При сборке пакета xorp выдаётся такое предупреждение:

WARNING: Netfilter include files are broken or do not exist.
  This means the Linux firewall support will not be compiled in.
  To fix, you may edit: /usr/include/linux/netfilter_ipv4/ip_tables.h
  line 222 or so, to look like this:
  /* Helper functions */
  static __inline__ struct ipt_entry_target *
  ipt_get_target(struct ipt_entry *e)
{
        /* BEN:  Was void* */
        return (struct ipt_entry_target *)((char*)e + e->target_offset);
}

You will also want to edit similar code around line 282 of:
/usr/include/linux/netfilter_ipv6/ip6_tables.h
NOTE:  Recent kernels use struct xt_entry_target for the argument
   for these methods, so use that instead of ipt_entry_target if that
   is the case for your system.

xorp, соответственно, собирается без поддержки netfilter.