How to Prevent IP Spoofing

To prevent the system from forwarding packets to another interface without trying to decrypt them, the system needs to check for IP spoofing. One method of prevention is to set the IP strict destination multihoming parameter by using the ndd command. When this parameter is set in an SMF manifest, the parameter is set when the system reboots.

Perform the steps in this procedure on both systems.

1. On the system console, assume the Primary Administrator role or become superuser.

   The Primary Administrator role includes the Primary Administrator profile. To create the role and assign the role to a user, see Chapter 2, Working With the Solaris Management Console (Tasks), in System Administration Guide: Basic Administration.

2. Create the site-specific SMF manifest to check for IP spoofing.

   Use the following sample script, /var/svc/manifest/site/spoof_check.xml.

   <?xml version="1.0"?>
   <!DOCTYPE service_bundle SYSTEM "/usr/share/lib/xml/dtd/service_bundle.dtd.1">
   
   <service_bundle type='manifest' name='Custom:ip_spoof_checking'>
   
   <!--    This is a custom smf(5) manifest for this system. Place this
           file in /var/svc/manifest/site, the directory for local
           system customizations. The exec method uses an unstable
           interface to provide a degree of protection against IP
           spoofing attacks when this system is acting as a router.
   
           IP spoof protection can also be achieved by using ipfilter(5).
           If ipfilter is configured, this service can be disabled.
   
           Note: Unstable interfaces might be removed in later
           releases.  See attributes(5).
   -->
   
   <service
           name='site/ip_spoofcheck'
           type='service'
           version='1'>
   
           <create_default_instance enabled='false' />
           <single_instance />
   
           <!--    Don't enable spoof protection until the
                   network is up.
           -->
           <dependency
                   name='basic_network'
                   grouping='require_all'
                   restart_on='none'
                   type='service'>
           <service_fmri value='svc:/milestone/network' />
           </dependency>
   
           <exec_method
                   type='method'
                   name='start'
                   exec='/usr/sbin/ndd -set /dev/ip ip_strict_dst_multihoming 1'
   <!--    
        For an IPv6 network, use the IPv6 version of this command, as in:
                   exec='/usr/sbin/ndd -set /dev/ip ip6_strict_dst_multihoming 1
   -->
                   timeout_seconds='60'
           />
   
           <exec_method
                   type='method'
                   name='stop'
                   exec=':true'
                   timeout_seconds='3'
           />
   
           <property_group name='startd' type='framework'>
                   <propval
                           name='duration'
                           type='astring'
                           value='transient'
                   />
           </property_group>
   
           <stability value='Unstable' />
   
   </service>
   </service_bundle>

3. Import this manifest into the SMF repository.

   # svccfg import /var/svc/manifest/site/spoof_check.xml

4. Enable the ip_spoofcheck service.

   Use the name that is defined in the manifest, /site/ip_spoofcheck.

   # svcadm enable /site/ip_spoofcheck

5. Verify that the ip_spoofcheck service is online.

   # svcs /site/ip_spoofcheck