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Re: [RFC] Ndiff
From: "Michael Pattrick" <mpattrick () rhinovirus org>
Date: Mon, 16 Jun 2008 00:37:22 -0400

Hey Thomas,

On Sun, Jun 15, 2008 at 11:14 PM, Thomas Buchanan
<TBuchanan () thecompassgrp net> wrote:
1.  What attribute (or set of attributes) will uniquely determine a
specific host?  For directly connected hosts, it seems like MAC address
is a pretty obvious choice.  For hosts one or more layer 3 hops away, IP
address seems logical, but in certain situations this could lead to a
lot of churn.  One example: a branch office on the Wide Area Network
that you scan on a weekly basis, which consists primarily of DHCP
connected workstations.  They get powered off over the weekend, or their
leases expire, however they get new addresses, this leads to a lot of
false positives for new, changed, or deleted hosts.  In situations like
this, it might be helpful to be able to specify alternate attributes to
track hosts by, for example, reverse DNS name.  If this is possible,
then the tool would need a way to indicate that a host's address has
changed, even though its ports and services may not have.
You've brought up a few good points here, MAC would work well but the
problem is that one scanned host  behind a router/firewall and you
can't maintain the consistency of the format, I think it would be
confusing  to have half the output in macs and half in IPs. A possible
feature would be to let the user select how they wanted to sort the
output; mac, ip, or dns. DNS may also pose a problem for networks
where the domain is dynamic and based on the ip
(10.9.8.7.workstations.company.com).

Also, I don't think that it will give all that many false positives,
most corporate workstations run the same images with the same firewall
policies, services, etc on all workstations. But I can see how this
could become annoying if you ran a mixed environment so half the hosts
changed from Windows services to Mac services.

2.  In your example for host 10.9.8.7, how does the XML indicate the
previous state of a new port?  In the text output, it indicates port 53
went from filtered to open, which is nice to know, but I don't see this
information in the corresponding XML.
Yes, I should have explained that better, in the xml 'add' and 'del'
are associated with a transition too and from a host state that isn't
listed in the logs. Not scanned, Filtered, and Closed when there are
too many Closed ports. I did this for the reason that you pointed out,
based on some logs its not possible to know the exact state of a host,
so I just leave it blank. If it went from being listed as closed to
listed as open in the log I would use 'chgport' and 'chgstate'.

Cheers,
Michael

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