all previous mentioned commands have to start with 'ip6tables'. It is also possible to let Suricata check both kinds of traffic. There is also a way to use iptables with multiple networks (and interface cards). Example: .. image:: setting-up-ipsinline-for-linux/iptables4.png :: sudo iptables -I FORWARD -i eth0 -o eth1 -j NFQUEUE sudo iptables -I FORWARD -i eth1 -o eth0 -j NFQUEUE The options -i (input) -o (output) can be combined with all previous mentioned options. If you would stop Suricata and use internet, the traffic will not come through. To make internet work correctly, you have to erase all iptables rules. To erase all iptables rules, enter: :: sudo iptables -F Nftables configuration ~~~~~~~~~~~~~~~~~~~~~~ NFtables configuration is straight forward and allows mixing firewall rules with IPS. The concept is to create a dedicated chain for the IPS that will be evaluated after the firewalling rule. If your main table is named `filter` it can be created like so :: nft> add chain filter IPS { type filter hook forward priority 10;} To send all forwarded packets to Suricata one can use :: nft> add rule filter IPS queue To only do it for packets exchanged between eth0 and eth1 :: nft> add rule filter IPS iif eth0 oif eth1 queue nft> add rule filter IPS iif eth1 oif eth0 queue NFQUEUE advanced options ~~~~~~~~~~~~~~~~~~~~~~~~ NFQUEUE mechanism supports some interesting options. The nftables configuration will be shown there but the features are also available in iptables. The full syntax of the queuing mechanism looks as follow :: nft add rule filter IPS queue num 3-5 options fanout,bypass This rule sends matching packets to 3 load-balanced queues starting at 3 and ending at 5. To get the packets in Suricata with this setup, you need to specify multiple queues on command line: :: suricata -q 3 -q 4 -q 5 `fanout` and `bypass` are the two available options: - `fanout`: When used together with load balancing, this will use the CPU ID instead of connection hash as an index to map packets to the queues. The idea is that you can improve performance if there’s a queue per CPU. This requires total with a number of queues superior to 1 to be specified. - `bypass`: By default, if no userspace program is listening on an Netfilter queue, then all packets that are to be queued are dropped. When this option is used, the queue rule behaves like ACCEPT if there is no program listening, and the packet will move on to the next table. The `bypass` option can be used to avoid downtime of link when Suricata is not running but this also means that the blocking feature will not be present. Settings up IPS at Layer 2 -------------------------- AF_PACKET IPS mode ~~~~~~~~~~~~~~~~~~ AF_PACKET capture method is supporting a IPS/Tap mode. In this mode, you just need the interfaces to be up. Suricata will take care of copying the packets from one interface to the other. No iptables or nftables configuration is necessary. You need to dedicate two network interfaces for this mode. The configuration is made via configuration variable available in the description of an AF_PACKET interface. For example, the following configuration will create a Suricata acting as IPS between interface eth0 and eth1: :: af-packet: - interface: eth0 threads: 1 defrag: no cluster-type: cluster_flow cluster-id: 98 copy-mode: ips copy-iface: eth1 buffer-size: 64535 use-mmap: yes - interface: eth1 threads: 1 cluster-id: 97 defrag: no cluster-type: cluster_flow copy-mode: ips copy-iface: eth0 buffer-size: 64535 use-mmap: yes Basically, we’ve got an af-packet configuration with two interfaces. Interface eth0 will copy all received packets to eth1 because of the copy-* configuration variable :: copy-mode: ips copy-iface: eth1 The configuration on eth1 is symmetric :: copy-mode: ips copy-iface: eth0 There is some important points to consider when setting up this mode: - The implementation of this mode is dependent of the zero copy mode of AF_PACKET. Thus you need to set `use-mmap` to yes on both interface. - MTU on both interfaces have to be equal: the copy from one interface to the other is direct and packet bigger then the MTU will be dropped by kernel. - Set different values of cluster-id on both interfaces to avoid conflict. - Any network card offloading creating bigger then physical layer datagram (like GRO, LRO, TSO) will result in packets drop as transmit path can not handle them. - Set `stream.inline` to `auto` or `yes` so Suricata really switches to blocking mode. The `copy-mode` variable can take the following values: - `ips`: the drop keyword is honored and matching packets are dropped. - `tap`: no drop occurs, Suricata acts as a bridge Some specific care must be taken to scale the capture method on multiple threads. As we can't use defrag that will generate too big frames, the in kernel load balancing will not be correct: the IP-only fragment will not reach the same thread as the full featured packet of the same flow because the port information will not be present. A solution is to use eBPF load balancing to get an IP pair load balancing that will be fragmentation resistant. The AF_PACKET IPS Configuration using multiple threads and eBPF load balancing looks like the following: :: af-packet: - interface: eth0 threads: 16 defrag: no cluster-type: cluster_ebpf ebpf-lb-file: /usr/libexec/suricata/ebpf/lb.bpf cluster-id: 98 copy-mode: ips copy-iface: eth1 buffer-size: 64535 use-mmap: yes - interface: eth1 threads: 16 cluster-id: 97 defrag: no cluster-type: cluster_ebpf ebpf-lb-file: /usr/libexec/suricata/ebpf/lb.bpf copy-mode: ips copy-iface: eth0 buffer-size: 64535 use-mmap: yes The eBPF file `/usr/libexec/suricata/ebpf/lb.bpf` may not be present on disk. See :ref:`ebpf-xdp` for more information.