Internal IPs routing through external DNS

[360fish]

Is there a common reason why internal IPs would route outside the network, then back in?

Network - DSL router, static IP, bridge mode. Internal vpn router in gateway mode, running NAT/DHCP, VPN tunnels (router to router and PPTP). Internal PCs are all on the same workgroup, no wins/dns. All running Windows XP or XP embedded.

For example, ip is 10.10.10.x subnet 255.255.255.0. Address assigned by DHCP, tracert another computer on the same 10.10.10.x network by NAME OR IP.

gateway->external DNS server->gateway->target

Other identically-configured sites do not exhibit this behavior

 

[Noway2]

Generally speaking, RFC-1918 addresses, such as 10.0.0.0/8 should not appear on an external or public network segment. A common problem with DNS servers is to leak these addresses in queries and it usually means something is not configured properly. Typically there are zone files to catch these types of addresses.

This is similar to the concept of using a bogon filter, which is also a good security measure.