In trying to diagnose a failover problem with my Cisco ASA 5520 firewalls, I ran a traceroute to www.btfl.com and, much to my surprise, some of the hops came back as RFC 1918 addresses.
Just to be clear, this host is not behind my firewall and there is no VPN involved. I have to connect across the open internet to get there.
How/why is this possible?
asa# traceroute www.btfl.com
Tracing the route to 157.56.176.94
1 <redacted>
2 <redacted>
3 <redacted>
4 <redacted>
5 nap-edge-04.inet.qwest.net (67.14.29.170) 0 msec 10 msec 10 msec
6 65.122.166.30 0 msec 0 msec 10 msec
7 207.46.34.23 10 msec 0 msec 10 msec
8 * * *
9 207.46.37.235 30 msec 30 msec 50 msec
10 10.22.112.221 30 msec
10.22.112.219 30 msec
10.22.112.223 30 msec
11 10.175.9.193 30 msec 30 msec
10.175.9.67 30 msec
12 100.94.68.79 40 msec
100.94.70.79 30 msec
100.94.71.73 30 msec
13 100.94.80.39 30 msec
100.94.80.205 40 msec
100.94.80.137 40 msec
14 10.215.80.2 30 msec
10.215.68.16 30 msec
10.175.244.2 30 msec
15 * * *
16 * * *
17 * * *
and it does the same thing from my FiOS connection at home:
C:\>tracert www.btfl.com
Tracing route to www.btfl.com [157.56.176.94]
over a maximum of 30 hops:
1 1 ms <1 ms <1 ms myrouter.home [192.168.1.1]
2 8 ms 7 ms 8 ms <redacted>
3 10 ms 13 ms 11 ms <redacted>
4 12 ms 10 ms 10 ms ae2-0.TPA01-BB-RTR2.verizon-gni.net [130.81.199.82]
5 16 ms 16 ms 15 ms 0.ae4.XL2.MIA19.ALTER.NET [152.63.8.117]
6 14 ms 16 ms 16 ms 0.xe-11-0-0.GW1.MIA19.ALTER.NET [152.63.85.94]
7 19 ms 16 ms 16 ms microsoft-gw.customer.alter.net [63.65.188.170]
8 27 ms 33 ms * ge-5-3-0-0.ash-64cb-1a.ntwk.msn.net [207.46.46.177]
9 * * * Request timed out.
10 44 ms 43 ms 43 ms 207.46.37.235
11 42 ms 41 ms 40 ms 10.22.112.225
12 42 ms 43 ms 43 ms 10.175.9.1
13 42 ms 41 ms 42 ms 100.94.68.79
14 40 ms 40 ms 41 ms 100.94.80.193
15 * * * Request timed out.
