Hi Cary, On Mon, 13 Jun 2011, Cary Wiedemann wrote:
Greetings list,
We have a few customers in the Fairfax County/Washington DC area with XO-provided T1 circuits that can only access hosts with an EVEN numbered last octet in their IP address.
For example I personally host a server in Equinix Ashburn (with Carpathia) on a /28 and the XO T1's can only ping the EVEN numbered IPs, for example: 209.222.152.120 - can ping/http/etc 209.222.152.121 - no access 209.222.152.122 - can ping/http/etc 209.222.152.123 - no access
The is doubly-confirmed via traceroute as only even numbered routers' responses make it back.
XO recently implemented automatic abuse-related filtering at their edge routers. You may want to check to make sure these individual IPs aren't triggering one of the automatic filtering rules that null routes the /32s. Hope this helps, -- William R. Lorenz