On Mon, Jun 13, 2011 at 11:08 AM, Cary Wiedemann <carywiedemann@gmail.com> 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.
This speaks very strongly of a link-aggregation scheme with an undetected link failure. Many implementations can hash based on the destination IP address to load balance traffic across multiple links. Some NSPs don't properly implement a link aggregation negotiation protocol like LACP or PAGP and just leave things in an enabled state. This leads to failures like this. Level3 seems to have an outage like this every 6 - 9 months, I've found.