NMAP Host Scan picks up private IP's on another network

[Charlie Aquilino <Charlie.Aquilino () avianllc com>]

Hello,

I'm running a host scan via Zenmap and it is picking up 10.x.x.x IP addresses on other private networks. Here's a 
traceroute for one of those IPs:
"C:\Users\admin-charlie>tracert 10.113.63.192

Tracing route to 10.113.63.192 over a maximum of 30 hops

  1     1 ms     1 ms     1 ms  10.1.1.1
  2    10 ms    15 ms    10 ms  10.210.192.1
  3    18 ms    11 ms    23 ms  static-216-36-30-138.cpe.metrocast.net [216.36.30.138]
  4    38 ms    34 ms    41 ms  static-216-36-30-238.cpe.metrocast.net [216.36.30.238]
  5    30 ms    27 ms    26 ms  static-206-53-95-141.cpe.metrocast.net [206.53.95.141]
  6    43 ms    35 ms    33 ms  10.113.63.192

Trace complete."

10.113.63.192 is not on our network. You can see that NMAP seems to leave our network, go through some public IP's of 
our ISP (MetroCast), and then discovers machines behind the ISP's public IP address. Why is this happening? Is there 
anything I should be concerned about since our firewall blocks everything not from a certain few IP addresses?

Thank you in advance for your help,
Charlie Aquilino
IT Manager
AVIAN LLC

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