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Re: Quarantine your infected users spreading malware
From: David Nolan <vitroth+ () cmu edu>
Date: Tue, 28 Feb 2006 14:39:37 -0500




--On Tuesday, February 28, 2006 14:07:36 -0500 Bill Nash <billn () odyssey billn net> wrote:

The simplest method is to issue a different gateway to a registry of
known offenders, forcing their into a restrictive environment that blocks
all ports, and uses network translation tricks to redirect all web
traffic to a portal.

For cable modems and bridged DSL, you can do this with DHCP, matching
their MAC address. PPPOE/DSL or similiar, you match on user name. Issue
RFC1918 space with a gateway to your quarantine network.

The rest is NAT/PAT and w3proxy stunts. You could pull it off with
something as simple as iptables and squid, after dealing with the DHCP or
authentication servers (ala Radius) to issue to the correct credentials.


We a couple techniques at Carnegie Mellon, depending on the network scenario.

The DHCP based technique outlined above requires no extra infrastructure, just extra configuration, so it is what we use for most of our campus wired networks. We use the same setup as our registration helper network, so our internal name for the DHCP based quarantine system is called QuickReg. An unknown or banned client gets an address in 1918 space and can only access our abuse tracking, patch download and network registration systems.

But on our campus wireless network we use a inline filter system we call AuthBridge, based on ebtables and iptables, to filter & redirect any traffic from unknown/banned clients. This system provides a more seamless user experience, but requires a layer-2 aggregation point where you can pass the traffic through the filter host. Because our wireless is a single campus wide layer-2 network this is more feasible for that network.

Both of these systems are integrated with CMU's DHCP & DNS Management system, NetReg. (not to be confused with Southwestern University's NetReg. Different systems...) The DHCP helper system is a builtin feature, while the AuthBridge system is an add on. (AuthBridge just went through a complete rewrite to use the standard ebtables/iptables in Linux 2.6, and a public release should be available soon...)

For information on NetReg, QuickReg or AuthBridge, see:
http://www.net.cmu.edu/netreg
http://acs-wiki.andrew.cmu.edu/twiki/bin/view/Netreg/WebHome
http://acs-wiki.andrew.cmu.edu/twiki/bin/view/Netreg/NetRegManualDesign#Qui
ckReg
http://acs-wiki.andrew.cmu.edu/twiki/bin/view/Netreg/AuthBridge

(Our abuse tracking system also integrates with NetReg, so going from an external incident report to a machine suspension and email to the user & admins is as simple as dropping an IP and timestamp into a web form...)

-David Nolan
Network Software Designer
Computing Services
Carnegie Mellon University


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