Creating and Maintaining Home Networks
Testing Your Router From The Outside


ShieldsUP!! -- Internet Connection Security for Windows Users
by Steve Gibson, Gibson Research Corporation

  Your use of the Internet security vulnerability profiling
  services on this site constitutes your FORMAL PERMISSION for
  us to conduct these tests and requests our transmission of
  Internet packets to your computer. ShieldsUP!! benignly
  probes the target computer at your location. Since these
  probings must travel from our server to your computer, you
  should be certain to have administrative right-of-way to
  conduct probative protocol tests through any and all
  equipment located between your computer and the Internet.
DNS Nameserver Spoofability Test
Understanding ICMP and why you shouldn't just block it outright

You need your External IPv4 address for Nmap Online (below)

Test Firewall

Test Your Router