RE: Re: Vlan's as effective security measures?

[<hugh_fraser () dofasco ca>]

Regardless of the VLAN technology chosen, the basic reason for investing
in this kind of technology is to manage bandwidth and isolate traffic,
not provide security. As such, the vendors haven't invested a lot in
security. But beyond that, there are basic authentication issues that
make it difficult to implement a strong security solution based upon
VLANs. 

Policies controlling access to VLANs depend upon some method of
identifying the client, and it's usually either a MAC address or a
switch port. MAC addresses are readily obtained and almost as easily
forged as IP addresses, allowing access to a MAC-based VLAN. Port-based
identification relies on restricted access to the ports themselves, or
to the drop connected to the port.

In both cases, bypassing the VLAN security isn't something that happens
by accident, but if you're concerned about security you're planning for
malicious activity. Newer technologies can do stronger authentication at
the port, but aren't widely used. And it's possible to configure most
networking infrastructure to alert you to unexpected changes if they
occur, but this information is rarely incorporated into a security
auditting system, and generally go un-noticed except by the network
group when they're debugging problems.

It requires extra diligence to ensure that VLANs provide anywhere near
the security most people expect. In my experience, this extra diligence
doesn't happen, and VLANs are incorrectly understood to provide secure
channels.

> -----Original Message-----
> From: Brian Ford [mailto:brford () cisco com] 
> Sent: Thursday, February 12, 2004 1:14 PM
> To: firewall-wizards () honor icsalabs com
> Cc: jhall () ptavvs net; Ware, Larry
> Subject: Re: Re: [fw-wiz] Vlan's as effective security measures?
>
>
> John,
>
> And cars crash and cars burn and people are dying in cars all the 
> time.   And cars can be made to carry disease and explosives 
> and kill many 
> people with just one car and driver! So let's all abandon our 
> cars and 
> start walking to work every morning.  If we're late the boss will 
> understand because cars are dangerous.  ;-)
>
> You should probably research the switch that you buy and use 
> in order to 
> make sure that it doesn't do these things.
>
> Your mileage may vary!
>
> Liberty for All,
>
> Brian
>
> At 12:00 PM 2/10/2004 -0500, 
> firewall-wizards-request () honor icsalabs com wrote:
> > Message: 4
> > Date: Mon, 09 Feb 2004 12:52:31 -0800
> > From: John Hall <jhall () ptavvs net>
> > To: "Ware, Larry" <LWare () e-one com>
> > Cc: "'firewall-wizards () honor icsalabs com'"
> > <firewall-wizards () honor icsalabs com>
> > Subject: Re: [fw-wiz] Vlan's as effective security measures?
> >
> >
> > 1.  A surprising number of network devices' VLAN implementations
> >     will leak packets between VLANs under heavy loads, or in some
> >     cases randomly all the time.
> > 2,  Some switches have a single forwarding database which includes
> >     VLAN tags and a host presenting a carefully chosen MAC address
> >     can sometimes hijack traffic for a host on another 
> VLAN. 3.  Some 
> > switches flood ARP requests across VLANs. 4.  Some switches 
> flood all 
> > traffic under heavy load. 5.  Few switches and routers have adequate 
> > configuration security.
> >
> > Don't depend on VLANs to guarantee the separation of two 
> networks that 
> > *must* be separated.  Your security is only as good as the weakest 
> > element in your infrastructure and the security of most 
> switches (and 
> > to a lesser extent routers) is pretty weak.
> >
> > JMH
> >
> > Ware, Larry wrote:
> >
> > > Forgive a long out of field, and now working on getting back up to 
> > > speed firewall admin, but would someone care to educate me 
> concerning 
> > > the security issues related to VLAN's? I have lots of 
> them, and need 
> > > to know why a VLAN is not an effective adjunct to firewall 
> and router 
> > > security policies. -larry
>
>
> Brian Ford
> Consulting Engineer, Security & Integrity Specialist
> Office of Strategic Technology Planning
> Cisco Systems Inc.
> http://www.cisco.com/go/safe/
>
> The opinions expressed in this message are those of the 
> author and not 
> necessarily those of Cisco Systems, Inc..
>
> This email address is transmitted from San Jose, California, U.S.A..
>
>
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