karl and paul, expostulating

Wahoo, a nanog issue :slight_smile:

Filtering by connection to the SMTP port, based on source address, very
definitely DOES work.

Filtering packets based on source address makes Ciscos go way slow on
every packet. Filtering based on destination address makes Ciscos go
very fast on most packets and a little slower on SYN-ACKs.

If you enable flow switching it adds little overhead to the box. On a 7505
with 2 sets of full routes and another partial set of routes (and all of
the updates associated), that pushes some pretty significant traffic, I am
filtering approx 25M/sec of data with 25k long extended access list. The
total CPU load on the box is approximately 35%. Oh yeah, the box is also
the DR for area 0 of a fairly large OSPF network (approximately 3k routes).
Before flow switching was enabled we were running at 80% or so (not for
more than a few minutes before we enabled flow switching though).

Sez you. I'd ordinarily expect you to love the idea of "if you don't play
by my rules I will start my own Internet without you on it."

Go ahead and do so, but not with public resources.

And, again, wrong. I want spammers to spend 75 seconds of TCP PCB time on


By blackholing SYN-ACKs and not sending them ICMPs, they lose capacity that
they could otherwise spend spamming other people. I call this "fighting

Is having them time out on DNS requests so that their entire system runs
slower fighting dirty as well?

I operate a cooperative resource. I will not have it used against me.

What kind of a port adapter do you need so as not to have to filter the
traffic to the root name server?

Justin Newton
Network Architect
Erol's Internet Services