[TriLUG] IPv4 routing I don't understand...

[Mauricio Tavares via TriLUG]

On Fri, May 8, 2015 at 10:06 AM, Brian Henning via TriLUG
<trilug at trilug.org> wrote:
> Hi Folks,
>
> I was hoping someone could help me understand a weird behavior I'm seeing when my home network routes to the outside world.  Here's the scenario:
>
>  [gateway router    ]
> [eth1:192.168.0.80/24]
> [eth0:71.70.212.129/22]
>      |
>  [ bridge modem ]
>      |
>  { the great beyond }
>
> The external interface is cabled to the modem which is [supposed to be, presumed to be] in bridging mode.
>
> Here is the gateway's routing table:
> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
> 192.168.0.0     0.0.0.0         255.255.255.0   U     0      0        0 eth1
> 10.32.4.0       0.0.0.0         255.255.255.0   U     0      0        0 eth1
> 10.1.1.0        0.0.0.0         255.255.255.0   U     0      0        0 vmnet8
> 71.70.208.0     0.0.0.0         255.255.240.0   U     0      0        0 eth0
> 169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth1
> 0.0.0.0         71.70.208.1     0.0.0.0         UG    0      0        0 eth0
>
> Here is a traceroute to a well-known DNS server (with timing omitted for space):
> traceroute to 8.8.4.4 (8.8.4.4), 30 hops max, 40 byte packets
>  1 192.168.0.1
>  2 71.70.208.1
>  3 66.26.47.197
>  4  24.25.62.178
>  5  24.93.64.186
>  6  107.14.19.48
>  7  107.14.19.11
>  8  216.156.108.97
>  9  216.156.108.114
> 10  209.85.240.243
> 11  64.233.175.225
> 12  8.8.4.4
>
> Why is 192.168.0.1 in there?  There is no device at 192.168.0.1 on my network, and no reason for it to hop there first seems evident in the routing table.
>
      Are you sure it is not your cable modem IP? I know the surfboard
modem is 192.168.100.1

> I've known TWC modems to "forget" they're bridged; could that be the cause?  eth0 is addressed via DHCP, and refreshing its lease gives it the same publicly-routable address.
>
> Thanks,
> -B
>
>
>
> --
> This message was sent to: raubvogel at gmail.com <raubvogel at gmail.com>
> To unsubscribe, send a blank message to trilug-leave at trilug.org from that address.
> TriLUG mailing list : http://www.trilug.org/mailman/listinfo/trilug
> Unsubscribe or edit options on the web  : http://www.trilug.org/mailman/options/trilug/raubvogel%40gmail.com
> Welcome to TriLUG: http://trilug.org/welcome