Re: ISMS working group and charter problems

In message <E8014931-944D-42C9-A950-F3B1CFB1B0C5@muada.com>, Iljitsch van Beijn
um writes:
>On 7-sep-2005, at 1:04, Steven M. Bellovin wrote:
>
>>> Either the firewall
>>> successfully blocks the protocol and the firewall works and the
>>> protocol doesn't, or the firewall doesn't manage to block the
>>> protocol and the protocol works but the firewall doesn't. So whatever
>>> happens, someone is going to be unhappy.
>
>> Not at all.  Often, a firewall needs to know a fair amount about the
>> protocol to do its job.  FTP is the simplest case -- it has to look  
>> for
>> the PORT (and, in some configuration, the PASV) command.  H.323 and  
>> SIP
>> are more complex.
>
>I'm not very comfortable with the notion of having a third party  
>device deciding what is valid communication between two hosts  
>connected to the internet. This is just too fragile. For instance, a  
>popular filter on *BSD (they're all named [i]pf[w] so I can never  
>remember which is which) is unable to handle RFC 1323 window scaling  
>properly. PIX firewalls truncate(d) EDNS0 packets. ICMP packet too  
>bigs are filtered in many places, as is ECN.
>
>I recognize that carrying all existing firewalls to the scrap heop  
>won't immediately solve our problems, but we do have to realize that  
>current filter practice do almost as much harm as they do good. We  
>really need better stuff here.
>
>(It's amusing to see that to some people, security means encrypting  
>their communication, while to others it means inspecting that same  
>communication.)
>
I opt for each in its place.  I'm also an advocate for distributed 
firewalls.  But I *really* don't want to refight the whole firewall 
issue yet again; I've been through that too many times in the last 
decade or so.

For right now, though, the issue is engineering.  Again, the vast 
majority of hosts are behind firewalls.  Is the philosophical issue 
that important that we should ignore it?  I don't think so.

		--Steven M. Bellovin, http://www.cs.columbia.edu/~smb

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