Routers have multiple addresses, typically at least 3 if not more: one facing end users, one facing upstream and a loop back address. Some network operators choose to use a loop back address for traffic replies in things such as traceroutes.
Especially as some may be using rfc1918 addresses on some interfaces.

-------- Original message --------From: Jon Schewe <jpschewe at> Date: 9/3/17  7:47 AM  (GMT-06:00) To: TCLUG Mailing List <tclug-list at> Subject: [tclug-list] Odd networking on Comcast 
I'm trying to debug some issues with my internet connection. I have Comcast and the traceroute results are not coming back what I expect. On my router my routing table looks like this:
>netstat -rnKernel IP routing tableDestination     Gateway         Genmask         Flags   MSS Window  irtt Iface0.0.0.0         UG        0 0          0 enp1s1073.37.164.0   U         0 0          0 enp1s10
Given that, I expect the first hop in a traceroute to be, but it's not.>traceroute -n to (, 30 hops max, 60 byte packets 1  8.890 ms  14.915 ms  15.659 ms 2  14.833 ms  15.604 ms  15.575 ms 3  14.502 ms  14.484 ms  14.665 ms 4  15.455 ms  16.596 ms  16.574 ms 5  28.011 ms  26.859 ms  26.841 ms 6  24.289 ms  19.757 ms  22.386 ms...
Can anyone explain what's going on here?
- Jon

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