New subject: Odd issue when re-numbering - new IP only routable from some IPs.

7 Nov 2011

Hi all,

I've come across a strange issue partway through renumbering, where a new
IP is only responding from some hosts on the Internet, and seems only able
to route to some IPs itself.

The current config (mid-way through the change) is:

ip -4 addr show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state
UP qlen 1000
    inet 212.13.194.116/23 brd 212.13.195.255 scope global eth0
    inet 85.119.82.116/21 scope global eth0

ip -4 route show
212.13.194.0/23 dev eth0  proto kernel  scope link  src 212.13.194.116
85.119.80.0/21 dev eth0  proto kernel  scope link  src 85.119.82.116
default via 85.119.80.1 dev eth0  metric 100

My new IP 85.119.82.116 is pingable from some devices, but not others (the
old IP is responding from all).

And outgoing traffic is also affected, for example I can't connect to
Google's Public DNS server 8.8.8.8:

traceroute -n 8.8.8.8
traceroute to 8.8.8.8 (8.8.8.8), 30 hops max, 60 byte packets
 1  85.119.80.17  0.180 ms  0.213 ms  0.193 ms
 2  212.13.194.4  0.466 ms  0.593 ms  0.613 ms
 3  194.153.169.233  2.631 ms  2.545 ms  2.526 ms
 4  134.222.231.29  15.405 ms  15.388 ms  15.366 ms
 5  * * *
 6  * * *
 7  * * *

There's lots of other IPs I can and can't connect to (for example
158.43.240.4 works fine), I've not spotted a pattern yet.

Incoming traceroute's look odd too:

traceroute -n 85.119.82.116
traceroute to 85.119.82.116 (85.119.82.116), 30 hops max, 60 byte packets
 1  212.64.153.2  0.581 ms  0.595 ms  0.622 ms
 2  92.52.77.60  136.363 ms  136.371 ms  136.409 ms
 3  92.52.76.198  0.178 ms  0.196 ms  0.193 ms
 4  77.67.75.181  0.271 ms  0.289 ms  0.264 ms
 5  89.149.185.165  1.324 ms 89.149.183.178  1.317 ms 89.149.185.230  1.295
ms
 6  195.66.224.138  2.021 ms  1.965 ms  2.032 ms
 7  129.250.5.25  2.226 ms  2.227 ms  1.944 ms
 8  194.153.169.242  2.068 ms 194.153.169.241  2.133 ms 194.153.169.242
2.097 ms
 9  85.119.80.16  1.988 ms  1.996 ms 85.119.80.17  2.117 ms

If you look at step 9, that's 2 different hosts responding to the same
traceroute. Is it possible someone else has setup a host using my new IP at
some point, and messed up the routing, then switched their hosts IP?

I've obviously done something silly, but I must be going blind.

Any ideas?
Ewan