Bogons

http://www.kuro5hin.org/story/2006/7/3/211811/5310

What are bogon IPs you are asking? Well I didn’t know either. There is no reason to really. Here is what they are.

Officially they are not IP blocks officially allocated by IANA or RIRs. Additionally, they should not be routable. This is no big deal unless you are an organization that puts these lists in your routers so that if they show up on your WAN circuit the bad packets are immediately dropped. Still, this is a common practice with some organization, no big deal nothing wrong with that. However, there is a very big problem that happens very rarely and it happened to us.

The /20 CIDR block that had been allocated to us by our tier 1 backbone provider was allocating an IANA unallocated /16 CIDR block! The result was 1000s of ISPs dropping our packets to them. This was happening on DNS lookups, MX lookups and for websites. For example we were getting calls from our customers saying that they could not get to a airline’s website or some email was not getting to recipients.