Fwd: RE: [EXT] Fwd: Re: problems sending to prodigy.net hosted email

[list at satchell.net (Stephen Satchell)]

Linux systems have the ability, given enough RAM, to associate almost 
any number of IP addresses to a given interface.  Our IP allocation 
database kept track of who was using what IP address.  I wrote some 
queries to collect all unassigned IP addresses, and to construct the 
appropriate shell commands to assign those IP addresses to Ackbar's 
interface.  Part of the program would also remove any allocated IP 
addresses from the server automtically.

Worked like a charm.

Whenever someone would nmap our address space, there would be at most 
one ARP request for the address; the router would then remember the 
IP->MAC association for the subsequent scans for a period of time -- 30 
minutes if we were renumbering, 12 hours otherwise.

The Ackbar server lived attached to our main distribution switch, so 
that subsequent traffic to those unused IP addresses stayed out of the 
server farm.  We had some, er, "interesting" denial of service attacks 
that didn't do as much damage as they could have.


-------- Forwarded Message --------
Subject: RE: [EXT] Fwd: Re: problems sending to prodigy.net hosted email
Date: Tue, 20 Mar 2018 17:15:25 +0000
From: Charles Bronson <cbronson at iec-electronics.com>
To: nanog at nanog.org <nanog at nanog.org>

If this isn't pertinent to the list, feel free to answer privately. How 
did you implement the server that got rid of ARP storms?


Charles Bronson



-----Original Message-----
From: NANOG [mailto:nanog-bounces at nanog.org] On Behalf Of Stephen Satchell
Sent: Monday, March 19, 2018 9:31 PM
To: nanog at nanog.org
Subject: [EXT] Fwd: Re: problems sending to prodigy.net hosted email

Two DNS servers hosted on one box (or VM object), even with two 
addresses, is easily compromised by DDoS amplification attacks.  That's 
the norm for a number of "web control panel" systems like Plesk and CPanel.

It depends on the scale of your operations.  Last time I was in that 
situation, I had roughly 25,000 domains spread across 30 servers.  Life 
became MUCH simpler when I put up dedicated, and high-power, physical 
systems running non-recursive BIND for DNS1 and DNS2, as well as another 
pair of boxes running recursive servers as DNS3 and DNS4.

Getting QMail and Exim to "smart host" to my monster MX servers proved 
to be pretty easy, and I even was able to get the web servers to tell me 
when a mailbox was full so I could reject the SMTP exchange at the edge, 
instead of generating backscatter.

And, with a pool of roughly 4,000 IP addresses, I got rid of ARP storms 
in our network by putting up a little server called "ackbar", that was 
configured to respond to all otherwise unused IP address in our pool. 
(Edge routers were Cisco 7000 class, with DS3 uplinks.)

Lessons learned well.

-------- Forwarded Message --------
Subject: Re: problems sending to prodigy.net hosted email
Date: Mon, 19 Mar 2018 17:55:33 +0100
From: Chris <chris2014 at postbox.xyz>
To: C. Jon Larsen <jlarsen at richweb.com>
CC: nanog at nanog.org

On Mon, 19 Mar 2018 11:56:16 -0400 (EDT) C. Jon Larsen wrote:

> > Why not? Never had a problem with multiple services on linux, in 
> > contrast to windows where every service requires its own box (or at 
> > least vm).
> 
> Go for it ! Failure is an awesome teacher :)

Don't really see a problem, especially since you normally always have 
two DNS servers...

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