RE: UUNet Offer New Protection Against DDoS

I struggled with this, and came up with the following.

We basically use a standard route-map for all customers where the first
term looks for the community. The customer also has a prefix-list on
their neighbor statement allowing their blocks le /32. The following
terms (term 2 and above) in the route-map which do NOT look for the
customer discard community, have a different standard/generic
prefix-list evaluation which blocks cruft and permits ge 8 le

By doing this, I only accept a customer /32 from his dedicated
prefix-list when it has the DOS discard community, otherwise I catch
them with the ge 8 le 24 in the following terms.

Jason Lumenello
IP Engineering
XO Communications

From: [] On Behalf


Stephen J. Wilcox
Sent: Wednesday, March 03, 2004 3:48 PM
To: james
Subject: Re: UUNet Offer New Protection Against DDoS

I'm puzzled by one aspect on the implementation.. how to build your
prefix filters.. that is, we have prefix-lists for prefix and length.
at present we can only accept a tagged route for a whole block.. not


if the
announcement is a /16 etc !

Now, I could do as per the website at which means we have a
entry to match the community before the filtering .. but that would


A lot of people seem to be doing this.

Mind if I ask what's the harm of letting customers announce /32 or /29s into your core as long as you filter at your borders?

The additional prefixes are not going to kill your routers, and it allows the customer more finely tuned traffic controls. IOW: Seems there is some utility and no harm.

there is nothing (well very little) new in the world:


Does anyone know if Cogent offer such a community?
Anyone from Cogent on the line?