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TNSR IDS Setup using ERSPAN

Test Layout:

Role IP Address Interface
Traffic source VM 203.0.113.10/24 ens224
TNSR WAN 203.0.113.2/24 GigabitEthernet13/0/0
TNSR LAN 192.0.2.1/24 GigabitEthernet1b/0/0
IDS/Target VM 192.0.2.5/24 ens256

GRE/ERSPAN Layout:

GRE Role Value
GRE/ERSPAN Source 192.0.2.1
GRE/ERSPAN Receiver 192.0.2.5
Interface spanned to GRE GigabitEthernet13/0/0

TNSR Setup

Add the ACL which will be filled by tnsrids, it needs a permit rule that will always come last:

configure
acl snortblock
rule 2147483646
action permit
ip-version ipv4
exit
exit

Configure the external interface, and add the ACL from above:

interface GigabitEthernet13/0/0
ip address 203.0.113.2/24
description External/WAN
access-list input acl snortblock sequence 10
enable
exit

Configure the internal interface:

interface GigabitEthernet1b/0/0
ip address 192.0.2.1/24
description Internal/LAN
enable
exit

Configure the GRE/ERSPAN interface and corresponding SPAN:

gre gre1
dest 192.0.2.5
source 192.0.2.1
tunnel-type erspan session-id 1
instance 1
exit
int gre1
enable
exit
span GigabitEthernet13/0/0
onto gre1 hw both
exit

Enable the RESTCONF server:

restconf
enable true
global authentication-type client-certificate
global server-certificate SRV
global server-key SRV
global server-ca-cert-path TNSR
server dataplane 192.0.2.1 443 true

WARNING: You are able to use previously created certificate or to create it through the TNSR

Setup tnsrids Daemon

See README.md

IDS Receiver Setup

Setup the network interface used between the IDS Receiver and TNSR

$ sudo vi /etc/sysconfig/network-scripts/ifcfg-ens256
TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_FAILURE_FATAL=no
IPV6_ADDR_GEN_MODE=stable-privacy
NAME=ens256
UUID=b2953c4e-5fac-411b-b357-6dd50260062f
DEVICE=ens256
ONBOOT=yes
IPADDR=192.0.2.5
PREFIX=24
#GATEWAY=192.0.2.1
DNS1=192.0.2.1
DOMAIN="example.com"
IPV6_PRIVACY=no

This route is added for testing to/from hosts on the TNSR WAN side:

$ sudo vi /etc/sysconfig/network-scripts/route-ens256
203.0.113.0/24 via 192.0.2.1 dev ens256

Use this command to temporarily add a the route instead of making it permanent:

$ sudo route add -net 203.0.113.0/24 gw 192.0.2.1

Traffic arriving on this system will need to be passed through the host firewall which is likely firewalld if this is a CentOS system. Alternately, disable firewalld since this system should be isolated on the network and only receiving traffic:

$ sudo systemctl stop firewalld
$ sudo systemctl disable firewalld

Restart the network and pick up the new interface configuration::

$ sudo systemctl restart network

This next step is likely optional. There is no need to process or handle the received traffic on an interface in this way, it only needs to arrive at the interface snort is bound to, it can decode the GRE directly.

$ sudo modprobe ip_gre
sudo vi /etc/sysconfig/network-scripts/ifcfg-tun0
DEVICE=tun0
BOOTPROTO=none
ONBOOT=yes
TYPE=GRE
#PEER_INNER_IPADDR=198.18.0.1
PEER_OUTER_IPADDR=192.0.2.1
#MY_INNER_IPADDR=198.18.0.2
MY_OUTER_IPADDR=192.0.2.5

$ sudo ifup tun0

Setup snort, for example on CentOS by following https://upcloud.com/resources/tutorials/installing-snort-on-centos

Snort DOES NOT need to run on the GRE interface/tun, only on the interface with the address used to receive the GRE/ERSPAN traffic. Snort will see and decapsulate the GRE traffic internally.

Snort HOME_NET should include addresses from TNSR to alert on:

ipvar HOME_NET [192.0.2.0/24,203.0.113.2/32]

In the snort configuration, use alert_syslog output:

output alert_syslog: LOG_LOCAL5 LOG_ALERT

Run snort:

$ sudo snort -i ens256 -u snort -g snort -c /etc/snort/snort.conf

Configure rsyslog to transport messages to the host where tnsrids is running::

$ sudo vi /etc/rsyslog.conf
local5.* @172.27.10.36:12345

Restart rsyslog:

$ sudo systemctl restart rsyslog

A rule to flag any ICMP traffic is a good test to generate alerts quickly.

$ sudo vi /etc/snort/rules/local.rules
alert icmp !$HOME_NET any -> $HOME_NET any (msg:"ICMP test"; sid:10000001; rev:001;

Traffic Generator Setup (Testing)

$ sudo vi /etc/sysconfig/network-scripts/ifcfg-ens224
TYPE=Ethernet
PROXY_METHOD=none
BROWSER_ONLY=no
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_FAILURE_FATAL=no
IPV6_ADDR_GEN_MODE=stable-privacy
NAME=ens224
UUID=5a2a73ce-3c7b-4cf0-b32c-309c50247b77
DEVICE=ens224
ONBOOT=yes
IPADDR=203.0.113.10
PREFIX=24
#GATEWAY=172.27.44.1
#DNS1=172.27.32.5
#DNS2=172.27.32.6
DOMAIN="example.com"
IPV6_PRIVACY=no

Add a route similar to the IDS box, to reach the other side:

$ sudo vi /etc/sysconfig/network-scripts/route-ens224
192.0.2.0/24 via 203.0.113.2 dev ens224

Or temporarily add the route:

$ sudo route add -net 192.0.2.0/24 gw 203.0.113.2

Restart the network services to pick up new interface settings::

$ sudo systemctl restart network

When testing, use ping or hping to source traffic from other addresses, to see if alerts trigger ACL entries as expected:

$ ping -I ens224 203.0.113.2
$ sudo hping 203.0.113.2 -I ens224 --icmp --spoof 203.0.113.66
$ nc -vz -s 203.0.113.10 203.0.113.2 22

Install hping from FreeBSD packages/ports or using your distribution's package manager (on CentOS it is hping3, available with epel-release). Similarly, nmap and its included utility nc are useful for generating traffic that can tickle snort to alert.

CentOS 7:

$ sudo yum install epel-release
$ sudo yum install hping3 nmap

Resources

IDS configuration used during testing: snort.conf