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I'd like to get some insight as to how I can possibly access network devices that are on a different IP range (obviously not mine) compared to what is configured on my wifi router?

setup

  • home wifi connection on private network (192.168.1.x)
  • wireless router
  • setup to be on 192.168.1.1 / 255.255.255.0
  • DHCP enabled only
  • connected to our own secured wifi network
  • all our devices and computers are on the 192.168.1.x network
  • router logs dont show any 192.168.2.x IPs (DHCP leases & wifi logs only show our devices IPs)

$ traceroute 192.168.2.69

traceroute to 192.168.2.69 (192.168.2.69), 30 hops max, 60 byte packets
1 RT-G32 (192.168.1.1)  1.240 ms  1.375 ms  1.589 ms
2 10.17.64.1 (10.17.64.1)  10.396 ms  10.400 ms  10.372 ms
3 192.168.100.13 (192.168.100.13)  14.912 ms  16.572 ms  16.487 ms
4 192.168.2.69 (192.168.2.69)  13.146 ms  13.127 ms  14.658 ms

$ traceroute  192.168.2.90

traceroute to 192.168.2.90 (192.168.2.90), 30 hops max, 60 byte packets
1  RT-G32 (192.168.1.1)  1.466 ms  1.418 ms  1.551 ms
2  10.17.64.1 (10.17.64.1)  11.025 ms  11.005 ms  10.975 ms
3  192.168.100.13 (192.168.100.13)  10.958 ms  15.729 ms  15.715 ms
4  192.168.2.90 (192.168.2.90)  15.640 ms  15.561 ms  15.532 ms

I'm puzzled as to where the 10.17.64.1 comes from.. it seems to be a gateway of some sort, but how come I can access it from my network?!

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Add a traceroute to an internet site eg. unix.stackexchange.com to see which part of the route is more or less identical. –  jippie Jul 11 '12 at 10:38
    
@jippie thanks to your comment, these are effectively part of the ISP network and subnetworks. –  fduff Jul 11 '12 at 18:34
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2 Answers

Your router does not know the entire internet, but it knows another machine that might. The machine we expect/hope to know the internet is called the "default gateway". Packets are forwarded to the default gateway if a router doesn't know any better. Most routers "know" such a default gateway.

So, if your router receives a packet addressed to a host in a subnet it doesn't know (192.168.2.X) it forwards that packet to the default gateway. In your case that's another router with the IP-address 10.17.64.1. And that router follows the same train of thought: either it knows a subnet and the next router in the direction of that subnet, or it will forward the packet to its default gateway. Rinse, repeat until the packet can be sent to the actual destination.

Every router along the way is listed in your traceroute output, theoretically.

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If you will traceroute to 192.168.2.69, your packets will be routed to your network's gateway (192.168.1.1) and then further on via that machine's default route. 10.17.64.1 is a machine from your ISP probably, or a cable modem or whatever other device.

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