Constant low-level attack

Rich Kulawiec rsk at gsp.org
Fri Jun 29 13:30:31 UTC 2012


On Thu, Jun 28, 2012 at 01:31:56PM -0700, Lou Katz wrote:
> 2. Is there anything useful to do with this info other than put the IP addresses into a firewall reject table? 

Do you need to allow inbound ssh connections from the entire planet?

If not, then head over to ipdeny.com and grab the relevant network
allocations for the countries that you *do* need to allow them from.
Block everyone else, allow only the countries you need.

This won't solve your problem completely, but it'll take a substantial
bite out of it, and it'll minimize the number of additional point entries
that you need for annoying hosts whose connections originate in the
set of countries you need to allow.

Then: do you need to allow inbound ssh connections from all operating
systems?

If not, then use passive OS fingerprinting to block those which originate
from operating systems known not to be in use, particularly if those
operatng systems happen to be the ones running on a few hundred million
compromised systems.  (Obviously, this technique is far less effective
is you can't do that.  My condolences.)

And then: consider, instead of point blocks for the remaining annoyances,
use the enclosing /24.  A lot of compromised hosts are not on static
addresses, and guessing that they will bounce around inside (roughly)
a /24 is often a good enough approximation to reality that it works.
Your mileage may vary.

And then: scotch.  Macallan.  18-year.  You've earned it.

---rsk





More information about the NANOG mailing list